Living and radiological anatomy of the head and neck for dental students 9781910451151, 1910451150

Citation preview

Living and Radiological Anatomy of the Head and Neck for Dental Students

For the full range of M&K Publishing books please visit our website: www.mkupdate.co.uk

Living and Radiological Anatomy of the Head and Neck for Dental Students P. F. Harris, M. Al-Ismaily and R. Arora

Living and Radiological Anatomy of the Head and Neck for Dental Students P.F. Harris, M. Al-Ismaily and R. Arora ISBN: 9781910451-15-1 First published 2017 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior permission of the publishers or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency, 90 Tottenham Court Road, London, W1T 4LP. Permissions may be sought directly from M&K Publishing, phone: 01768 773030, fax: 01768 781099 or email: [email protected] Any person who does any unauthorised act in relation to this publication may be liable to criminal prosecution and civil claims for damages.

British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Notice Clinical practice and medical knowledge constantly evolve. Standard safety precautions must be followed, but, as knowledge is broadened by research, changes in practice, treatment and drug therapy may become necessary or appropriate. Readers must check the most current product information provided by the manufacturer of each drug to be administered and verify the dosages and correct administration, as well as contraindications. It is the responsibility of the practitioner, utilising the experience and knowledge of the patient, to determine dosages and the best treatment for each individual patient. Any brands mentioned in this book are as examples only and are not endorsed by the publisher. Neither the publisher nor the authors assume any liability for any injury and/or damage to persons or property arising from this publication.

To contact M&K Publishing write to: M&K Update Ltd · The Old Bakery · St. John’s Street Keswick · Cumbria CA12 5AS Tel: 01768 773030 · Fax: 01768 781099 [email protected] www.mkupdate.co.uk Designed and typeset by Mary Blood Printed by H&H Reeds, Penrith.

Contents List of figures vi About the authors ix Foreword xi Acknowledgements xii Introduction xiii 1 Practical tips on head and neck examination 1 2 Bony landmarks 3 3 Testing the cranial nerves 9 4 Examining the buccal cavity and oropharynx 19 5 Examining the arterial pulses, salivary glands and lymph nodes 25 6 The temporomandibular joint (TMJ) and the muscles of mastication 31 7 Neck landmarks 37 8 Joints and movements of the head and neck 41 9 The scalp, ear and eye 45 Further reading 49 Index 50

List of figures

Figure 2.1 Frontal x-ray of head showing air sinuses 3 Figure 2.2 Frontal 3-dimensional CT reconstruction scan of skull 3 Figure 2.3 Palpating the supraorbital foramen 4 Figure 2.4 Palpating the infraorbital foramen 4 Figure 2.5 Posterior 3D CT reconstruction of skull 5 Figure 2.6 Lateral 3D CT reconstruction of skull 5 Figure 2.7 Palpating the external occipital protuberance 6 Figure 2.8 Palpating the mastoid process 6 Figure 2.9 Palpating the zygomatic arch 7 Figure 2.10 Palpating the malar eminence 7 Figure 2.11 Palpating the base of the mandible 7 Figure 2.12 Palpating the angle of the mandible 7 Figure 3.1 Testing the olfactory nerve 9 Figure 3.2 Testing pupil light reflex 10 Figure 3.3 Ophthalmoscopy of retina 11 Figure 3.4 Testing extrinsic eye muscles 12 Figure 3.5 Horizontal CT scan of head at level of orbits 12 Figure 3.6 Testing the sensory facial distribution of the trigeminal nerve: Testing the ophthalmic division 13 Figure 3.7 Testing the sensory facial distribution of the trigeminal nerve: Testing the maxillary division 13 Figure 3.8 Testing the sensory facial distribution of the trigeminal nerve: Testing the mandibular division 14 Figure 3.9 Testing the lingual branch of the trigeminal nerve 14 Figure 3.10 Testing the palpebral part of orbicularis oculi 15 Figure 3.11 Testing the dilators of buccal orifice 15 Figure 3.12 Testing the buccinator 15 Figure 3.13 Testing the left sternomastoid muscle; turning the head to the opposite side is resisted 17 Figure 3.14 Testing the intrinsic muscles of the tongue 17 Figure 3.15 Testing the extrinsic muscles of the tongue 17 Figure 3.16 Sagittal CT scan of mouth 18

vi

Figure 4.1 Examining the buccal vestibule 19 Figure 4.2 Dental planogram 19 Figure 4.3 Sagittal CT scan of head 20 Figure 4.4 The pterygomandibular raphe 20 Figure 4.5 Close-up of the pterygomandibular raphe 20 Figure 4.6 Sagittal CT scan of mouth 21 Figure 4.7 Dorsum of tongue 21 Figure 4.8 Close-up of pink tastebuds on dorsum of the tongue 22 Figure 4.9 Ventrum (undersurface) of tongue 23 Figure 4.10 Oropharynx 23 Figure 4.11 Lymphoid tissue on dorsum of oropharynx 24 Figure 4.12 Sagittal CT scan of head 24 Figure 5.1 Carotid angiogram 25 Figure 5.2 A 3D reconstruction of a CT scan of carotid arteries and branches 26 Figure 5.3 Palpating the carotid pulse 26 Figure 5.4 Palpating the superficial temporal pulse 26 Figure 5.5 Palpating the facial pulse 26 Figure 5.6 Transverse CT scan of the head at the level of the parotid gland 27 Figure 5.7 Palpation of parotid duct 28 Figure 5.8 Orifice of parotid duct in upper vestibule 28 Figure 5.9a Submandibular gland (lateral view) 29 Figure 5.9b Parotid gland (frontal view) 29 Figure 5.10a Palpating the superficial ring of lymph nodes: Palpating the submental nodes 30 Figure 5.10b Palpating the submandibular nodes 30 Figure 6.1 A 3D CT bony reconstruction of the TMJ (mouth closed) 31 Figure 6.2 Coronal CT scan of the head at the level of the TMJ 32 Figure 6.3 A 3D CT bony reconstruction of the TMJ (mouth open) 32 Figure 6.4 Examining the TMJ movement 33 Figure 6.5 Horizontal CT scan of head at level of TMJ 34 Figure 6.6 A 3D CT bony reconstruction of mandible 34 Figure 6.7 Coronal CT scan through the head at the level of the TMJ 35 Figure 6.8 Testing elevators of mandible 35 Figure 6.9 Coronal CT scan through the head at the level of the zygomatic arch 35 Figures 6.10, 6.11 Testing depressors of mandible 36 Figure 6.12 Testing pterygoid muscles 36

vii

Figure 7.1 Palpating hyoid bone 37 Figure 7.2 Palpating thyroid cartilage 37 Figure 7.3 Palpating cricoid cartilage 38 Figure 7.4 Auscultation of trachea 38 Figure 7.5 Transverse CT scan of neck at level C5 39 Figure 8.1 A CT 3D reconstruction scan of skull and cervical spine 4.1 Figure 8.2 Transverse CT scan of neck level of C1 vertebra 42 Figure 8.3 Resisting head flexion 42 Figure 8.4 Active full head flexion 43 Figure 8.5 Active head extension 43 Figure 8.6 Active lateral head rotation 43 Figure 9.1 Testing layer 4 of the scalp 45 Figure 9.2 The auricle 46 Figure 9.3 Tympanic membrane 46 Figure 9.4 Eyelid and conjunctival fornix 47

viii

About the authors Professor P.F. Harris is Emeritus Professor of Anatomy at the University of Manchester Medical School (UK). He has extensive experience in teaching undergraduate and postgraduate medical and dental students and is particularly interested in clinically applied anatomy. His expertise includes teaching how to examine accessible structures in the living body, particularly those of clinical significance, and the use of different forms of radiological imaging to correlate with living anatomy. Dr R. Arora is Dean of Oman Dental College. He has a particular interest in dental education and specialises in Endodontics. Dr M. Al-Ismaily is past Head of Dental Services and Oro-maxillary and Facial Surgery, Ministry of Health, Sultanate of Oman.

ix

Foreword This book is intended to show how practical anatomy teaching for pre-clinical students can be used to bridge the gap between ‘textbook’ topographical anatomy and the anatomy of the living subject, as experienced in clinical practice. Comprehensive descriptions are given of techniques to examine accessible, clinically significant anatomical structures in the living body; and these structures are correlated with relevant radiological imaging. The structure of the book is ideally suited to small group activity. P.F. Harris, M. Al-Ismaily and R. Arora Manchester, Muscat, 2017

xi

Acknowledgements We wish to thank Rashad Al-Wahaibi and Natasha Russell for their photographic skill, Dr Noor Al-Saadi and Dr Amir Awwad for providing radiographic material, and Khalfan Al-Rawahi and John Britton for volunteering as models. Professsor S. Vernon kindly supplied the fundus photograph.

xii

Introduction A sound knowledge of the regional anatomy of the head and neck is essential for the safe and effective practice of clinical dentistry. In some dental schools, cadaver dissection and/or the use of virtual three-dimensional (3D) models of dissections is a major component of the pre-clinical curriculum. In other dental schools, for a variety of reasons, dissection is not practised. Whatever the case on their particular course, it is important for students to realise that much clinically relevant and important anatomy can be learned by examining the living subject in conjunction with radiological images, especially those using CT reconstruction of living subjects. Moreover, this integrated approach (utilising relevant radiological information in support of clinical examination) sharpens two key skills needed for clinical work: careful inspection and palpation (which requires manual dexterity). In addition, radiological images enable students to explore functional aspects of anatomical structures that are not visible in the cadaver. This practical guide gives detailed instructions on how to locate and examine anatomical structures. It encourages students to work together in small groups, examining each other and themselves as living models. It is anticipated that the content could form the basis of practical teaching sessions in anatomy. As they progress through the book, students will become more confident about correlating living and radiological examination. The radiographic content utilises the latest forms of imaging and is intended to complement, where relevant, the topographical features in the living subject.

xiii

–1–

Practical tips on head and neck examination The subject should be seated comfortably and upright. Good general lighting and spot-lighting should be available to illuminate particular areas. A reflecting head-mirror with light source or pencil-torch will aid intra-oral inspection, and gloves should be worn for oral examination. Palpation varies according to the structure to be examined. It can involve using only the tip of one finger; or the pads of one, two or three fingers; or the pad of the thumb. A pinch grip can be made between finger and thumb. Structures such as bony points can be palpated with a simple touch. Others, such as bony ridges, require a massage-type movement or finger pads need to be dragged across them. Muscles are best demonstrated by putting them into action while resisting the movement they are producing. In this way, they may be seen under the skin or can be felt contracting. Small group activity is encouraged, in which one student acts as a model. However, some of the structures and procedures described can also be explored using self-examination. When examining radiographs (whether x-rays or scans), first note the plane in which they were taken; or, if 3D, the aspect taken of the head. A landmark such as a bony feature can be used to help identify further structures.

1

–2–

Bony landmarks A skull (complete with mandible and cervical skeleton) should be available for frequent crossreference to structures in the living subject as they are examined.

Anterior The subject is seated and facing forward. The two nasal bones that form the bony bridge of the nose are felt by pinching the nose firmly between the thumb and index finger and sliding them up and down the bridge. Feel where the bridge joins the forehead, which marks the nasion. The prominence in the forehead immediately above the nasion is the glabella. Deep to this is the frontal air sinus (Figure 2.1). The superciliary ridges extend laterally from the glabella, just above the upper margin of the orbit. To palpate the bony anterior nasal aperture, gently grip the soft tissues of the nostrils with the finger and thumb and push firmly backwards. The aperture presents as a sharp edge. If the S N I

M

Figure 2.1 Frontal x-ray of head showing air sinuses E = Ethmoids F = Frontal sinus O = Orbit M = Maxillary sinus

Figure 2.2 Frontal 3-dimensional CT reconstruction scan of skull S = Supraorbital foramen I = Infraorbital foramen M = Mental foramen N = Nasal bone

3

Living and Radiological Anatomy of the Head and Neck for Dental Students

pad of the thumb and middle finger are gently inserted into the nasal vestibules, one digit in each aperture, and then opposed, the anterior part of the nasal septum can be felt between them. It has a framework of cartilage which can be easily moved from side to side. The whole orbital margin is sharp and can be traced using the pad of the middle finger. Starting superiorly, the frontal bone is felt, then laterally the zygoma, followed by the maxilla inferiorly. The medial margin is formed by the lacrimal bone but is less distinct. Deeper pressure here brings the fingertip close to the ethmoid air cells on the medial wall.

Foramina on the face There are three foramina on the face (Figure 2.2) that can be palpated. They all lie on a vertical line touching the angle of the mouth. All are palpated using firm pressure with the pad of the index finger. The supraorbital foramen or notch lies on the superior orbital margin and close to the frontal air sinus. The infraorbital foramen is about 1cm below the inferior margin, on the facial surface of the maxilla. The maxillary air sinus lies immediately deep to this surface. The mental foramen lies about 1cm above the base of the mandible. Note that a cutaneous sensory branch of each division of the trigeminal (5th cranial) nerve emerges through the respective foramina. These are: the supraorbital nerve from the ophthalmic division, the infraorbital nerve from the maxillary division, and the mental nerve from the mandibular division. These nerves are confirmed by applying very firm pressure over the appropriate foramen (Figures 2.3 and 2.4), which causes pain. The final anterior landmark is the mental protuberance and this is palpable as a small prominence located in the midline, below the incisor teeth and adjacent gum on the body of the mandible.

Posterior

Figure 2.3 (far left) Palpating the supraorbital foramen Figure 2.4 (left) Palpating the infraorbital foramen

4

Bony landmarks

The subject is seated. The observer stands behind and the subject flexes the head downwards. Palpating in the midline over the occipital region using the pads of the index and middle finger, the prominence of the external occipital protuberance is located (Figure 2.7). This overlies the internal occipital protuberance and the location of the confluence of major intracranial venous sinuses. The superior nuchal line can be traced laterally from the external protuberance, running in a gentle curve towards the prominent mastoid process (Figures 2.5 and 2.6). The mastoid process is easily palpable behind the lobule of the auricle (Figure 2.8), where the sternomastoid muscle is attached. The line itself is clearly demarcated by noting the point at which the soft tissues on the back of the neck give way to the firmness of the occipital bone above them. The lambda is a point on the vault of the skull in the midline, about 7cm above the external protuberance. It marks the junction of the two parietal bones with the occipital, and can be palpated as a small depression using firm pressure.

Figure 2.5 Posterior 3D CT reconstruction of skull EO = External occipital protuberance NL = Superior nuchal line M = Mastoid process A = Posterior arch of atlas

Lateral Palpation can be carried out standing in front of or behind the subject. The best results are obtained using the pads of the index and middle fingers. The malar eminence (Figures 2.6 and 2.10) is the most prominent part of the cheek and is formed by the body of the zygoma. Firm pressure just below and anterior to the most prominent part may cause pain, due to compression of the zygomatico-facial branch of the zygomatic nerve. To palpate the zygomatic arch (Figures 2.6 and 2.9), the pads of the fingers are placed 4–5cm in front of the external auditory meatus and (using firm pressure) moved up and down over the arch. The upper and lower borders of the arch are also palpated. Above the arch is the depression of the temporal fossa (Figure 2.6), containing the temporalis muscle (see p. 35). The masseter muscle (see p. 34) lies in the depression below the arch and covers the ramus of the mandible. The

TF ZA Z M

N R A BM

Figure 2.6 Lateral 3D CT reconstruction of skull M = Mastoid process ZA = Zygomatic arch TF = Temporal fossa Z = Zygoma BM = Mandible base A = Angle R = Ramus N = Mandible neck

5

Living and Radiological Anatomy of the Head and Neck for Dental Students

frontal process of the zygoma can be located by palpating forwards along the upper border of the arch to a point where it suddenly turns upwards towards the vault of the skull. This angle marks the deepest part of the temporal fossa (Figure 2.6), where the temporalis muscle can be felt most easily.

Palpation of the mandible Palpation should start anteriorly at the chin and is best carried out by feeling the base (lower border) with the pads of the index and middle fingers (Figures 2.6 and 2.11) and sliding them backwards towards the angle of the ramus. Note that the base is quite thick, but as the angle is reached its lower border is much thinner (see Figure 5.6, p. 27). This is easily confirmed by gripping the base firmly between finger and thumb, first in the anterior part and then posteriorly near the angle. About 25 per cent of mandible fractures occur in this thin region. The angle of the mandible (Figure 2.12) is prominent and sharp. From here, upward palpation is made along the posterior border of the ramus towards the neck of the mandible. Finally, the mandible ramus is examined externally, using self-examination. The mouth is opened wide and, feeling through the skin of the cheek, the anterior border of the ramus is located. The ramus is then gripped between its anterior and posterior borders, using finger and thumb, and is confirmed as the mouth is opened and closed. 

Figure 2.7 Palpating the external occipital protuberance

6

Figure 2.8 Palpating the mastoid process

Bony landmarks

Figure 2.9 Palpating the zygomatic arch

Figure 2.10 Palpating the malar eminence

Figure 2.11 Palpating the base of the mandible

Figure 2.12 Palpating the angle of the mandible

7

–3–

Testing the cranial nerves Cranial nerve 1 – olfactory Olfactory function is tested by asking the subject to take a small sniff of a volatile liquid (e.g. vinegar or ammonia from a small container or a spray of perfume on a tissue) held below a nostril while the opposite side is closed (Figure 3.1). Remember that receptors are located in the olfactory epithelium in the highest part of the nasal cavity, below the cribriform plate of the ethmoid.

Figure 3.1 Testing the olfactory nerve

9

Living and Radiological Anatomy of the Head and Neck for Dental Students

Cranial nerve 2 – optic The tests used are very basic. Each eye is tested in turn, with the subject covering or closing one eye. Visual acuity is tested by asking the subject to read print on the page of a book. For greater accuracy a simple Snellen Test Chart as used by opticians can be used. Visual fields are tested with the subject seated and the examiner standing about 2 metres in front, holding a pencil or pen at eye level. The subject is asked to keep looking forward while the examiner moves the pen progressively, first laterally, then medially, then from above and finally from below. In each case, the examiner works slowly from the periphery towards the subject’s central visual axis. While performing each movement, the tip of the pen is agitated and the subject is asked to say when they first notice it moving. Three eye reflexes can be tested: corneal, light and accommodation. The corneal (blink) reflex is tested by lightly touching the cornea with the tip of a paper tissue, causing the eyelid to close. The sensory part of the reflex involves the ciliary branches of the nasociliary nerve from the ophthalmic division of cranial nerve 5. The motor part involves branches of cranial nerve 7 supplying the orbicularis oculi. In deep unconsciousness, the reflex is absent. The pupil light consensual reflex is tested by shining a bright light from a pencil torch into one eye (Figure 3.2). The pupil constricts in both eyes. This is because light falling on the illuminated retina is conducted along its optic nerve. However, on reaching the optic chiasma, some fibres pass into the optic tract on the same side, while others cross to the opposite tract. Each tract terminates in a lateral geniculate body (LGB), a lower visual centre in the midbrain. Stimulation of one retina therefore results in stimulation of both LGBs.

Figure 3.2 Testing pupil light reflex

10

Testing the cranial nerves

From the LGB, fibres pass to the adjacent Edinger Westphal parasympathetic nucleus. Outgoing fibres from this nucleus pass within the oculomotor nerve to synapse in the ciliary ganglion in the orbit. From the ganglion, ciliary nerves supply the sphincter pupillae and the ciliary muscle. The retina can be examined using an ophthalmoscope. This requires some practice and can be facilitated by examining the subject in a darkened room and using atropine eye drops to dilate the pupil. Features to note (Figure 3.3) include: the optic disc, which appears pale where the optic nerve enters; the red macula on its lateral side, where there is maximum concentration of cones concerned with activities requiring visual acuity, e.g. reading; and the retinal vessels, which radiate symmetrically from the optical disc.

Figure 3.3 Ophthalmoscopy of retina

The accommodation reflex test assesses the eye’s ability to adjust focus from distant vision to a near object, as when reading a book. The subject is asked to gaze at a distant object and then to suddenly focus with both eyes on a pencil or pen held close to the tip of the nose. This reflex has three components, two of which are visible. They involve the third cranial nerve and its parasympathetic fibres (see below). On each side, the pupil constricts and the eyes converge (adduct). Pupil constriction concentrates light on the macula and fovea in the centre of the retina, which has a high concentration of cones. Not visible is the contraction of the ciliary muscles innervated from the ciliary ganglion. These muscles relax the suspensory ligaments of the lens (allowing it to become more convex) and shorten the focal distance for viewing near objects. The third nerve nucleus is activated consciously from the cerebral cortex, through cortico-bulbar fibres which reach the third nerve nucleus in the midbrain.

11

Living and Radiological Anatomy of the Head and Neck for Dental Students

Cranial nerves 3 – oculomotor; 4 – trochlear; 6 – abducens These three nerves innervate the extraocular muscles, which anchor the eyeball to the posterior part of the orbit, to the roof and to the floor. They are responsible for moving the eyeball in several directions around vertical and horizontal axes. A pen or pencil is held in front of the subject. Starting in the midline, the subject is asked to look at the tip of the pen as it is moved slowly in different planes (Figure 3.4). The pen is first moved horizontally, from side to side; and then vertically, upwards and downwards. To test cranial nerve 3, the subject is asked to look medially (medial rectus) (Figure 3.4), downwards (inferior rectus) and upwards (superior rectus), also upwards and outwards (inferior oblique). To test cranial nerve 4, the subject is asked to look downwards and outwards (superior oblique). To test cranial nerve 6, the subject is asked to look laterally. A useful aid to memorising which nerves supply which muscles is the formula: LR6 SO4 + 3 = all others (This mimics the well-known basic chemical Figure 3.4 Testing extrinsic eye muscles formula for a sulphate.)

EB E

LR ON

T

TP

MR

P

C

O

12

Figure 3.5 Horizontal CT scan of head at level of orbits C = Cerebellum E = Ethmoid air cells EB = Eyeball LR = L ateral rectus MR = Medial rectus O = Occipital pole of cerebrum ON = Optic nerve P = Upper pons TP = Temporal pole T = Temporalis

Testing the cranial nerves

Cranial nerve 5 – trigeminal Of all the cranial nerves, the trigeminal nerve is the most important for the dental student since it is the major sensory nerve that innervates oral structures including the teeth, gums and tongue, and the muscles of mastication which move the mandible. It also innervates the temporomandibular joint. There are three divisions of the nerve: ophthalmic, maxillary and mandibular. The sensory component is tested by stimulating the cutaneous distribution of these nerves. The subject faces forward, closes their eyes and is told to respond when touched. For the ophthalmic division (frontal nerve), the skin is lightly stroked on the forehead (Figure 3.6); for the maxillary division (infraorbital nerve), above the mouth and below the orbit (Figure 3.7); and for the mandibular division (mental nerve), on the chin (Figure 3.8) lateral to the midline (mental nerve).

Figure 3.6 Testing the sensory facial distribution of the trigeminal nerve: Testing the ophthalmic division

Figure 3.7 Testing the sensory facial distribution of the trigeminal nerve: Testing the maxillary division

To test taste sensation conveyed in the lingual branch of the mandibular division, the subject protrudes the tongue while a few grains of sugar are deposited on the dorsum from a spatula (Figure 3.9). This is repeated using salt. Remember that the taste fibres are carried from the geniculate ganglion of the facial nerve in the petrous temporal bone, via the chorda tympani, which joins the lingual nerve in the infratemporal fossa.

13

Living and Radiological Anatomy of the Head and Neck for Dental Students

The motor component of the trigeminal nerve is carried in the mandibular division and supplies the muscles of mastication which move the mandible. These are considered with the temporomandibular joint.

Figure 3.8 Testing the sensory facial distribution of the trigeminal nerve: Testing the mandibular division

Figure 3.9 Testing the lingual branch of the trigeminal nerve

14

Testing the cranial nerves

Cranial nerve 7 – facial The major component of the facial nerve is motor, innervating the muscles of facial expression. In addition, these muscles have a protective function since they are arranged as sphincters and dilators around the major facial orifices – the eye and the mouth. The muscles are tested progressively. The frontalis is tested by asking the subject to look upwards and wrinkle their forehead. The orbicularis oculi, surrounding the eye, has two main parts. Within the eyelids, the palpebral part is tested by asking the subject to close their eyelids gently. The more extensive orbital part surrounds the orbital margins and is tested by asking the subject to screw their eyes up tightly (Figure 3.10). If these muscles are paralysed, the blink reflex is lost. This makes the eye more vulnerable to damage to the cornea. This damage may be caused by dryness and by foreign materials being retained on the conjunctiva covering the eye (instead of being wiped away by the eyelids). Transient facial nerve paralysis is a rare complication following inferior dental nerve block, either due to abnormal location of the facial nerve in the parotid gland or misdirected injection. To test the dilator muscles surrounding the mouth, the subject is asked to show their teeth (Figure 3.11). To test the sphincters closing the mouth, the subject is asked to purse the lips or whistle. It is important that the buccinator muscle is also tested, by asking the subject to pull in their cheek as when sucking (Figure 3.12). If the buccinator is paralysed, the subject may complain that food sticks in the mouth while they are swallowing. Figure 3.10 Testing the palpebral part of orbicularis oculi

Figure 3.11 Testing the dilators of buccal orifice

Figure 3.12 Testing the buccinator

15

Living and Radiological Anatomy of the Head and Neck for Dental Students

Cranial nerve 8 – cochlear-vestibular The test for the cochlear division is very simple. The subject is seated and the observer stands on one side about 2 metres away. The opposite ear is covered and the healthcare professional whispers a word or short phrase, which the subject repeats. Alternatively, the subject is asked to perform a simple task, such as raising their right hand. To test whether sound conduction through air is impaired, Rinne’s test can be used. The handle of a vibrating tuning fork (500Hz) is placed behind the ear, over the mastoid process. The subject listens and indicates when it can no longer be heard. The fork is then moved close to the auricle. If it can still be heard, air conduction is better than bone conduction to the inner ear. If it cannot be heard, air conduction is impaired. To test the static equilibrium component of the vestibular division (utricle and saccule), the subject closes their eyes and the healthcare professional, holding the subject’s head firmly between their hands, inclines it sideways and asks the subject to state the location of their head. To test the dynamic equilibrium component (semicircular canals), the subject closes their eyes while the examiner moves the subject’s head forwards and backwards, the subject stating the direction as the head is moved.

Cranial nerve 9 – glosso-pharyngeal This nerve is sensory to the oropharyngeal part of the tongue and pharyngeal wall. The subject tilts their head slightly backward and opens their mouth wide. The observer touches the back of the throat with the tip of a spatula to stimulate the gag reflex.

Cranial nerve 10 – vagus The subject opens the mouth wide and, while looking at the soft palate, the observer asks the subject to say ‘ah’. The soft palate should move upward, with the uvula in the midline. This does not test the parasympathetic part of the vagus but the axons from the nucleus ambiguus in the medulla which travel in the vagus. They supply striated muscle in the soft palate, pharynx, larynx and upper oesophagus – i.e. all the structures that have a function in swallowing.

Cranial nerve 11 – spinal accessory This nerve supplies the sternomastoid and trapezius muscles. To test the sternomastoid on one side, the subject is seated and instructed to turn their head towards the opposite side. Alternatively, they may be asked to flex the head forward towards the chest, while the movement is resisted by the examiner (Figure 3.13). To test the trapezius, the subject shrugs the shoulders upwards. While testing each of these muscles, the observer must actively resist the movement. The contracting muscles are then easily felt and seen.

16

Testing the cranial nerves

Figure 3.13 Testing the left sternomastoid muscle; turning the head to the opposite side is resisted

Cranial nerve 12 – hypoglossal This nerve supplies the muscles of the tongue which are classified into two groups: intrinsic and extrinsic. To test the intrinsic group which change the shape of the tongue, the subject is instructed to protrude the tongue and then roll it (Figure 3.14). Since tongue rolling is genetically based, some subjects cannot do this. To test the extrinsic group, the subject is asked to protrude the tongue, first in the midline and then to one side (Figure 3.15).

Figure 3.14 Testing the intrinsic muscles of the tongue

Figure 3.15 Testing the extrinsic muscles of the tongue (Note: The grey hue is due to filiform papillae clearly visible on the oropharyngeal part)

17

Living and Radiological Anatomy of the Head and Neck for Dental Students

To test elevation of the tongue, the subject is asked to touch the hard palate with the tip of the tongue. The muscle arrangement, location and relations of the tongue in the buccal cavity and oropharynx are clearly seen in a CT scan (Figure 3.16). Recall that the genio-glossus is the largest muscle and forms much of the tongue.

S C N P Figure 3.16 Sagittal CT scan of mouth

M

V H

18

E

G

C = Inferior concha E = Epiglottis G = Genio-glossus H = Hyoid bone M = Mandible N = Nasopharynx P = Hard palate S = Sphenoid air sinus V = Vallecula

–4–

Examining the buccal cavity and oropharynx The subject is seated, with their head tilted well back and their mouth open wide. A focusing lamp, reflecting head mirror and lamp, or pencil-torch provide a source of light.

Vestibule Using a spatula, the cheek and lips are displaced to expose the buccal vestibule (Figure 4.1) on each side, both superiorly and inferiorly. This is the space between the gums and cheeks or lips and allows inspection of gums and teeth. Normal gums are pink in colour due to the vascular mucosa. Teeth can be inspected for colour, number, spacing and shape. The subject is asked to grit their teeth to demonstrate normal Figure 4.1 Examining the buccal vestibule occlusion. Their number and classification by morphology should be reviewed and compared with their appearance on a dental planogram (Figure 4.2). In the upper vestibule on the (medial) alveolar side, deep palpation reveals shallow ridges in the gum due to underlying teeth Figure 4.2 Dental planogram (Note: Relate the number roots. Above this, the mucosa feels smooth and shape of teeth to the normal dental formula) over the facial surface of the maxilla, deep to which is the maxillary sinus. Note that the roots of molar teeth lie very close to the floor of the sinus (Figure 4.3). Faulty extraction may result in an oro-antral fistula.

19

Living and Radiological Anatomy of the Head and Neck for Dental Students

O

UD

MS

Figure 4.3 Sagittal CT scan of head (Note: close relation of teeth to maxillary sinus) M

Figure 4.4 The pterygomandibular raphe

Figure 4.5 Close-up of the pterygomandibular raphe

20

M = Mandible MS = Maxillary sinus O = Orbit UD = Upper dentition

In the lower vestibule immediately behind the lower third molar tooth is a conspicuous mucosal fold, which extends upwards to lie behind the upper third molar (Figure 4.4, 4.5). Using a fingertip, it is easily palpable as a tense band as the mouth is opened widely. This is the pterygomandibular raphe, and is an important landmark when anaesthetising the inferior alveolar nerve. Remember that this is the site of attachment to the buccinator muscle whose fibres sweep forwards into the cheek in the lateral wall of the vestibule. It is also the site of attachment to the superior constrictor muscle whose fibres sweep backwards into the lateral wall of the nasopharynx. The retromolar fossa of the mandible is palpable immediately behind the third molar tooth. If palpation is continued backwards and upwards from here, the lower part of the sharp anterior border of the ramus can be felt. Further upward palpation leads to the lower part of the

Examining the buccal cavity and oropharynx

S C N P

M

E

G V H

Figure 4.6 Sagittal CT scan of mouth C = Inferior concha E = Epiglottis G = Genio-glossus H = Hyoid bone M = Mandible N = Nasopharynx P = Hard palate S = Sphenoid air sinus V = Vallecula

coronoid process. Here the attachment of the temporalis can be felt when the mandible is raised. With firm lateral palpation behind the raphe, the medial side of the ramus can be felt but (due to the overlying fibres of the medial pterygoid muscle) it is not bony hard. It is in the space between the muscle and the ramus that local anaesthetic is injected to block the inferior dental nerve.

Tongue

Figure 4.7 Dorsum of tongue (Note: a grey V-shaped groove marks the junction of the smooth buccal and the more uneven pharyngeal part)

The tongue is a muscular organ that fills much of the buccal cavity. It lies below the hard palate which separates it from the nasal cavities (Figure 4.6) and above the floor of the mouth. Surface features can be easily examined on its dorsum and on its under-surface. To examine the dorsum, the mouth must be opened wide and the tongue protruded as far as possible. The anterior two-thirds is the most visible part and is located in the buccal cavity. It has a uniform greyish-pink colour (Figure 4.7) due to the filiform papillae which cover the whole surface. They give the tongue a furred appearance when it is dry. These are touch receptors. Dispersed among the papillae are small pink tastebuds (Figure 4.8), which are more numerous on the sides and tip of the tongue.

21

Living and Radiological Anatomy of the Head and Neck for Dental Students

Figure 4.8 Close-up of pink tastebuds on dorsum of the tongue

D F

Figure 4.9 Ventrum (undersurface) of tongue D = Opening of submandibular duct at side of frenulum F = Sublingual fold

22

The posterior third of the tongue is deeper and less visible. A shallow V-shaped groove (Figure 4.7) may be visible, separating the smooth buccal part of the tongue from the more irregular surface of the oropharyngeal part. The much larger circumvallate papillae also contain tastebuds and are arranged in a shallow V-shaped groove, separating the anterior visible part from the deeper posterior part. They are only visible if the deeper part of the tongue is strongly depressed with a spatula. To examine the under (ventral) surface of the tongue, the subject raises the tip to touch the roof of the mouth. A midline landmark is a fold, the frenulum, passing from the tongue to the floor of the mouth (Figure 4.9). If is too short, this can interfere with tongue movements (tongue-tie) and uncommonly may affect swallowing or speech. On each side of the frenulum, close to the floor of the mouth, is a small pink swelling. This is the opening of the duct of the submandibular gland which produces a mixed serous and mucous secretion. On both sides, at the junction of the tongue with the floor of the mouth, an elevated fold overlies the sublingual gland (Figure 4.9) which produces a mucous secretion. This gland has numerous ducts whose orifices are too small to see. Tributaries of the lingual veins are conspicuous through the thin mucosa.

Examining the buccal cavity and oropharynx

They provide a route for rapid absorption of drugs placed under the tongue. Note that the lingual vein drains into the internal jugular vein. To palpate the floor of the mouth (which contains the two mylohyoid muscles), a fingertip is carefully placed against the side of the frenulum. While pressing downwards, a finger of the opposite hand is placed on the skin of the submental region. By pressing upwards gently with this finger, at the same time as downwards with the finger in the mouth, movement between them can be easily detected.

Oropharynx The oropharynx is the posterior deeper part of the mouth and is less easy to examine. To facilitate this, the mouth must be wide open, the subject’s head tilted backwards and the tongue firmly depressed. A point source of light or reflecting head mirror is essential. The floor of the oropharynx is formed by the posterior basal part of the tongue. It lies behind the circumvallate papillae and its surface is smooth but slightly irregular, due to the presence of submucosal lymphoid tissue. The roof is the soft palate, which separates it from the nasal cavity. Its muscles include the levator and tensor palati, whose functions are to tense and elevate the soft palate when swallowing, to prevent reflux of food or fluids into the nose. The posterior edge is free and from it a midline landmark, the uvula, hangs over the dorsum of the tongue (Figure 4.10).

SP

T

U

PP PG Figure 4.10 Oropharynx PG = Palatoglossal fold PP = Palatopharyngeal fold SP = Soft palate T = Palatine tonsil U = Uvula

The lateral wall of the oropharynx is formed by a recess containing the palatine tonsil. The boundaries of the recess are marked by two mucosal folds: anterior and posterior. These folds contain muscles. In the posterior fold is the palatopharyngeus, while in the anterior is the palatoglossus. The paired palatoglossus muscles together form the oropharyngeal isthmus, which separates the oral cavity from the oropharynx. During swallowing, they contract like a sphincter to prevent food from refluxing back into the mouth.

23

Living and Radiological Anatomy of the Head and Neck for Dental Students

The posterior wall of the oropharynx is formed by constrictor muscles, covered by mucosa which may contain lymphoid nodules (Figure 4.11). The location of the oropharynx in relation to the nasal and laryngeal parts of the pharynx is shown in the CT scan of the head (Figure 4.12).

Figure 4.11 Lymphoid tissue on dorsum of oropharynx

MC IC

S NP OP PW LP

Figure 4.12 Sagittal CT scan of head

24

MC = Middle nasal concha IC = Inferior nasal concha NP = Nasopharynx OP = Oropharynx LP = Laryngopharynx PW = Posterior pharyngeal wall S = Sphenoid air sinus

–5–

Examining the arterial pulses, salivary glands and lymph nodes Arterial pulses The four arterial pulses can be located and they are best palpated using the pad of a single finger or thumb, rather than fingertips.

Common carotid The common carotid artery and its major divisions can be demonstrated radiologically by angiography (Figure 5.1) and by 3D reconstruction CT scans (Figure 5.2). The carotid is the most important pulse and essential to locate if a patient collapses unconscious. The pads of two fingers or the thumb are placed around the anterior border of the sternomastoid muscle (Figure 5.3) at the level of the cricoid cartilage, which is palpated in the midline of the neck at the level of the C6 vertebra. The muscle is slightly tensed by turning the head a little to the opposite side. The fingers are pressed firmly medially and deeply towards the side of the trachea.

EC CS B CC

Figure 5.1 Carotid angiogram

A

A = Aortic arch B = Bifurcation of common carotid artery CC = Common carotid artery CS = Carotid sinus at root of internal carotid artery EC = External carotid artery

25

Living and Radiological Anatomy of the Head and Neck for Dental Students

EC

CS

B CC

VA

Figure 5.2 A 3D reconstruction of a CT scan of carotid arteries and branches VA = Vertebral artery B = Bifurcation of common carotid artery CC = Common carotid artery CS = Carotid sinus at root of internal carotid artery EC = External carotid artery

Figure 5.3 Palpating the carotid pulse

Figure 5.4 Palpating the superficial temporal pulse Figure 5.5 Palpating the facial pulse

26

Examining the arterial pulses, salivary glands and lymph nodes

Superficial temporal The superficial temporal artery is felt immediately in front of the tragus of the ear (Figure 5.4) as it ascends across the posterior root of the zygomatic arch into the temporal fossa. It is easy to palpate and is an alternative to the carotid in an emergency. Note that it has ascended from the parotid gland where it arises as a terminal branch of the external carotid artery.

Facial To palpate this artery, the subject has to clench their jaw tightly to contract the masseter muscle. The pulse is felt at the anterior border of the masseter where the artery crosses the base of the mandible (Figure 5.5), having emerged from the submandibular gland.

Occipital This artery lies in a depression at the apex of the posterior triangle. Firm pressure is applied where the trapezius and sternomastoid muscles converge in a depression just below the occiput at the level of the superior nuchal line. It is an important source of blood supplying the scalp. Consequently, lacerations of the posterior scalp bleed freely.

Salivary glands There are three salivary glands, the largest of which is the parotid. This is a serous gland and produces about 20% of the the saliva. The superficial part is subcutaneous and lies just anterior to the external ear. It is normally impalpable but when enlarged produces a characteristic fullness of the face in front of the ear. The superficial part of the parotid continues behind the neck of the mandible, in front of the anterior border of the sternomastoid. It then extends deeply as far as the styloid process, which separates the gland from the carotid sheath that lies on the lateral pharyngeal wall. The location and extent of the parotid gland is visible radiologically using a CT scan T (Figure 5.6). The parotid duct can be palpated Ma F where it turns around the anterior border of M masseter (Figure 5.7) to pass deeply through R the bucccinator into the upper vestibule. EC

V P

ICA

IJV

Figure 5.6 Transverse CT scan of the head at the level of the parotid gland EC = External carotid artery F = Facial artery ICA = Internal carotid artery IJV = Internal jugular vein M = Masseter Ma = Base of mandible P = Parotid gland R = Ramus of mandible T = Tongue genioglossus V = Retromandibular vein

27

Living and Radiological Anatomy of the Head and Neck for Dental Students

Figure 5.8 Orifice of parotid duct in upper vestibule. Arrow indicates opening of parotid duct Figure 5.7 Palpation of parotid duct

Here its orifice is seen as a small elevation opposite the second upper molar (Figure 5.8). To locate the duct, the subject’s teeth must be clenched to tense the masseter. A fingertip is then drawn firmly down the anterior border until it flicks against the duct (Figure 5.7). This is about halfway between the zygomatic arch and the base of the mandible. The submandibular gland is a mixed serous and mucous gland. It is the major producer of saliva and it has two parts. The deep part lies on the upper surface of the mylohyoid muscle, in the floor of the mouth and close to the tongue. The superficial part lies below the mylohoid, under the base of the mandible. The duct enters the mouth below the tongue, on the side of the frenulum (see p. 22). The gland is not palpable unless it is enlarged. To locate it, the examiner stands behind the seated subject and feels below the base of the mandible for any enlargement and at the same time for submandibular lymph nodes (see below). The sublingual glands are described on p. 22. The duct system in the parotid and submandibular glands can be demonstrated by sialography, after injecting radio-opaque medium into the duct orifice (Figures 5.9a and 5.9b) through a cannula.

28

Examining the arterial pulses, salivary glands and lymph nodes

Figure 5.9 Sialograms (Note: the arrows mark site of insertion of cannula into opening of duct in buccal cavity)

a. Submandibular gland (lateral view)

b. Parotid gland (frontal view)

29

Living and Radiological Anatomy of the Head and Neck for Dental Students

Lymph nodes Usually lymph nodes are not palpable but it is important to know where to palpate them in case of enlargement. There are two groups of lymph nodes: superficial and deep.

Superficial lymph nodes These form a circle around the upper neck. They are best examined with the subject seated and the examiner standing behind, palpating progressively from anterior to posterior. Starting anteriorly beneath the chin, the submental nodes are located (Figure 5.10a); then the submandibular under the base of the mandible (Figure 5.10b), followed by the pre-auricular (parotid) nodes in front of the ear. Note that besides draining the facial region the submental and submandibular nodes drain intra-oral structures including the teeth, gums and tongue. Continuing the examination posteriorly, the post-auricular (mastoid) nodes are located behind the ear, over the mastoid area. Finally, the occipital node is located at the apex of the posterior triangle, in the region of the occipital artery (see p. 27). These two groups of nodes drain the back of the scalp.

Deep cervical nodes Unless they are considerably enlarged, the deep cervical nodes are not normally palpable because they lie deep to the sternomastoid muscle, along the course of the internal jugular vein. The superficial nodes drain into them. One of the deep nodes, the jugulo-digastric, is close to the angle of the mandible. It is of special interest because it drains the submental and submandibular nodes, as well as the posterior part of the tongue and oropharynx. It may become enlarged and palpable in pharyngitis and tonsillitis. The lowest of the deep cervical nodes are supraclavicular and located just above the middle third of the clavicle, at the base of the posterior triangle. They are not normally palpable.

Figure 5.10 Palpating the superficial ring of lymph nodes: a. Palpating the submental nodes (above left); b. Palpating the submandibular nodes (above right)

30

–6–

The temporomandibular joint (TMJ) and the muscles of mastication This important synovial joint is between the head of the mandible and the glenoid fossa of the temporal bone (Figures 6.1 and 6.2). It has an intra-articular disc which facilitates two main types of movement: simple hinge; and gliding forwards onto the articular eminence (Figure 6.3). Both movements can be easily seen when a thin-faced person is viewed from the side while chewing.

G

E ZA

EM

Figure 6.1 A 3D CT bony reconstruction of the TMJ (mouth closed)

N M

A AX SP

A = Atlas (C1) vertebra AX = Axis (C2) vertebra E = Articular eminence EM = External auditory meatus G = Head of mandible in glenoid fossa M = Mastoid process N = Neck of mandible SP = Styloid process ZA = Zygomatic arch

31

Living and Radiological Anatomy of the Head and Neck for Dental Students

G MF

H

Figure 6.2 Coronal CT scan of the head at the level of the TMJ TMJ

R

G = Glenoid fossa H = Mandible head MF = Middle cranial fossa R = Mandible ramus TMJ = Temporomandibular joint

G

E H

Figure 6.3 A 3D CT bony reconstruction of the TMJ (mouth open) E = Articular eminence G = Glenoid fossa H = Mandible head

32

The temporomandibular joint (TMJ) and the muscles of mastication

Figure 6.4 Examining the TMJ movement

Examination is made with the subject seated and most movements can be easily felt by selfexamination. The tip of an index finger is pressed very firmly, medially and slightly forwards, in the depression immediately below the external auditory meatus, between the mastoid process and the neck of the mandible (Figure 6.4). Initially, as the subject starts opening their mouth, slight movement of the neck is felt. This is hinge movement. To feel the gliding movement, firm forward pressure is maintained and the subject is asked to open their mouth as wide as possible when the neck is felt to move forwards. Bennett movement occurs in each TMJ when the mandible moves to one side, as when chewing. To detect Bennett movement, the examiner stands behind the subject and (using both hands) first palpates the posterior border of the ramus on each side, then moves the fingers upwards to feel the mandibular neck on each side. While the examiner maintains firm pressure upwards and forwards, the subject opens their mouth – first in the midline and then while moving the mandible to one side. In the TMJ, on the side opposite to the direction in which the jaw is moving, greater movement is felt, involving both hinge and gliding with some rotation. This compares with less movement in the TMJ on the side towards which the mandible is moving, where the head remains in the glenoid recess and much of the movement of the head is rotation about a vertical axis. The morphology of the head and the glenoid fossa reflect the mandible’s adaptation to sideto-side movements during chewing. The glenoid fossae lie slightly oblique in relation to the transverse axis (Figure 6.5), as does the head of the mandible (Figure 6.6), confirming their adaption to rotation movements when chewing.

33

Living and Radiological Anatomy of the Head and Neck for Dental Students

Figure 6.5 Horizontal CT scan of head at level of TMJ PCF

Ma EAM

H M

E

L

E = Articular eminence EAM = External auditory meatus H = Mandible head in glenoid fossa L = Lateral pterygoid plate M = Medial pterygoid plate Ma = Mastoid air cells PCF = Posterior cranial fossa G Note: 1) Transverse plane of head is oblique compared to transverse anatomical plane c.f. Figure 6.6 2) Lateral pterygoid plate is large reflecting attachment of pterygoids and points laterally reflecting direction of pterygoids

TMJ movements and associated muscles The movements of the TMJ are: elevation (closing mouth); depression (opening mouth); protrusion (chin pushing forward); retrusion (chin retracting); and side-to-side. During testing, the subject sits upright. When assessing the various muscles, the integrity of their nerve supply from the mandibular division of the fifth cranial nerve is also being tested. Muscles are best demonstrated by resisting the movement they produce. They can be tested by self-examination.

Masseter

Figure 6.6 A 3D CT bony reconstruction of mandible Note: The transverse axis of each mandible head lies oblliquely in relation to the anatomical transverse axis around which elevation and depression occur

34

This muscle elevates the mandible and assists protrusion. It attaches to the zygomatic arch and to the lateral side of the mandibular ramus (Figure 6.7). To feel it contract, the examiner places the pads of two fingers over the ramus of the mandible on each side, just above and anterior

The temporomandibular joint (TMJ) and the muscles of mastication

Figure 6.7 (left) Coronal CT scan through the head at the level of the TMJ L = Lateral pterygoid M = Medial pterygoid Ma = Masseter Figure 6.8 (below) Testing elevators of mandibleJ

L

M

Ma

to the angle. When the subject clenches the jaw tightly, the muscles are felt to tense. The subject is also asked to open their mouth, and then to close it against resistance, while the examiner presses firmly down on the chin (Figure 6.8).

Temporalis

T

Figure 6.9 Coronal CT scan through the head at the level of the zygomatic arch T = temporalis

This muscle is used in elevation and retraction. It has extensive attachment to the temporal fossa and to the coronoid process of the mandible (Figure 6.9). It can be palpated on each side, using the pads of three fingers placed over the deepest part of the temporal fossa. This lies above the anterior part of the zygomatic arch, in the angle between it and the temporal process of the zygoma. On clenching the jaw firmly, the muscle can be felt to tense but not as forcibly as the masseter, since the temporalis is covered by the strong temporal fascia.

35

Living and Radiological Anatomy of the Head and Neck for Dental Students

Digastric and mylohyoid These muscles depress the mandible. The mylohoid forms the floor of the mouth. The pad of the thumb is pressed firmly upwards, just behind the chin, while the subject opens their mouth as wide as possible against strong resistance (Figures 6.10, 6.11). The submental region can be felt to tense. It can also be felt to tense during swallowing when it contracts to push the tongue upwards towards the palate. At the same time, whilst swallowing, if the tips of the greater horns of the hyoid bone (see p. 37) are gripped between forefinger and thumb, upward movement is felt – due to the attachment of these muscles.

Pterygoids There are two pterygoid muscles: lateral and medial. Both are attached to the lateral pterygoid plate (Figure 6.5, p. 34). The medial pterygoid attaches to the medial side of the mandibular ramus, while the lateral pterygoid attaches to the neck of the mandible and capsule of the TMJ (Figure 6.7, p. 35). The lateral also acts to open the mouth and protrude the mandible. The medial muscle, in particular, produces side-to-side movement. To test the pterygoids, the subject attempts to move the mandible well to one side, against strong Figures 6.10, 6.11 Testing depressors of mandible manual resistance applied to the mandible (Figure 6.12).

Figure 6.12 Testing pterygoid muscles

36

–7–

Neck landmarks The neck can be examined from three aspects: anteriorly, laterally and posteriorly.

Anterior aspect Several midline structures can be palpated. The subject is seated, facing forward. The head must be tilted backward to make the structures more prominent.

Hyoid bone This is located in the upper part of the neck, at about the level of the base of the mandible and the C3 vertebra. The index finger and thumb are widely separated and then the pads of each are closed to grip the side of the throat firmly but gently (Figure 7.1). The tips of the greater horns can be felt and confirmed by rocking the hyoid from side to side. When the subject swallows, the hyoid can be felt to move upwards, as the mylohyoid muscles contract in the floor of the mouth. Figure 7.1 Palpating hyoid bone

Thyroid cartilage This cartilage is initially identified by feeling for the midline thyroid notch, which lies at the upper part of the laryngeal prominence, where the two laminae join. The laminae can be gripped between the finger and thumb in order to move the larynx from side to side (Figure 7.2). It is more extensive than the hyoid and lies at the level of the C4 and C5 vertebrae. When the subject swallows, the thyroid cartilage can be felt and seen to move upwards, due to the contraction of the inferior constrictor muscles of the pharynx which are attached to the thyroid laminae.

Figure 7.2 Palpating thyroid cartilage

37

Living and Radiological Anatomy of the Head and Neck for Dental Students

Cricoid cartilage The cricoid cartilage is mostly enclosed within the thyroid cartilage (Figure 7.3) except for the anterior arch, which is located just below the thyroid cartilage. The cricoid arch is quite narrow and lies at the level of the C6 vertebra, which marks the junction of the larynx with the trachea, and the pharynx with the oesophagus. To feel the arch, keeping in the midline, the tip of the index finger is guided off the lower border of the thyroid cartilage into a narrow depression. Immediately below it is the anterior arch of the cricoid, over which the finger can be rolled (Figure 7.3). Beneath this midline depression, between the thyroid and cricoid cartilages, lies the cricothyroid ligament. This is clinically significant in an emergency when a patient is choking. As a last resort, a quick incision through the skin and underlying ligament (a cricothyroidotomy) can relieve the airway, since it is below Figure 7.3 Palpating cricoid cartilage the level of the glottis.

Trachea Palpating progressively the neck in the midline between the cricoid and suprasternal notch tracheal rings can be felt as a series of small ridges. If a stethoscope is placed in the midline, just above the suprasternal notch, typical twophase bronchial breath sounds can be clearly heard (Figure 7.4). These can be compared with much quieter vesicular breathing, with the stethoscope placed over the posterior triangle above the middle third of the clavicle. Here also pulsations of the subclavian artery may be heard. A transverse CT scan of the neck (Figure 7.5) clearly shows the thyroid and cricoid cartilages and closely related structures. Figure 7.4 (right) Auscultation of trachea

38

Neck landmarks

T

C SM A IJV CA

Figure 7.5 Transverse CT scan of neck at level C5

N Tr

A = Airway (subglottic) C = Cricoid cartilage CA = Common carotid artery IJV = Internal jugular vein N = Nuchal erector spinae muscles SM = Sternomastoid T = Thyroid cartilage Tr = Trapezius

Lateral aspect The sternomastoid muscle is an important landmark, which separates the anterior from the posterior triangle. It is considered on p. 42. The external jugular vein descends downwards and laterally over the muscle to cross its posterior border just above the clavicle, where it passes deeply to enter the subclavian vein. The external jugular vein lies superficially under the skin and can be demonstrated by the subject pinching their nose tightly while trying to blow forcibly down their nose, with their mouth closed (Valsalva manoeuvre). This raises intrathoracic pressure and impedes venous return, causing thin-walled veins in the neck to distend.

Posterior aspect The subject is seated and facing forward. In the lower part of the neck the contour curves downwards and laterally to the shoulder region. This is due to the underlying trapezius muscle, which is considered on p. 42. To test the upper fibres, the examiner stands behind the subject and places one hand on each shoulder. The subject is asked to shrug their shoulders upwards, while downward pressure is applied to the shoulders. To test the middle fibres, the subject is asked to brace the shoulders backwards, which is resisted by pressure applied behind the shoulder on each side. Deep to the trapezius muscle on each side of the midline is a thick column of muscles, which reach as far as the superior nuchal line on the occipital bone. The column can be gripped between fingers and thumb. These are the strong anti-gravity nuchal muscles that keep the head upright and

39

Living and Radiological Anatomy of the Head and Neck for Dental Students

bend the head backwards. They can be demonstrated by placing a hand over the occipital region and resisting attempts to extend the head backwards. A groove can be felt in the midline between the two extensor columns. The lower part is shallow, and at the lowest point the spinous process of the C7 vertebra is conspicuous. It can be easily palpated, particularly if the head is flexed forwards. This is the vertebra prominens. When the upper part of the groove is palpated, it is felt to deepen as the fingertip is guided upwards to reach the external occipital protuberance of the occipital bone. In the depth of the groove is the free edge of the strong elastic ligamentum nuchae.

40

–8–

Joints and movements of the head and neck The cervical spine forms the core of the neck (Figure 8.1) and is the most mobile part of the vertebral column. At the upper end, the first two vertebrae, the atlas and axis, are specially adapted (Figure 8.2) to allow purposeful head movements.

A

Figure 8.1 A CT 3D reconstruction scan of skull and cervical spine

Ax F

IVD

A Ax F IVD

= Atlas posterior arch = A xis spinous process = Facet joint = Intervertebral disc

41

Living and Radiological Anatomy of the Head and Neck for Dental Students

L A M S O

Figure 8.2 Transverse CT scan of neck level of C1 vertebra (Note: The scan also shows bilateral facial fractures of the maxilla) A = Anterior arch of atlas L = Lateral pterygoid plate M = Medial pterygoid O = Odontoid process (dens) of axis S = Tip of styloid process

Testing head movements The subject should be seated and facing forward. Movements can be demonstrated either passively with the examiner holding the head and moving it, or actively with the examiner resisting movements (Figures 8.3, 8.4, 8.5 and 8.6). Flexion and extension are tested in the sagittal plane: flexion by resisting forward movement by putting pressure against the forehead; and extension by resisting backward movement by putting pressure on the occiput. Remember that the prime head flexors are the sternomastoid muscles; and the extensors are the trapezius muscle, together with the splenius and powerful extensor nuchal antigravity muscles (the upper part of the erector spinae group), which keep the head upright. Figure 8.3 Resisting head flexion

42

Testing the cranial nerves

Figure 8.4 Active full head flexion

Figure 8.5 Active head extension

Lateral flexion is tested by asking the subject to tilt the head sideways towards one shoulder. These movements occur between the occipital condyles and the upper articular facets of the atlas. Side-to-side (lateral) movements of the head can be tested passively or by pressing against the side of the head while the subject tries to turn it to that side. This movement occurs between the atlas and the axis and involves the facet joints, together with the midline pivot joint, between the dens of the axis and anterior arch of the atlas (Figure 8.2). In everyday language, by turning the head from side to side, one says ‘No’ at the atlanto-axial joints; and by nodding up and down, one says ‘Yes’ at the atlanto-occipital joints, between the atlas and the occipital condyles!

Figure 8.6 Active lateral head rotation

43

–9–

The scalp, ear and eye Scalp The scalp covers the cranial vault of the skull. It extends from the forehead backwards, as far as the upper part of the neck, at the level of the superior nuchal line. Its five layers can be conveniently remembered using the letters in the word SCALP. The outermost layer is Skin which is moderately thick and contains sweat and sebaceous glands, as well as a variable amount of hair follicles. The second layer is thick Connective tissue and the third is formed by the Aponeurosis of the occipitofrontalis muscle. The fourth layer, Loose connective tissue, is easily demonstrated in the living subject since it allows mobility of the scalp. The deepest layer is the very thin Pericranium which adheres strongly to the cranial bones. The thin fourth layer is clinically important, since it is this layer that gives way when the scalp is violently torn off the head – in avulsion scalping injuries. To examine mobility, the subject is seated while the examiner stands over them and spreads the fingers and thumb of one hand widely apart and then closes them to firmly grip the front or side of the scalp (Figure 9.1). By repeating this several times as though massaging the hair with shampoo, the scalp can easily be felt to move over the underlying bony vault. The frontalis muscle, part of the third layer, wrinkles the skin of the forehead and is tested by asking the subject to look upward, while keeping their head facing forward. Figure 9.1 Testing layer 4 of the scalp

45

Living and Radiological Anatomy of the Head and Neck for Dental Students

Ear Of the three parts of the ear, external, middle and inner, only the external is accessible for living anatomy examination. It consists of the auricle (pinna) and the external auditory canal. The framework of the auricle is elastic cartilage. This is demonstrated by gripping the subject’s auricle and displacing it forward and then releasing it. The pinna recoils to its original position. Skin covers the cartilage and is more adherent to the front than the back of the pinna. To confirm this, pinch up the skin on each side of the ear. Anteriorly, at the root of the auricle, is a prominence called the tragus (Figure 9.2), and below this is a notch that leads to the dependent lobule. This varies in size but its core is fat, not cartilage. Confirm this by pinching it between finger and thumb. The margins of the auricle are framed by the rim-like helix. The external auditory canal passes inwards from the depths of the auricle. It is lined with skin containing ceruminous glands which secrete wax. The outer part is elastic cartilage which is continuous with that of the pinna. The deep part Figure 9.2 The auricle is bony, comprising the tympanic plate and the squamous part of the temporal bone. You can confirm this by examining a skull. In the depths of the auditory canal is the tympanic membrane. To examine it, the subject is seated facing forward; the examiner then grips the upper posterior part of the auricle, pulling it M upwards and backwards. This converts the canal from a curved into a straight passage, allowing the examiner to introduce the speculum of an L auroscope and guide it carefully down towards TM the ear drum. The normal healthy drum appears pearly white with the light reflecting from the lower part (‘light reflex’). Usually the outermost auditory Figure 9.3 Tympanic membrane ossicle, the malleus and its handle are visible deep L = light reflex to the drum (Figure 9.3). M = handle of malleus TM = edge of tympanic membrane

46

The scalp, ear and eye

Eye The anterior one-fifth of the eyeball can be examined, together with the overlying eyelids. The observations are best made by students working in pairs, observing each other’s eyes, using good illumination such as a pencil torch.

Eyeball A diagram of a sagittal section through the eye should be available during the examination. Observe the following structures: 1) The white of the eye is the sclera (Figure 9.4) and forms its outer layer. Small blood vessels are often visible in the sclera, close to the junction with the eyelids. Anterior to the sclera is the transparent cornea, through which light enters the eye. Deep to the cornea is the anterior chamber containing aqueous humour. 2) The iris, which is coloured brown, blue or green, surrounds the central pupil and contains sphincter and dilator muscles which control its size (see pupil light reflex, p. 10. 3) Immediately behind the iris is the lens. The pupil is black and is the aperture through which light reaches the retina deep inside the eyeball. It appears black because all light entering the eye is absorbed and not reflected. Also, the retina itself has a dark pigment layer of light-absorbing melanin.

Eyelids

P I S

C

F O

Figure 9.4 Eyelid and conjunctival fornix C = Caruncle F = Conjunctiva fornix I = Iris S = Sclera O = Opening of lacrimal canaliculus P = pupil

Since they are closely applied to the anterior surface of the eyeball, the eyelids provide effective protective shields for the eye. Confirm that they are covered by loose skin by pinching it up and seeing that eyelashes project from their free edges. Note that when fluid (oedema) accumulates in the soft tissues under the skin, the eyes appear ‘puffy’. Using a fingertip, depress the lower lid so that the space between the inner surface of the eyelid and eyeball is opened up (Figure 9.4). This space is called the lower fornix and is lined by conjunctiva that covers the eyeball and the eyelid. Tear fluid passes here as it is guided towards the medial canthus of the eye for drainage. Foreign bodies (such as dust) may lodge in either the upper or lower fornix.

47

Living and Radiological Anatomy of the Head and Neck for Dental Students

Finally, depress the lower lid close to its medial end to reveal a pink triangular area called the lacus lacrimalis. In the centre of this is a small pink nodule called the caruncle, which contains glands that produce an oily secretion. Close to the lateral side of the caruncle, look for a small pale spot with a central opening (Figure 9.4). This is the lacrimal punctum and entrance to the lacrimal canaliculus which drains tear fluid into the lacrimal sac, close to the medial canthus. From the lacrimal sac, tear fluid passes down the nasolacrimal duct into the inferior meatus of the nose.

48

Further reading

Further reading Csillag, A. (1999). Anatomy of the living human: Atlas of medical imaging. Konemann UK Ltd. Kelley, L.L. & Petersen, C. (2012). Sectional anatomy for imaging professionals. 3rd edn. Mosby Elsevier. Lumley, J.S.P. (2008). Surface anatomy: the anatomical basis of clinical examination. 4th edn. Churchill Livingstone. Standring, S. (2015). Gray’s Anatomy. 41st edn. Elsevier.

49

Living and Radiological Anatomy of the Head and Neck for Dental Students

Index abducens nerve 12 accommodation reflex test 11 arterial pulses 25, 26 auditory canal, external 46 auricle 46 Bennett movement 33 bony landmarks 3–7 buccal vestibule 19, 20 caruncle 48 cervical spine 41 cochlear-vestibular nerve 16 common carotid artery 25, 26 cornea 47 cricoid cartilage 38 cricothyroid ligament 38 dental planogram 19 digastric muscle 36 ear 46 eye 47 eye reflexes 10 eyeball 47 eyelids 47 facial artery 27 facial nerve 15 foramina 3, 4 fornix 47 frenulum 22 frontal air sinus 3 frontalis muscle 45 glabella 3 glenoid fossa 33 glosso-pharyngeal nerve 16 head and neck examination 1 head movements, testing 42, 43 hyoid bone 37 hypoglossal nerve 17

50

inferior alveolar nerve 20 iris 47 lacrimal punctum 48 lambda 5 lens 47 ligamentum nuchae 40 local anaesthetic 21 lymph nodes 30 malar eminence 5, 7 mandible 6, 7 masseter 34 mastoid process 5 mouth 18 muscles of TMJ 34 muscles, examination of 1, 15 mylohyoid muscle 36 nasal aperture 3 nasal bones 3 nasion 3 neck 37, 41 nerves, cranial 9–18 nuchal muscles 39 occipital artery 27 occipital protuberance, external 5, 40 oculomotor nerve 12 olfactory nerve 9 optic nerve 10 orbital margin 4 oropharynx 23, 24 palatine tonsil 23 palpation 1 parotid gland 27 pterygoid muscles 36 pterygomandibular raphe 20 retina 11 retromolar fossa 20 Rinne’s test 16

salivary glands 27 scalp 45 sclera 47 skull 3–6 soft palate 23 spinal accessory nerve 16 sternomastoid muscle 39 sublingual glands 22, 28 submandibular gland 28 superciliary ridges 3 superficial temporal artery 26, 27 superior nuchal line 5 tastebuds 21 temporal fossa 5 temporalis muscle 35 temporomandibular joint (TMJ) 31, 33, 34 temporomandibular joint, movements of the 34 thyroid cartilage 37 tongue 21, 22 trachea 38 tragus 46 trapezius muscle 39 trigeminal nerve 4, 13, 14 trochlear nerve 12 tympanic membrane 46 vagus nerve 16 Valsalva manoeuvre 39 vertebra prominens 40 visual acuity 10 visual fields 10 zygomatic arch 5, 7