THE SURGICAL ANATOMY OF THE CERVICAL DISTRIBUTION OF THE FACIAL NERVE. Biology and Anatomy, University of Shefield

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1 British Journal of Oral Surgery (1981), 19, The British Association of Oral Surgeons X/81/ $02.00 THE SURGICAL ANATOMY OF THE CERVICAL DISTRIBUTION OF THE FACIAL NERVE HAITHEM A. ZIARAH, B.D.s., M.MED. sc1.1 and MARTIN E. ATKINSON, B.SC., PH.D.~* 1 Department of Dental Surgery, University of Shefield; 2 Department of Human Biology and Anatomy, University of Shefield Summary. In an attempt to improve the safety of the submandibular approach to the mandible and submandibular gland anatomical dissections of 110 facial halves were undertaken. Observations were made on the course of the cervical branch of the facial nerve in relation to bony and soft tissue landmarks and fascial planes. The course of the nerve and its relation to the platysma muscle and investing fascia dictate the placement and depth of incision used for the submandibular approach. Introduction Surgical access to the body and ascending ramus of the mandible and the submandibular gland is often obtained through the submandibular region of the neck. The lower branches of the facial nerve are often encountered during this approach and damage to these nerves results in paralysis of the lower lip and angle of the mouth producing an ugly cosmetic deformity. Attention has mainly been directed to the marginal mandibular branches of the facial nerve and all standard surgical texts and most articles on the subject make some comment on its course and relevance. However, comparatively little has been published on the detailed anatomy (Dingman & Grabb, 1962; Ziarah & Atkinson, 1981a & b). Even less has been published about the cervical branch. Apart from descriptions in the standard texts it hardly receives mention. The reasons for this are probably that the cervical branch only supplies the platysma muscle which is regarded as an insignificant muscle of facial expression. Indeed it is often regarded more as a superficial muscle of the neck. However electromyographical studies by de Sousa (1964) have shown that the platysma muscle has a significant action on the corner of the mouth. Ellenbogen (1979) has suggested that it is damage to the nerve supply of the platysma which causes pseudoparalysis, mimicking paralysis of the mandibular branch, after platysmal face-lift operations; the pseudoparalysis profoundly affects the ability to smile, albeit only temporarily, although the full denture smile is never restored. Thus the action of the platysma and integrity of its nerve supply are more significant than generally realised. The anatomy of the cervical branch of the facial nerve has not been the subject of detailed study but the standard textbooks generally agree that it is a single branch passing deep to the platysma muscle and lying some distance below the inferior border of the mandible. Anderson (1978), however, claims the cervical branch crosses the jaw to anastomose with the mandibular branches of the facial nerve and help supply the muscles of the lower lip and chin. (Received 30 September 1980; accepted 19 December 1980) * Address for correspondence and reprint requests: Dr M. E. Atkinson, Department of Human Biology and Anatomy, University of Sheffield, Sheffield SlO 2TN. 171

2 172 BRITISH JOURNAL OF ORAL SURGERY In view of the increasing attention to the significance of the platysma muscle and its nerve supply and the paucity of information on the anatomy we undertook a study of the anatomy of the nerve in cadaveric material. Materials and methods A total of 110 facial halves from hard injected cadavers were examined. All subjects were fixed with dentures in place where worn, and the mouth closed. The age and sex distribution of subjects is shown in Table I. Table I Age and Sex Distribution of Subjects Sex Age distribution Number Male Female Totals In view of the scant attention given to the cervical nerve in surgical papers and texts a series of mock operations were carried out on an additional six cadavers by one of our colleagues. The operations performed were the submandibular approach to the ascending ramus (Risden, 1934), the exposure of the mandibular body (Dingman & Grabb, 1962), the exposure of the whole 1976) and three submandibular approaches to the submandibular gland (Seward, 1968; Patey, 1969; Rankow & Polayes, 1976). After completion of the mock operations the cadavers were dissected to ascertain the damage to the cervical nerve and related structures. Results The cervical branch of the facial nerve left the antero-inferior border of the lower pole of the parotid gland in company with the mandibular branch (Fig. 1). The two nerves diverged from each other at a variable distance from the gland but had always separated from each other by the time they had reached the angle of the mandible. The cervical branch always lay just posterior to the mandibular branches and rarely anastomosed with them (Ziarah & Atkinson, 1981b). The cervical nerve emerged from the parotid as a single branch in 80 per cent of the facial halves studied and passed posterior to the angle of the mandible but was never observed to cross it (Fig. 1). The nerve lay an average horizontal distance of 0.83 cm posterior to the gonion with a range of cm as ascertained from measurements on the dissected cadavers (Fig. 2). When the nerve reached the posterior aspect of the superficial surface of the submandibular gland it divided into several slender branches supplying the platysma muscle. In the remaining 20 per cent of facial halves the nerve emerged as two closely related branches which ran parallel to each other until they reached the submandibular gland where they diverged to form a fine plexus anterior to the hyoid bone (Fig. 3).

3 SURGICAL ANATOMY OF THE CERVICAL NERVE FIG. 1. The parotid gland opened to demonstrate the emerging cervical (c) and mandibular (m) nerves. Note their relationship to each other and the mandibular angle (M). The cervical nerve in this specimen is a single nerve. The nerves whether single or double trunks passed through the neck above the level of the hyoid bone before dividing into their terminal plexuses. The whole course of the nerves, whether single or double, lay in a plane deep to platysma but superficial to the outer lamina of the investing layer of the deep cervical fascia and formed a fine plexus on the underside of the muscle anterior to the hyoid bone (Fig. 4). Although anastomoses with the mandibular branch of the facial nerve were rarely seen, anastomoses with the transverse cervical and great auricular nerves of the cervical plexus were frequent. An ascending branch curved up from the transverse cervical nerves at the tip of the greater cornu of the hyoid bone to communicate with the cervical branch of the facial nerve to form a nerve trunk of substantial thickness 1913-B

4 174 BRITISH JOURNAL OF ORAL SURGERY Number Facial Halves of PO Distance (cm) FIG. 2. The distance between gonion and the distal branch of the cervicofacial nerve (Gn-Cn). Number of facial halves: 50 Mean: 0.83 k 0.37 cm Range: cm division of the facial (Fig. 5). Another ascending branch of the transverse cervical nerve was also seen in several facial halves which arose near the origin of the transverse cervical nerves as they appeared around the posterior border of the sternocleido-mastoid muscle. This branch ran just posterior to the emerging cervical branch of the facial nerve (Fig. 4), entered the substance of the parotid gland and communicated with the cervical branch of the seventh nerve just within the gland. A similar ascending branch which entered the parotid parenchyma arose from the anterior of the two branches of the great auricular nerve and again communicated with the cervical branch of the facial nerve in the gland substance. These latter two branches of the cervical plexus could easily be confused with the cervical branch of the facial nerve unless careful dissection was undertaken to ascertain their origin and connections; a luxury available in the dissecting room but not in the operating theatre. The results of the mock operation were revealing. After the Risden (1934) approach further dissection showed that the cervical branch of the facial nerve was cut through in two places. Firstly, it had been cut through about the level of the hyoid and retracted with the platysma and secondly, it was severed near its emergence from the parotid gland and this proximal stump had been retracted with the gland. Following Seward s (1968) approach to the submandibular gland it was found that the cervical branch of the facial nerve had been cut through in the posterior part of the incision. Again using the Rankow and Polayes (1976) approach the cervical branch was

5 SURGICAL ANATOMY OF THE CERVICAL NERVE 175 F IG. 3. A close-up photograph to show the bifurcation of the cervical nerve (dotted lines) near the gonion (G). The platysma muscle (PM) has been reflected. severed as it crossed the posterior portion of the submandibular gland. In this subject the nerve was double and both branches had been cut. Using the approaches advocated by Stell (1976) for the hemimandible and Patey (1969) for the submandibular gland no injury to the cervical branch of the facial nerve was observed. Discussion The apparent neglect of the surgical anatomy of the cervical branch of the facial nerve is probably due to the fact that it only supplies the platysma muscle and the clinical effect of damage to the nerve will therefore be less noticeable. However the importance of the platysma in mouth opening and smiling has recently been pointed out by Ellenbogen (1979). The cervical nerves are in general of greater diameter than the adjacent mandibular branches of the facial nerve especially after receiving the ascending communicating branch of the transverse cervical nerves at the greater cornu of the hyoid. The nerve branches could only be followed as far as the level of the body of the hyoid at which point they divided into fine plexuses which were difficult to trace to their termination by gross observation. Nevertheless the plexus appeared to be limited to the platysma

6 176 BRITISH JOURNAL OF ORAL SURGERY FIG. 4. A dissection showing anastomotic branches of the great auricular nerve (GA) entering the parotid glznd posterior to the emerging cervical nerve (Ce). The anastomotic branch (dotted) of the transverse cervical nerve (TC) is also visible. The transverse cervical nerve continues into the skin (S) and the thicker cervical nerve distal to the anastomosis spreads out deep to the platysma muscle (PM). muscle and we found no evidence to suggest that they cross the mandible to supply the depressors of lip as described by Anderson (1978). Although anastomoses between the cervical branch of the facial and the transverse cervical nerves have been described previously (Warwick & Williams, 1973) the communicating branches of the transverse cervical nerves which enter the parotid gland parenchyma have not been mentioned before. Again, the communication between the great auricular nerve and cervical branch of the facial nerve has been described previously (Warwick & Williams, 1973). The significance of these communications remains in doubt but it is known that the cervical plexus is the terminal afferent pathway for proprioceptive fibres from the sternocleidomastoid and trapezius muscles (Warwick & Williams, 1973) and muscles of the tongue (Fitzgerald & Sachithanandan, 1979). Possibly these branches carry proprioceptive fibres from the muscles of facial expression, the route of which is uncertain at present (Barr, 1979). In common with the mandibular branches of the facial nerve in the neck (Ziarah & Atkinson, 1981b) the cervical branches run in a plane superficial to the investing layer of the deep cervical fascia and deep to the platysma muscle. Surgical anatomy As we have shown by carrying out operations on cadaveric subjects some standard submandibular approaches jeopardise the integrity of the cervical branch of the facial nerve, which can lead to pseudoparalysis of the lower lip (Ellenbogen, 1979). Submandibular surgical approaches should therefore be designated to preserve the cervical branches if at all possible.

7 SURGICAL ANATOMY OF THE CERVICAL NERVE 177 FIG. 5. A dissection showing anastomosis between the transverse cervical nerve (t) and the cervical branch of the facial nerve (c). Note the thickness of the cervical branch distal to the anastomosis compared with the mandibular branches (m) above it. Within the parotid gland and around the mandibular angle the mandibular and cervical branches of the facial nerve are in close proximity therefore remarks applying to the mandibular nerve (Ziarah & Atkinson, 1981b) apply equally well to the cervical nerve in this region. To briefly reiterate our previous findings, incisions placed 2 cm clear of the gonion will preserve the parotid pole and its contained nerves and the proximal extracranial branches of the nerves as they emerge from the gland. In a previous study we designated a danger zone for the mandibular branches of the facial nerve (Ziarah & Atkinson, 1981b); an area within which incision or dissection could jeopardise the nerve. These boundaries can be extended to delineate a similar danger zone for the cervical nerve (Fig. 6). The posterior and anterior landmarks for the zone are identical for the mandibular

8 178 BRITISH JOURNAL OF ORAL SURGERY FIG. 6. The extension of the danger area of the mandibular nerve (cross-hatched) to include the corresponding area for the cervical nerve (open circles). H-H indicates the position of the hyoid bone and the figures are centimetre measurements from landmarks referred to in the text. and cervical branches but inferiorly the zone is extended obliquely downwards to 3 cm below the mandibular angle and 4 cm below the mandibular notch then extending forward at this level to vertically below the premolar tooth. In practice it will be found that the inferior limits of the danger zone correspond to the hyoid bone which, of course, is readily palpable. Incisions along or outside these boundaries will preserve the integrity of the main trunks of the cervical and mandibular branches of the facial nerve. Incisions should be carried deep to the investing layer of the cervical fascia to which the nerves lie superficial. This depth obviates the need to dissect the nerves and in fact they are not encountered during operation. The nerves, together with the lower pole of the parotid gland can be safely retracted with the investing fascia. Ellenbogen

9 SURGICAL ANATOMY OF THE CERVICAL NERVE 179 (1979) has suggested that dissection on the deep surface of platysma is responsible for damage to fine terminal branches of the nerve. Again, by dissecting deep to the fascia even those fine fibres will be afforded some protection. Acknowledgements The authors wish to thank Professor P. A. Bramley for suggesting this study and for his help and encouragement. Professor R. Barer was kind enough to place facilities in his department at our disposal. We also wish to thank Messrs G. Hibbard and D. Hinchliffe for technical assistance in the dissecting room, many medical, dental and speech science students for their co-operation and Mr R. Cousins and Mr M. Turton for preparation of illustrations. Finally, we wish to thank Mr J. V. Townend for carrying out the mock operations. References Anderson, J. E. (Editor) (1978). Grant s Atlas of Anatomy, 7th Ed., Figs Baltimore: Williams & Wilkins. Barr, M. L. (1979). The Human Nervous System. An anatomic viewpoint, 3rd Ed., p Maryland: Harper & Row. de Sousa, 0. M. (1964). Estudo electromiographicofico dom platysma. Foblia Clinical Biology (Brazil) 33, 42. (Cited by Barmajian, J. V. (1978). Muscles Alive, 4th Ed., p Baltimore: Williams & Wilkins). Dingman, R. 0. & Grabb, W. C. (1962). Surgical anatomy of the mandibular ramus of the facial nerve based on the dissection of 100 facial halves. Plastic and Reconstructive Surgery, 29, 266. Ellenbogen, R. (1979). Pseudo-paralysis of the mandibular branch of the facial nerve after platysmal face-lift operation. Plastic and Reconstructive Surgery, 63, 364. Fitzgerald, M. J. T. & Sachithanandan, S. R. (1979). The structure and source of lingual proprioceptors in the monkey. Journal of Anatomy, 128, 523. Patey, D. H. (1969). In: C. Rob & R. Smith (Editors), Operative Surgery, Vol. 6, 2nd Ed., p London: Butterworth. Rankow, R. & Polayes, I. (1976). Diseases of the salivary glands, p Philadelphia: Saunders. Risden, F. E. (1934). Ankylosis of the temporo-maxillary joint. Journal of the American Dental Association, 21, Seward, G. R. (1968). Anatomic surgery for salivary calculi Part IV. Calculi in the intraglandular part of the submandibular duct. Oral Surgery, Oral Medicine and Oral Pathology, 25, 674. Stell, D. M. (1976). Nose and Throat. In C. Rob & R. Smith (Editors), Operative Surgery, 3rd Ed., pp London : Butterworths. Warwick, R. & Williams, P. L. (1973). Gray s Anatomy, 35th Ed., pp & Edinburgh: Longmans. Ziarah, H. A. & Atkinson, M. E. (1981a). The angular tract: an important anatomical structure of surgical significance. British Journal of Oral Surgery, 19, 116. Ziarah, H. A. &Atkinson, M. E. (1981b). The surgical anatomy of the mandibular distribution of the facial nerve. British Journal of Oral Surgery, 19, 159.