THE ANGULAR TRACT: AN ANATOMICAL

Transcription

1 British Journal of Oral Surgery (1981) 19, The British Association of Oral Surgeons X/81/ $02.00 THE ANGULAR TRACT: AN ANATOMICAL OF SURGICAL SIGNIFICANCE STRUCTURE HAITHEM A. ZIARAH, B.D.s., M.MED.SCI.~ and MARTIN E. ATKINSON, B.SC., PH.D.~* IDepartment of Dental Surgery, University of Shefield; adepartment of Human Biology and Anatomy, University of Shefield, Shefield SIO 2TN Summary. During the course of anatomical studies of the submandibular region, the presence of a strong fascial band running deep from the investing fascia to the fascia of the posterior belly of the digastric was repeatedly encountered. This angular tract is described in detail. Its position as a division between the submandibular gland and lower portion of the parotid gland suggests that the tract is potentially useful as a landmark and as protection for the glands and their contents in submandibular surgical approaches. Introduction In the course of anatomical studies of the nerves in the submandibular region (Ziarah & Atkinson, 1981a and b) we repeatedly observed a thick fascial band passing from the angle of the mandible to the hyoid bone. The position of this band makes it particularly important in the surgery of the submandibular gland and the submandibular region in general and therefore merits consideration. The fascial band we observed corresponds to the tractus angularis or pars angularis fasciae cervi as illustrated by Pernkopf (1963) and to the angular tract briefly mentioned by Seward (1968). Despite these previous references to its presence no detailed description has been made before and is presented below. Materials and methods Observations were made from 110 facial halves obtained from cadavers which had been hard-injected with a mixture of formalin, glycerine, alcohol and carbolic acid through the common carotid artery or femoral artery or both. Results As the outer lamina of the investing fascia of the neck is removed a thickened band of fascia is encountered on its deep surface (Fig. 1). The band runs obliquely in both the sagittal and coronal planes. It extends from the angle of the mandible above and runs downwards and backwards to the greater cornu of the hyoid bone below. The superficial edge blends with the investing fascia and the deep edge is placed more anteriorly and blends with the fascial sheaths of the posterior belly of the digastric muscle and stylohyoid muscle. The anterior surface which faces obliquely anterolaterally passes in its upper part behind and deep to the posterior pole of superficial lobe of the submandibular gland. The posterior surface which faces obliquely posteromedially overlies the lower pole of the parotid gland superiorly (Fig. 1). Essentially (Received 30 September 1980; accepted 18 October 1980) * For offprints. 116

2 SURGICAL SIGNIFICANCE OF THE ANGULAR TRACT 117 FIG. 1. A dissection showing the angular tract (A). The platysma muscle (PM) and outer layer of the investing fascia (f) have been retracted postero-inferiorly. The facial artery (a) is indicated and the tip of the periosteal elevator lies over the gonion. P indicates the parotid compartment below the lower pole of the parotid gland (L) reflected superiorly. the thickened fascial band separates the two major salivary glands and their related structures in the neck (Fig. 2). The angular fascial band was present in every facial half examined as a tough fascial band. Discussion Following the precedent set by Pernkopf (1963) and Seward (1968) the most suitable name for this thickened deep extension of the investing fascia is the angular tract. When Seward (1968) mentioned the angular tract in connection with a submandibular approach to the submandibular gland he saw it as a surgical hazard with possibilities of instruments being deflected deeply by the tough fascia towards the external carotid artery and internal jugular vein. This is unlikely to happen due to its deep attachment to the fascial sheaths of the muscles which will protect the carotid sheath and its contents. Although bearing in mind Seward s (1968) warning we take an opposing view and see the angular tract as an aid to submandibular surgery and not a hindrance.

3 118 BRITISH JOURNAL OF ORAL SURGERY FIG. 2. Another dissection showing the angular tract (A) separating the parotid compartment (P) from the posterior part of the submandibular gland (S). The platysma muscle (PM) and investing fascia (f) have been reflected postero-inferiorly and the tip of the periosteal elevator lies over the gonion. Essentially the obliquely orientated angular tract divides the area immediately below the posterior part of the body of the mandible into an anterior submandibular compartment and a posterior parotid compartment. By dissecting anterior or posterior to the angular tract, as the individual case dictates, the other compartment can be left undisturbed and free from any damage. Access to the parotid compartment can best be achieved by incising the investing fascia immediately anterior to the sternocleidomastoid fascia, due consideration being taken of the course of the mandibular and cervical nerves during initial placement of the incision (Ziarah & Atkinson, 1981a and b). Once the investing fascia is incised posterior to the angular tract, a distinct surgical pocket is created (Fig. 2). The boundaries of this pocket are, Anteriorly. Above is the angle of the mandible and its associated musculature and from this and passing down to the hyoid bone is the angular tract. Posteriorly. The sternocleidomastoid fascia. Medially. The fascia covering the stylohyoid and posterior belly of the digastric muscles. Laterally. The parotid fascia on the deep side of the lower portion of the parotid gland and its contents and the investing layer of the deep cervical fascia.

4 SURGICAL SIGNIFICANCE OF THE ANGULAR TRACT 119 The only contents in this pocket are one or two lrenae communicantes which may be dealt with by the standard surgical procedures. The submandibular gland, facial artery and anterior facial vein lie anterior to the angular tract and the cervical and mandibular branches of the facial nerve may be retracted within the fascia-muscle-skin flap. The angle of the mandible is exposed for manipulation or for further exposure by subperiosteal dissection (Fig, 3). There is no corresponding pocket in the submandibular compartment but access to the mandibular body and submandibular gland can be achieved by utilising a plane of dissection deep to the investing fascia and anterior to the angular tract. The facial artery and anterior facial vein are present in this plane but again can be dealt with using standard surgical techniques. The angular tract may be exposed by dividing the investing fascia from its attachment to the hyoid bone and providing dissection is carried out anterior to the tract the parotid gland and the emerging cervical and mandibular branches of the facial nerve are protected from damage. The nerves lie superficial to the plane of dissection and are therefore also protected (Ziarah & Atkinson, 198la and b). FIG. 3. The division, above the hyoid bone (H), of the neck into a parotid compartment and subman dibular compartment (S) by the angular tract (A). M indicates the mandibular body, V the IJed of the anterior facial vein and PM the platysma muscle reflected anteriorly.

5 120 BRITISH JOURNAL OF ORAL SURGERY If the whole hemimandible needs to be exposed the two compartments can be brought into continuity by detaching the angular tract from its inferior insertion into the hyoid bone and its deep insertion into the fascia of the stylohyoid and posterior belly of digastric. As the tract is reflected superiorly the lower pole of the parotid gland is carried with it by virtue of the obliquity of the angular tract and is safe from the field of operation. Thus the knowledge of the presence and precise relations of the angular tract has potential use in submandibular surgical approaches. We wish to thank Professor R. Barer for provision of facilities in the Department of Human Biology and Anatomy and Messrs G. Hibbard and D. Hinchliffe for technical assistance. We also thank Messrs R. Cousins and Mr Turton for preparation of the illustrations and Professor P. A. Bramley for his help and advice. Pernkopf, E. (1963). An atlas of topographic and applied human anatomy. Volume 1, Head and Neck. Philadelphia: Saunders. Seward, G. R. (1968). Anatomic surgery for salivary calculi. IV. Calculi in the intraglandular part of the submandibular duct. Oral Surgery, Oral Medicine and Oral Pathology, 25, 670. Ziarah, H. A. &Atkinson, M. E. (1981a). The surgical anatomy of the mandibular distribution of the facial nerve. British Journal of Oral Surgery, Vol. 19, No. 3 (in press). Ziarah, H. A. & Atkinson, M. E. (1981b). The surgical anatomy of the cervical distribution of the facial nerve. British Journal of Oral Surgery, Vol. 19, No. 3 (in press).