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Surgical Anatomy of the Neck
Surgical Anatomy of the Neck HARVEY W. BAKER, M.D., F.A.C.S.*
There is an abundance of detailed information on the applied anatomy of the neck. Rather than attempt to duplicate this material it will be the author's purpose to point out the structures encountered in areas of the neck entered most frequently by the general surgeon. The experience of assisting many generations of surgical residents has taught the author that there are several areas where dissection may be difficult for the uninitiated and where important structures may be damaged. Rather than "surgical anatomy of the neck," this section might well be entitled "how to avoid trouble in the neck."
GENERAL CONSIDERATIONS
The anatomy of the neck is remarkably constant and, once the surgeon gains familiarity with it, important structures may be anticipated, readily identified and preserved. In few surgical fields are clean anatomic dissection, careful hemostasis and wide exposure of more importance, for it is by these measures that operative problems and complications are avoided. While an earlier generation of surgeons performed marvelous feats with local infiltration or nerve block anesthesia, it is the author's conviction that for adequate exposure and safety, most operations on the neck should now be performed under general anesthesia, preferably with an endotracheal tube in place. Exceptions to this principle may be made for the excision of skin lesions, epidermoid cysts and a few other minor conditions. All too frequently, however, an anticipated "minor" procedure in the neck with local anesthesia suddenly becomes a major problem. The author has witnessed and helped control serious hemorrhage during scalene lymph node biopsies under local anesthesia, has noted spinal accessory nerve damage following excision of lymph nodes in the posterior cervical triangle, From the Department of Surgery, University of Oregon Medical School, Portland, Oregon * Clinical Associate in Surgery, University of Oregon Medical School
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and has frequently found that removal of a "superficial" lesion leads one into contact with important deep structures. Positioning of the patient in the head-up or reverse Trendelenburg position is of value. This improves venous drainage and aids in exposure. The slightly increased risk of air embolism if a major vein is entered has thus far been only theoretical. Exposure is also facilitated by extension of the neck by means of a pad or small sandbag beneath the shoulders and by turning the head far to the unaffected side. Generously long incisions allowing adequate exposure for the task at hand are important. Keloid formation is rather uncommon in the neck and well planned incisions are seldom unsightly. The skin lines of the neck run generally in a transverse fashion and incisions are best when they conform. A useful incision in the upper neck commences below the mastoid and curves downward and forward toward the tip of the thyroid cartilage. A slightly curved transverse incision 2 cm. below and parallel to the body of the mandible gives excellent exposure to the submandibular region and seldom results in a noticeable scar. The standard collar incision for thyroid surgery or an outward extension of this paralleling the clavicle is useful in the lower neck. For major problems and the widest exposure, however, an oblique incision along the anterior margin of the sternocleidomastoid muscle gives maximum safety. This can be carried if need be from the mastoid process to the sternum and horizontal extensions may be made along the mandible and the clavicle from the upper and lower ends. While this oblique incision does not conform to skin lines, it is the safest for extensive procedures and the resulting scar is usually acceptable .
THE DIGASTRIC TRIANGLE (Fig. 1)
This triangle of the neck, bounded by the edge of the mandible and the anterior and posterior bellies of the digastric muscle, must be entered for excision of the submaxillary salivary gland or lymph nodes about it, for exposure of the mandible, and as part of a radical neck dissection or suprahyoid dissection. As the area is approached, usually through a transverse submandibular incision, one must look for the mandibular branch of the facial nerve. This tiny filament courses horizontally beneath the platysma and upon or in the underlying fascial layer, a varying distance of 0.5 to 2 cm. below the mandible. The nerve crosses superficial to the facial artery and accompanying anterior facial vein below the point where they cross the notch of the mandible. A bit posterior to this, a cervical branch of the nerve may be seen extending downward in the neck before the nerve itself disappears upward into the parotid. Anteriorly, before reaching the insertion of the digastric, the nerve curves upward over the edge of the mandible. This nerve is frequently difficult to identify. A helpful maneuver is to observe the corner of the mouth while sweeping the
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handle of the scalpel from the midpoint of the mandible downward on the neck. The lip will twitch as the nerve is crossed. Injury to this nerve results in paralysis of the lower lip on the involved side; fortunately in many instances there will be recovery, through anastomosing branches of the facial nerve. After the mandibular branch has been identified, and by dissection beneath it gently swept up to safety over the mandible, the superior border of the digastric triangle may be defined. A transverse incision is made on the lower free edge of the mandible commencing just back of the insertion of the anterior belly of the digastric. As the incision is carried down to bone, the contents of the triangle are bluntly pushed downward. Near the midpoint of the mandible, the facial artery and anterior facial vein must be divided. After freeing the superior border of the triangle, the anterior belly of the digastric is next exposed by sharp dissection. The submaxillary
Figure 1. The digastric triangle.
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salivary gland frequently bulges out of the triangle over the anterior belly of the digastric, but it is easily elevated as the muscle is followed downward from the mandible to its tendinous portion on the hyoid bone. The key to successful dissection from this point on is identification of the free posterior edge of the mylohyoid muscle. Failure to locate and retract this anatomical landmark leads to troublesome bleeding and possible injury to important structures. Dissection is commenced anteriorly in the acute angle formed by the mandible and the anterior belly of the digastric. Areolar tissues and one annoying small artery are divided as the mylohyoid is exposed. Dissection is then carried out directly upon the muscle, sweeping areolar tissue, lymph nodes, and an overhanging portion of the submaxillary gland posteriorly. At length a vertical free edge of the muscle is reached and success is at hand. A small retractor is used to retract the mylohyoid forward, exposing the floor of the digastric triangle formed by the hyoglossus. The submaxillary gland is pulled downward; this brings the large lingual nerve into view since it is attached to the gland by small nerve twigs (submaxillary ganglion). When this attachment is divided the lingual nerve again ascends behind the mandible. The submaxillary gland may now be rotated downward and Wharton's duct is identified, extending anteriorly and upward toward the floor of the mouth. The hypoglossal nerve becomes visible coursing obliquely upward and anteriorly upon the hypoglossus muscle. A fairly large lingual vein lies on either side of the hypoglossal nerve and bleeding is avoided by bluntly sweeping the submaxillary gland away from the floor of the triangle. The contents of the digastric triangle are now pulled posteriorly to complete the dissection as attention is directed to the posterior belly of the digastric. As this muscle is exposed the last remaining important structure is visualized. The facial artery which had been divided above at the mandible, enters the triangle posteriorly and inferiorly as it ascends beneath the posterior belly of the digastric to course along the deep surface of the submaxillary gland. It is a fairly large vessel as it enters the triangle just a short distance from its origin from the external carotid, and it must be carefully secured. Once the artery has been divided, dissection of the digastric triangle can be rapidly completed.
THE STERNOMASTOID OR CAROTID REGION (Fig. 2)
The broad sternocleidomastoid muscle covers a large portion of the lateral cervical region. Beneath it lie the carotid sheath and numerous important structures. A wide variety of surgical conditions require exposure of all or part of this area. These include branchial cleft cysts and sinuses, the important deep jugular lymph nodes, lesions of the carotid artery, neurogenic tumors, deep abscesses and pharyngeal diverticula. This zone
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must also be traversed for exposure of the anterior surface of the cervical spine. The key to successful dissection in this region is wide exposure and then retraction of the anterior margin of the sternocleidomastoid muscle. The outline of the muscle is easily noted by inspection and palpation of the neck. After the platysma and investing fascial layers are incised, the anterior margin of the muscle is isolated for as great a distance as the incision will allow and is then retracted posteriorly. As the fascia over the muscle is incised in the upper third of the neck, care must be taken to avoid injury to the great auricular nerve. This nerve, originating from 0-2 and 0-3, passes around the posterior border of the sternocleidomastoid"f1an d
Figure 2.
The sternomastoid or carotid region.
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curves forward and upward toward the ear, lying close to the anterior margin of the muscle. Injury to the nerve results in an annoying anesthesia of the lobe and posterior surface of the ear. The upper portion of the external jugular vein after its exit from the parotid lies close to the great auricular nerve. As the upper third of the sternomastoid is retracted the carotid sheath comes into view. This fascial layer is gently spread to expose the internal jugular vein which passes upward to disappear beneath the posterior belly of the digastric muscle. An important group of lymph nodes, the deep jugular nodes, lie along the course of the vein. A node or group of nodes lying upon the vein just inferior to the posterior belly of the digastric (subdigastric nodes) are among the first to be involved by metastatic cancer from the tongue, tonsil or pharynx. Further exposure in the upper carotid region requires identification and division of the common facial vein, a large tributary of the internal jugular. This vein extends anteriorly and upward from its junction with the jugular toward the submandibular region where it is formed by the confluence of the anterior and posterior facial veins. Just before its union with the jugular, the common facial may be joined by the superior thyroid and lingual veins. When the common facial vein is divided, the internal jugular may be retracted posteriorly for identification of deeper structures. The common carotid artery is located deep to the internal jugular vein. As the carotid is exposed, the vagus nerve must be identified; it lies on the surface of the carotid and accompanies the internal carotid above the bifurcation. The bifurcation of the artery is somewhat variable in position but generally lies opposite the superior margin of the thyroid cartilage. The superior thyroid artery is readily identified arising anteriorly from the external carotid near the origin of that vessel. The superior thyroid may originate so close to the carotid bifurcation that ligation of the external carotid artery requires preliminary ligation and division of the superior thyroid. A short distance above the carotid bifurcation the hypoglossal nerve must be identified for safe dissection in this region. This nerve descends from the skull between the internal jugular vein and internal carotid artery. As it emerges beneath the posterior belly of the digastric muscle, the nerve curves forward crossing the external carotid, giving off the descendens hypoglossi as it does so. The hypoglossal nerve is most easily identified at the point where it crosses the external carotid to course anteriorly and again dip beneath the digastric to enter the digastric triangle. It must be gently elevated for wide exposure of the external carotid. Two important structures lie deep to the carotid bifurcation, one a bit posteriorly and the other extending anteriorly. The posterior deep aspect of the artery is in close relation to the cervical sympathetic chain which lies upon the prevertebral fascia. The superior cervical ganglion may
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be identified as a bulbous swelling of the chain a short distance above the carotid bifurcation. Injury to the chain results in Horner's syndrome and unilateral absence of sweating of the face. Extending anteriorly beneath the carotid bifurcation is the superior laryngeal branch of the vagus nerve. This nerve leaves the vagus at the nodose ganglion located just below the jugular foramen. It passes deep to the carotid and curves forward beneath the superior thyroid artery, dividing into two branches to supply the larynx. Injury to this nerve results in partial anesthesia of the larynx, often with aspiration of food and saliva. One other structure must occasionally be identified in the upper carotid region. This is the spinal accessory nerve which upon leaving the jugular foramen crosses the internal jugular vein obliquely to extend downward and posteriorly in the neck. The nerve is usually obscured in areolar tissue close to the deep posterior surface of the sternocleidomastoid and it gives off a branch to the muscle, about 4 cm. below the mastoid process. It then enters the posterior cervical triangle which it traverses to reach the trapezius. The accessory nerve may be injured in the upper carotid region during excision of a branchial cleft cyst. Such cysts typically lie upon the carotid sheath beneath the upper third of the sternocleidomastoid. The deep posterior surface of the cyst is in close proximity to the accessory nerve. The lower carotid region has less complex anatomical relations. Exposure is again obtained by identifying and retracting the anterior margin of the sternocleidomastoid muscle. As this is accomplished the omohyoid muscle immediately comes into view as it crosses the carotid sheath obliquely behind the sternomastoid to ascend vertically with the prethyroid muscles. The omohyoid must be divided for adequate exposure. Division should be accomplished with care since the deep surface of the omohyoid lies immediately upon the internal jugular vein. Further exposure is afforded by division of the middle thyroid vein which courses transversely from the thyroid gland to the internal jugular. Once this is accomplished the carotid sheath may be retracted laterally and the larynx retracted medially for ready exposure of the prevertebral fascia, the bodies of the cervical vertebrae, and the esophagus. Only one additional structure, the inferior thyroid artery, crosses this plane rather low in the neck. This vessel emerges beneath the carotid sheath to reach the posterior aspect of the thyroid gland. It must usually be divided for adequate exposure and delivery of a pharyngoesophageal diverticulum. When the artery is divided, the larynx may be rotated to better expose the posterior surface of the thyroid and the esophagus. The recurrent laryngeal nerve can usually be identified entering the larynx just behind the cricothyroid articulation. Blunt dissection can be carried freely upward in the plane between the esophagus and the cervical vertebrae as high as the nasopharynx.
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THE SUPRACLAVICULAR REGION AND POSTERIOR TRIANGLE (Fig. 3)
This large compartment of the neck is bound by the middle third of the clavicle, the trapezius, and the posterior margin of the sternocleidomastoid. The prevertebral fascia covering the scalene muscles forms the floor of the triangle; there is direct communication with the mediastinum inferiorly and the axilla laterally. The space must be entered for lesions of the brachial plexus and subclavian artery, for removal of cervical ribs, for lymph node biopsy, and as part of a bloc dissection of the neck. In approaching this region the only important superficial structure to be encountered is the external jugular vein. This vessel courses beneath the platysma from the midportion of the sternocleidomastoid vertically toward the clavicle where it dips inward to join the subclavian vein. After the external jugular is divided and the investing layer of deep fascia incised the omohyoid muscle is seen to form a prominent landmark. It extends from the posterior corner of the triangle obliquely upward a variable distance above the clavicle to pass beneath the sternocleidomastoid and over the carotid sheath. The point at which the omohyoid emerges beneath the clavicle and the lower border of the trapezius forms the lower posterior boundary of a radical neck dissection. The omohyoid is enveloped by the pretracheal fascia which then extends inferiorly behind the clavicle to enclose the subclavian vein. When this fascial layer is incised one enters a plane in direct communication with the mediastinum and must identify a number of vital structures. The carotid sheath lies most medially in the supraclavicular region beneath the clavicular head of the sternocleidomastoid, which must be retracted or divided for adequate exposure. The junction of the internal jugular and subclavian veins is usually beneath the clavicle; occasionally, however, the subclavian vein may rise above the clavicle when the neck is extended. Immediately lateral to the jugular vein is the thoracic duct on the left and the right lymphatic duct on the right. These thin-walled lymphatic vessels ascend into the neck from the mediastinum, passing upward behind the carotid artery and jugular vein, and then arch downward to the lateral aspect of each jugular-subclavian junction. A vertically ascending jugular trunk may be seen joining each major lymph vessel and occasionally a subclavian trunk can be seen extending laterally. While ligation of the thoracic duct or right lymphatic duct may be performed with safety, undetected injury to either of these structures is followed by profuse lymph drainage which frequently requires operative treatment. Lateral to the carotid sheath and major lymphatic ducts is an important group of inferior deep cervical lymph nodes (scalene nodes) which lie grouped in loose areolar and fatty tissue. These nodes communicate with the deep jugular nodes above and serve as drainage areas for the mediastinum and infraclavicular viscera as well. Coursing transversely in this same region are transverse cervical and suprascapular arteries and veins.
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These vessels may be the source of troublesome bleeding during radical neck dissection or scalene lymph node biopsy. The arteries originate from the thyrocervical trunk of the subclavian artery or may arise independently from,the subclavian. They emerge on the medial edge of the scalenus anticus muscle and curve laterally to cross the lower neck, roughly parallel to the clavicle. Excessive traction on these vessels may avulse them from their subclavian origin. The scalenus anticus muscle lies beneath the scalene lymph nodes and extends between the subclavian vein and artery to insert on the first rib. The phrenic nerve is easily identified on the surface of the scalenus anticus; it is the only structure that passes in a medial direction as it descends in the neck. The subclavian artery beneath the scalenus anticus may take a
Trans. cervical a.
Figure 3.
Thyrocervical a.
The supraclavicular region and posterior triangle.
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surprisingly high curve up into the cervical region before dipping behind the clavicle laterally. As dissection is carried lateral to the scalene lymph nodes, the brachial plexus may be exposed beneath loose areolar and fatty tissue and beneath the transverse cervical and suprascapular vessels. The trunks of the brachial plexus emerge between the scalenus anticus and medius muscles and course obliquely downward and laterally to pass beneath the clavicle. Both the brachial plexus and subclavian artery may be elevated by a cervical rib; the artery may be compressed by the overlying scalenus anticus in this situation.
SUMMARY Important structures which may be encountered in many of the common surgical procedures in the neck have been described. Safe surgery in this region depends on a detailed knowledge of the anatomy, wide exposure, and careful hemostasis. 2250 N.W. Flanders Street Portland, Oregon 97210
There is an abundance of detailed information on the applied anatomy of the neck. Rather than attempt to duplicate this material it will be the author's purpose to point out the structures encountered in areas of the neck entered most frequently by the general surgeon. The experience of assisting many generations of surgical residents has taught the author that there are several areas where dissection may be difficult for the uninitiated and where important structures may be damaged. Rather than "surgical anatomy of the neck," this section might well be entitled "how to avoid trouble in the neck."
GENERAL CONSIDERATIONS
The anatomy of the neck is remarkably constant and, once the surgeon gains familiarity with it, important structures may be anticipated, readily identified and preserved. In few surgical fields are clean anatomic dissection, careful hemostasis and wide exposure of more importance, for it is by these measures that operative problems and complications are avoided. While an earlier generation of surgeons performed marvelous feats with local infiltration or nerve block anesthesia, it is the author's conviction that for adequate exposure and safety, most operations on the neck should now be performed under general anesthesia, preferably with an endotracheal tube in place. Exceptions to this principle may be made for the excision of skin lesions, epidermoid cysts and a few other minor conditions. All too frequently, however, an anticipated "minor" procedure in the neck with local anesthesia suddenly becomes a major problem. The author has witnessed and helped control serious hemorrhage during scalene lymph node biopsies under local anesthesia, has noted spinal accessory nerve damage following excision of lymph nodes in the posterior cervical triangle, From the Department of Surgery, University of Oregon Medical School, Portland, Oregon * Clinical Associate in Surgery, University of Oregon Medical School
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and has frequently found that removal of a "superficial" lesion leads one into contact with important deep structures. Positioning of the patient in the head-up or reverse Trendelenburg position is of value. This improves venous drainage and aids in exposure. The slightly increased risk of air embolism if a major vein is entered has thus far been only theoretical. Exposure is also facilitated by extension of the neck by means of a pad or small sandbag beneath the shoulders and by turning the head far to the unaffected side. Generously long incisions allowing adequate exposure for the task at hand are important. Keloid formation is rather uncommon in the neck and well planned incisions are seldom unsightly. The skin lines of the neck run generally in a transverse fashion and incisions are best when they conform. A useful incision in the upper neck commences below the mastoid and curves downward and forward toward the tip of the thyroid cartilage. A slightly curved transverse incision 2 cm. below and parallel to the body of the mandible gives excellent exposure to the submandibular region and seldom results in a noticeable scar. The standard collar incision for thyroid surgery or an outward extension of this paralleling the clavicle is useful in the lower neck. For major problems and the widest exposure, however, an oblique incision along the anterior margin of the sternocleidomastoid muscle gives maximum safety. This can be carried if need be from the mastoid process to the sternum and horizontal extensions may be made along the mandible and the clavicle from the upper and lower ends. While this oblique incision does not conform to skin lines, it is the safest for extensive procedures and the resulting scar is usually acceptable .
THE DIGASTRIC TRIANGLE (Fig. 1)
This triangle of the neck, bounded by the edge of the mandible and the anterior and posterior bellies of the digastric muscle, must be entered for excision of the submaxillary salivary gland or lymph nodes about it, for exposure of the mandible, and as part of a radical neck dissection or suprahyoid dissection. As the area is approached, usually through a transverse submandibular incision, one must look for the mandibular branch of the facial nerve. This tiny filament courses horizontally beneath the platysma and upon or in the underlying fascial layer, a varying distance of 0.5 to 2 cm. below the mandible. The nerve crosses superficial to the facial artery and accompanying anterior facial vein below the point where they cross the notch of the mandible. A bit posterior to this, a cervical branch of the nerve may be seen extending downward in the neck before the nerve itself disappears upward into the parotid. Anteriorly, before reaching the insertion of the digastric, the nerve curves upward over the edge of the mandible. This nerve is frequently difficult to identify. A helpful maneuver is to observe the corner of the mouth while sweeping the
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handle of the scalpel from the midpoint of the mandible downward on the neck. The lip will twitch as the nerve is crossed. Injury to this nerve results in paralysis of the lower lip on the involved side; fortunately in many instances there will be recovery, through anastomosing branches of the facial nerve. After the mandibular branch has been identified, and by dissection beneath it gently swept up to safety over the mandible, the superior border of the digastric triangle may be defined. A transverse incision is made on the lower free edge of the mandible commencing just back of the insertion of the anterior belly of the digastric. As the incision is carried down to bone, the contents of the triangle are bluntly pushed downward. Near the midpoint of the mandible, the facial artery and anterior facial vein must be divided. After freeing the superior border of the triangle, the anterior belly of the digastric is next exposed by sharp dissection. The submaxillary
Figure 1. The digastric triangle.
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salivary gland frequently bulges out of the triangle over the anterior belly of the digastric, but it is easily elevated as the muscle is followed downward from the mandible to its tendinous portion on the hyoid bone. The key to successful dissection from this point on is identification of the free posterior edge of the mylohyoid muscle. Failure to locate and retract this anatomical landmark leads to troublesome bleeding and possible injury to important structures. Dissection is commenced anteriorly in the acute angle formed by the mandible and the anterior belly of the digastric. Areolar tissues and one annoying small artery are divided as the mylohyoid is exposed. Dissection is then carried out directly upon the muscle, sweeping areolar tissue, lymph nodes, and an overhanging portion of the submaxillary gland posteriorly. At length a vertical free edge of the muscle is reached and success is at hand. A small retractor is used to retract the mylohyoid forward, exposing the floor of the digastric triangle formed by the hyoglossus. The submaxillary gland is pulled downward; this brings the large lingual nerve into view since it is attached to the gland by small nerve twigs (submaxillary ganglion). When this attachment is divided the lingual nerve again ascends behind the mandible. The submaxillary gland may now be rotated downward and Wharton's duct is identified, extending anteriorly and upward toward the floor of the mouth. The hypoglossal nerve becomes visible coursing obliquely upward and anteriorly upon the hypoglossus muscle. A fairly large lingual vein lies on either side of the hypoglossal nerve and bleeding is avoided by bluntly sweeping the submaxillary gland away from the floor of the triangle. The contents of the digastric triangle are now pulled posteriorly to complete the dissection as attention is directed to the posterior belly of the digastric. As this muscle is exposed the last remaining important structure is visualized. The facial artery which had been divided above at the mandible, enters the triangle posteriorly and inferiorly as it ascends beneath the posterior belly of the digastric to course along the deep surface of the submaxillary gland. It is a fairly large vessel as it enters the triangle just a short distance from its origin from the external carotid, and it must be carefully secured. Once the artery has been divided, dissection of the digastric triangle can be rapidly completed.
THE STERNOMASTOID OR CAROTID REGION (Fig. 2)
The broad sternocleidomastoid muscle covers a large portion of the lateral cervical region. Beneath it lie the carotid sheath and numerous important structures. A wide variety of surgical conditions require exposure of all or part of this area. These include branchial cleft cysts and sinuses, the important deep jugular lymph nodes, lesions of the carotid artery, neurogenic tumors, deep abscesses and pharyngeal diverticula. This zone
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must also be traversed for exposure of the anterior surface of the cervical spine. The key to successful dissection in this region is wide exposure and then retraction of the anterior margin of the sternocleidomastoid muscle. The outline of the muscle is easily noted by inspection and palpation of the neck. After the platysma and investing fascial layers are incised, the anterior margin of the muscle is isolated for as great a distance as the incision will allow and is then retracted posteriorly. As the fascia over the muscle is incised in the upper third of the neck, care must be taken to avoid injury to the great auricular nerve. This nerve, originating from 0-2 and 0-3, passes around the posterior border of the sternocleidomastoid"f1an d
Figure 2.
The sternomastoid or carotid region.
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curves forward and upward toward the ear, lying close to the anterior margin of the muscle. Injury to the nerve results in an annoying anesthesia of the lobe and posterior surface of the ear. The upper portion of the external jugular vein after its exit from the parotid lies close to the great auricular nerve. As the upper third of the sternomastoid is retracted the carotid sheath comes into view. This fascial layer is gently spread to expose the internal jugular vein which passes upward to disappear beneath the posterior belly of the digastric muscle. An important group of lymph nodes, the deep jugular nodes, lie along the course of the vein. A node or group of nodes lying upon the vein just inferior to the posterior belly of the digastric (subdigastric nodes) are among the first to be involved by metastatic cancer from the tongue, tonsil or pharynx. Further exposure in the upper carotid region requires identification and division of the common facial vein, a large tributary of the internal jugular. This vein extends anteriorly and upward from its junction with the jugular toward the submandibular region where it is formed by the confluence of the anterior and posterior facial veins. Just before its union with the jugular, the common facial may be joined by the superior thyroid and lingual veins. When the common facial vein is divided, the internal jugular may be retracted posteriorly for identification of deeper structures. The common carotid artery is located deep to the internal jugular vein. As the carotid is exposed, the vagus nerve must be identified; it lies on the surface of the carotid and accompanies the internal carotid above the bifurcation. The bifurcation of the artery is somewhat variable in position but generally lies opposite the superior margin of the thyroid cartilage. The superior thyroid artery is readily identified arising anteriorly from the external carotid near the origin of that vessel. The superior thyroid may originate so close to the carotid bifurcation that ligation of the external carotid artery requires preliminary ligation and division of the superior thyroid. A short distance above the carotid bifurcation the hypoglossal nerve must be identified for safe dissection in this region. This nerve descends from the skull between the internal jugular vein and internal carotid artery. As it emerges beneath the posterior belly of the digastric muscle, the nerve curves forward crossing the external carotid, giving off the descendens hypoglossi as it does so. The hypoglossal nerve is most easily identified at the point where it crosses the external carotid to course anteriorly and again dip beneath the digastric to enter the digastric triangle. It must be gently elevated for wide exposure of the external carotid. Two important structures lie deep to the carotid bifurcation, one a bit posteriorly and the other extending anteriorly. The posterior deep aspect of the artery is in close relation to the cervical sympathetic chain which lies upon the prevertebral fascia. The superior cervical ganglion may
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be identified as a bulbous swelling of the chain a short distance above the carotid bifurcation. Injury to the chain results in Horner's syndrome and unilateral absence of sweating of the face. Extending anteriorly beneath the carotid bifurcation is the superior laryngeal branch of the vagus nerve. This nerve leaves the vagus at the nodose ganglion located just below the jugular foramen. It passes deep to the carotid and curves forward beneath the superior thyroid artery, dividing into two branches to supply the larynx. Injury to this nerve results in partial anesthesia of the larynx, often with aspiration of food and saliva. One other structure must occasionally be identified in the upper carotid region. This is the spinal accessory nerve which upon leaving the jugular foramen crosses the internal jugular vein obliquely to extend downward and posteriorly in the neck. The nerve is usually obscured in areolar tissue close to the deep posterior surface of the sternocleidomastoid and it gives off a branch to the muscle, about 4 cm. below the mastoid process. It then enters the posterior cervical triangle which it traverses to reach the trapezius. The accessory nerve may be injured in the upper carotid region during excision of a branchial cleft cyst. Such cysts typically lie upon the carotid sheath beneath the upper third of the sternocleidomastoid. The deep posterior surface of the cyst is in close proximity to the accessory nerve. The lower carotid region has less complex anatomical relations. Exposure is again obtained by identifying and retracting the anterior margin of the sternocleidomastoid muscle. As this is accomplished the omohyoid muscle immediately comes into view as it crosses the carotid sheath obliquely behind the sternomastoid to ascend vertically with the prethyroid muscles. The omohyoid must be divided for adequate exposure. Division should be accomplished with care since the deep surface of the omohyoid lies immediately upon the internal jugular vein. Further exposure is afforded by division of the middle thyroid vein which courses transversely from the thyroid gland to the internal jugular. Once this is accomplished the carotid sheath may be retracted laterally and the larynx retracted medially for ready exposure of the prevertebral fascia, the bodies of the cervical vertebrae, and the esophagus. Only one additional structure, the inferior thyroid artery, crosses this plane rather low in the neck. This vessel emerges beneath the carotid sheath to reach the posterior aspect of the thyroid gland. It must usually be divided for adequate exposure and delivery of a pharyngoesophageal diverticulum. When the artery is divided, the larynx may be rotated to better expose the posterior surface of the thyroid and the esophagus. The recurrent laryngeal nerve can usually be identified entering the larynx just behind the cricothyroid articulation. Blunt dissection can be carried freely upward in the plane between the esophagus and the cervical vertebrae as high as the nasopharynx.
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THE SUPRACLAVICULAR REGION AND POSTERIOR TRIANGLE (Fig. 3)
This large compartment of the neck is bound by the middle third of the clavicle, the trapezius, and the posterior margin of the sternocleidomastoid. The prevertebral fascia covering the scalene muscles forms the floor of the triangle; there is direct communication with the mediastinum inferiorly and the axilla laterally. The space must be entered for lesions of the brachial plexus and subclavian artery, for removal of cervical ribs, for lymph node biopsy, and as part of a bloc dissection of the neck. In approaching this region the only important superficial structure to be encountered is the external jugular vein. This vessel courses beneath the platysma from the midportion of the sternocleidomastoid vertically toward the clavicle where it dips inward to join the subclavian vein. After the external jugular is divided and the investing layer of deep fascia incised the omohyoid muscle is seen to form a prominent landmark. It extends from the posterior corner of the triangle obliquely upward a variable distance above the clavicle to pass beneath the sternocleidomastoid and over the carotid sheath. The point at which the omohyoid emerges beneath the clavicle and the lower border of the trapezius forms the lower posterior boundary of a radical neck dissection. The omohyoid is enveloped by the pretracheal fascia which then extends inferiorly behind the clavicle to enclose the subclavian vein. When this fascial layer is incised one enters a plane in direct communication with the mediastinum and must identify a number of vital structures. The carotid sheath lies most medially in the supraclavicular region beneath the clavicular head of the sternocleidomastoid, which must be retracted or divided for adequate exposure. The junction of the internal jugular and subclavian veins is usually beneath the clavicle; occasionally, however, the subclavian vein may rise above the clavicle when the neck is extended. Immediately lateral to the jugular vein is the thoracic duct on the left and the right lymphatic duct on the right. These thin-walled lymphatic vessels ascend into the neck from the mediastinum, passing upward behind the carotid artery and jugular vein, and then arch downward to the lateral aspect of each jugular-subclavian junction. A vertically ascending jugular trunk may be seen joining each major lymph vessel and occasionally a subclavian trunk can be seen extending laterally. While ligation of the thoracic duct or right lymphatic duct may be performed with safety, undetected injury to either of these structures is followed by profuse lymph drainage which frequently requires operative treatment. Lateral to the carotid sheath and major lymphatic ducts is an important group of inferior deep cervical lymph nodes (scalene nodes) which lie grouped in loose areolar and fatty tissue. These nodes communicate with the deep jugular nodes above and serve as drainage areas for the mediastinum and infraclavicular viscera as well. Coursing transversely in this same region are transverse cervical and suprascapular arteries and veins.
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SURGICAL ANATOMY OF THE NECK
These vessels may be the source of troublesome bleeding during radical neck dissection or scalene lymph node biopsy. The arteries originate from the thyrocervical trunk of the subclavian artery or may arise independently from,the subclavian. They emerge on the medial edge of the scalenus anticus muscle and curve laterally to cross the lower neck, roughly parallel to the clavicle. Excessive traction on these vessels may avulse them from their subclavian origin. The scalenus anticus muscle lies beneath the scalene lymph nodes and extends between the subclavian vein and artery to insert on the first rib. The phrenic nerve is easily identified on the surface of the scalenus anticus; it is the only structure that passes in a medial direction as it descends in the neck. The subclavian artery beneath the scalenus anticus may take a
Trans. cervical a.
Figure 3.
Thyrocervical a.
The supraclavicular region and posterior triangle.
HARVEY
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W.
BAKER
surprisingly high curve up into the cervical region before dipping behind the clavicle laterally. As dissection is carried lateral to the scalene lymph nodes, the brachial plexus may be exposed beneath loose areolar and fatty tissue and beneath the transverse cervical and suprascapular vessels. The trunks of the brachial plexus emerge between the scalenus anticus and medius muscles and course obliquely downward and laterally to pass beneath the clavicle. Both the brachial plexus and subclavian artery may be elevated by a cervical rib; the artery may be compressed by the overlying scalenus anticus in this situation.
SUMMARY Important structures which may be encountered in many of the common surgical procedures in the neck have been described. Safe surgery in this region depends on a detailed knowledge of the anatomy, wide exposure, and careful hemostasis. 2250 N.W. Flanders Street Portland, Oregon 97210