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Anatomy of the Neck and Cervicothoracic Junction
Thorac Surg Clin 17 (2007) 529–547
Anatomy of the Neck and Cervicothoracic Junction Jean Deslauriers, MD, FRCS(C) Centre de Pneumologie de Laval, Department of Thoracic Surgery, 2725, Chemin Sainte-Foy, Que´bec, QC G1V 4G5, Canada
Although thoracic surgeons often use cervical and cervicothoracic incisions for operations on the upper airway, cervical esophagus, superior mediastinum, and lung apices, the neck and thoracic inlet are anatomically complex regions that traditionally have posed a problem for surgical access [1]. Important neurovascular structures traversing the neck often are crowded together, making exposure difficult and resectional surgery hazardous. Malignancies arising in the thoracic inlet such as anteriorly located Pancoast tumors or mediastinal neoplasms also may magnify the problem because they distort the normal anatomy in addition to invading local structures such as the spine, major blood vessels, or brachial plexus. The anatomic information that every thoracic surgeon must know and understand about the neck and thoracic inlet may not appear as such in standard anatomy textbooks, because in those volumes the anatomy is seen through the eyes of an anatomist rather those of a surgeon. Indeed there often are considerable differences in what is seen in an immobile cadaver lying in its back and what is observed in the operating room with patients lying in different positions. Attempts to perform operative procedures in the neck or over the cervicothoracic junction without both perspectives can result in incomplete operations or technical mishaps.
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Surgical landmarks and triangles of the neck Over the anterior neck, the laryngeal prominence (Adam’s apple) is formed by the angle of union of the two lateral laminae of the thyroid cartilage at the level of C4–C5 (Fig. 1). It is more prominent in men than in women because in men this angle of union is more acute. Above the laryngeal prominence, the laminae diverge to create a V-shaped depression, the thyroid notch. The anterior arch of the cricoid cartilage (level of C6) lies immediately inferior to the thyroid cartilage to which it is united by a thick and avascular membrane, the cricothyroid membrane. It is through this membrane that cricothyroidotomies [2] and minitracheotomies used for pulmonary toilet are performed [3,4]. Although upper tracheal rings sometimes can be felt at the base of the neck, they usually are not palpable because they are covered by the thyroid isthmus, which often must be divided or retracted superiorly to gain access to the upper trachea during an open tracheotomy or a tracheal resection. The hyoid bone (level of C3), which is not a true part of the larynx, lies above the thyroid cartilage, to which it is united by the thyrohyoid membrane. The thoracic inlet, which is the anatomic region where the neck communicates with the mediastinum, is the superior aperture (inlet) of the thorax. It is bounded by the spine posteriorly (level of T1), the cartilage of the first ribs laterally, and the sternal (jugular) notch anteriorly. The sternocleidomastoid muscle, which runs superiorly and laterally from the manubrium (sternal head) and the medial half of the clavicle (clavicular head) to the mastoid process of the temporal bone (Fig. 2), divides the side of the
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DESLAURIERS
Body of hyoid bone Thyrohyoid membrane
Thyroid notch Thyroid cartilage Laryngeal prominence
Cricothyroid membrane
Anterior cricoid arch First tracheal ring
Thyroid
Fig. 1. The laryngeal landmarks of the anterior neck. Note the two laminae of the thyroid cartilage that are fused together in the midline to form the laryngeal prominence.
neck into anterior and posterior triangles, which are important descriptive landmarks (Box 1). The supraclavicular fossa is a depression located above the clavicle lateral to the clavicular site of insertion of the sternocleidomastoid muscle. Muscles and skeleton of the neck In the neck, there are several groups of muscles, all of which are important to the thoracic
surgeon. These muscles include the prevertebral muscles, the scalene muscles, the infrahyoid and suprahyoid muscles, the sternocleidomastoid muscle, the platysma, and, over the back of the neck, the trapezius muscle. There are three sets of deep prevertebral muscles which are covered by the prevertebral fascia and whose actions are to flex the neck and to flex the head on the neck. The scalene muscles (Box 2) have an oblique orientation from their origin on the transverse
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Sternocleidomastoid muscle
Mandible Posterior triangle
Anterior triangle
Clavicle Inferior belly of omohyoid muscle
Supraclavicular triangle Fig. 2. Topography of the triangles of the neck. Note that the inferior belly of the omohyoid muscle divides the posterior triangle into an occipital triangle and a supraclavicular triangle.
processes of the cervical vertebrae to their sites of insertion on the superior border of the first two ribs (Figs. 3 and 4). The scalene anterior is located under the sternocleidomastoid muscle and inserts on the scalene tubercle of the first rib. The subclavian vein passes in front of it to unite with the internal jugular vein; the subclavian artery, and brachial plexus pass behind it. The scalenus medius also inserts on the superior border of the first rib lateral to the scalenus anterior, and the scalenus posterior muscle inserts on the external surface of the second rib. The scalene
triangle is bounded by the scalenus anterior anteriorly, the scalenus medius posteriorly, and the first rib inferiorly. Collectively, the scalene muscles elevate the first two ribs and thus are considered inspiratory muscles. For the thoracic surgeon, the importance of the costoclavicular space and of the scalene triangle is that anatomic variations can cause compression of the brachial plexus and subclavian artery (see the article on the anatomy of the thoracic outlet by Urschel in this issue). When a Pancoast tumor is resected from the anterior cervical approach, the middle
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DESLAURIERS
Box 1. Boundaries of the triangles of the neck Anterior triangle Anterior border of sternocleidomastoid muscle Inferior margin of mandible Anterior midline of the neck Posterior triangle Posterior border of sternocleidomastoid muscle Middle part of clavicle Anterior border of trapezius
Box 2. Origin and site of insertion of the scalene muscles Scalenus anterior Origin: Transverse process of C3–C6 Insertion: Scalene tubercle on the superior border of the first rib Scalenus medius Origin: Transverse process of C2–C7 Insertion: Superior border of first rib, lateral to the scalenus anterior Scalenus posterior Origin: Transverse process of C4–C6 Insertion: Superior border of second rib
and anterior scalenus muscles must be divided above their site of insertion on the first rib to gain access to the brachial plexus. The infrahyoid muscles (Box 3) lie inferior to the hyoid bone and are called ‘‘strap muscles’’ because they have a ribbon-like appearance. They anchor the hyoid bone to the sternum, clavicle, and scapula. These muscles include the sternothyroid, the thyrohyoid, the sternohyoid, and the omohyoid, which has two bellies (anterior and posterior) united by an intermediate tendon (Fig. 5) and extends obliquely from the hyoid bone to the scapula. Between the leftand right-sided strap muscles, a layer of loose connective tissue must be accessed and elevated to gain access to the prevertebral fascia and
superior mediastinum while doing a mediastinoscopy. As a group, the infrahyoid muscles depress the hyoid bone and larynx and thus help lower the lower jaw during the process of swallowing. The suprahyoid muscles (Box 4) are located in the submandibular region superior to the hyoid bone and connect the hyoid bone to the skull (see Fig. 5). These muscles include the geniohyoid (deep layer), the mylohyoid (middle layer), and the stylohyoid muscles (superficial layer). The digastric muscle also is superficial and, like the omohyoid, has an anterior and a posterior belly united by an intervening tendon. The posterior belly arises from the mastoid process (temporal bone), and the anterior belly is attached on the digastric fossa on the inferior border of the mandible. Collectively, the suprahyoid muscles lower the lower mandible (geniohyoid, mylohyoid, anterior belly of digastric) or elevate the hyoid bone (posterior belly of digastric, stylohyoid). The sternocleidomastoid muscle (Fig. 6) is a large muscle located in the anterolateral portion of the neck. As previously described, it extends obliquely up the neck from the manubrium (sternal head) and medial third of the clavicle (clavicular head) to the mastoid process of the temporal bone. Its main actions are to flex the head and tilt the head. It is crossed superficially by the external jugular vein, and it covers the great vessels of the neck. The platysma muscle is a wide, thin quadrilateral muscle that covers the front and side of the neck and the lower face. The important muscle in the posterior part of the neck is the trapezius (Fig. 7), which is a wide, thin, and triangular muscle extending from the spinous processes of C7 and T1 to T10 to the clavicle (posterior lateral third), the acromion, and the scapula. Its action is to elevate and rotate the scapula. The bony skeleton of the neck consists of the upper sternum, clavicles, first ribs, and cervical vertebrae. The upper sternum is called the ‘‘manubrium’’; its superior surface is indented by a depression, suprasternal or jugular notch. On each side of this notch is the articular facet for the articulation of the medial end of the clavicle (see Fig. 4). Part of the sternodeidomastoid muscles originates from the anterior surface of the manubrium. The clavicle or collarbone extends from the manubrium (sternoclavicular joint) to the
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C2 Scalenus anterior muscle
C3
Scalenus medius muscle
C4
C5 Scalenus posterior muscle
C6
C7
Scalene tubercle
First rib
Second rib
Fig. 3. The origin and insertion of the scalene muscles. Note that the anterior scalenus and middle scalenus insert on the first rib, whereas the posterior scalenus inserts on the second rib.
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DESLAURIERS
C1
C2
Origins of Scalenus medius muscle
C3
C4 C5
Insertion of Scalenus medius muscle
Origins of Scalenus anterior muscle
C6 C7
Scalenus anterior muscle Scalenus medius muscle Scalenus posterior muscle
Insertion of Scalenus anterior muscle
First rib
Clavicle Second rib
Fig. 4. Topographic anatomy of the scalene muscles. The scalene muscles descend obliquely from the transverse processes of the cervical vertebrae to the first two ribs.
acromion of the scapula laterally (acromioclavicular joint). This latter articulation connects the upper limb to the chest wall. The clavicle is important for the stability of the shoulder–girdle complex. The acromioclavicular joint, whose construction is reinforced by the powerful coracoclavicular ligament, provides mobility between clavicle and scapula [5]. In their original description of the anterior transcervical–thoracic approach for the resection
of Pancoast tumors, Dartevelle and colleagues [6] recommended that the medial half of the clavicle be resected to gain better surgical exposure. Because the clavicle is the site of insertion of the sternocleidomastoid muscle (superior surface) and of the pectoralis major muscle (inferior surface), and because it stabilizes the shoulder girdle, its resection can lead to shoulder instability, especially when the clavicular resection is associated with first rib resection and cervical
ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Box 3. Infrahyoid muscles (strap muscles) Superficial plane Sternothyroid Extends from sternum to thyroid cartilage Located deep to sternohyoid muscle Omohyoid Extends from the hyoid bone to the scapula Has two bellies united by a tendon Deep plane Thyrohyoid Continuation of sternothyroid muscle up to the hyoid bone Sternohyoid Anterior to sternothyroid and thyrohyoid Extends from clavicle to hyoid bone
vertebra resection. Because clavicular resection also can lead to serious alterations of shoulder mobility, cervical posture, and discomfort, most thoracic surgeons now advocate the transmanubrial approach described by Grunenwald and Spaggiari [7]. This approach spares the clavicle and all its muscular insertions while affording excellent access to the supraclavicular region. The first rib is important for maintaining stability of the shoulder girdle. It is the shortest, broadest, and most curved of all ribs, and it extends from the lateral margin of the manubrium inferior to the clavicular notch to a single-facet articulation with the body of the first thoracic vertebra. The first rib has a prominent scalene tubercle on the inner border of its superior surface for the insertion of the scalene anterior muscle. This site of insertion is important because the scalene triangle located between the scalene anterior muscle anteriorly, the scalene medius muscle posteriorly, and the first rib inferiorly allows the passage of the subclavian artery and brachial plexus. The subclavian vein crosses the first rib in front of the scalene tubercle and scalene anterior muscle. The cervical spine is made of seven vertebrae (C1–C7), the first one being called the ‘‘atlas,’’ the second one the ‘‘axis,’’ and the seventh the ‘‘vertebra prominens’’ because of its long spinous process that can be palpated easily and seen
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through the skin. Their distinctive feature is their transverse process, which circumscribes the transverse foramen through which the vertebral arteries and veins pass. The sixth cervical vertebra has a prominent anterior tubercle of its transverse process called the ‘‘tubercle de Chassignac,’’ which has a close relationship with the common carotid artery.
Topographic anatomy of the neck: anterior and posterior triangles Topographically, the neck is divided into an anterior and a posterior triangle by the sternocleidomastoid muscle (see Box 1 and Fig. 2). Complete knowledge of the anatomy of these triangles is important for the thoracic surgeon operating in the area, because they contain many important structures that must be identified and preserved during surgery. Superior sulcus tumors located anteriorly and extending in front of the anterior scalene muscle, for example, may invade the subclavian and internal jugular veins, whereas tumors extending between the anterior and medius scalene muscles may invade the phrenic nerve, the subclavian artery and its branches, and the brachial plexus [8]. The general shape of the posterior triangle of the neck is that of a triangle whose base is the middle third of the clavicle and whose apex is the meeting of the sternocleidomastoid muscle and trapezius muscles on the superior nuchal line. Its exact boundaries are presented in Box 1. The floor of the posterior triangle is made of four muscles, including the scalenus medius and scalenus posterior, which are covered by a deep cervical fascia. The inferior belly of the omohyoid muscle divides the posterior triangle into an occipital triangle (superior to the omohyoid) and a supraclavicular triangle that is crossed superficially by the external jugular vein. The anterior triangle of the neck, whose apex is the sternal notch and whose base is the inferior border of the mandible, contains the common carotid artery and its division into external and internal branches (carotid triangle).
Topographic anatomy of the neck: the root of the neck The root of the neck, the thoracocervical region, is bounded laterally by the first ribs, anteriorly by the sternal notch and manubrium,
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DESLAURIERS
Anterior belly of digastric muscle
Mylohyoid muscle
Stylohyoid muscle Thyrohyoid muscle
Posterior belly of digastric muscle
Sternocleidomastoid muscle (cut) Sternohyoid muscle
Sternothyroid muscle
Anterior belly of omohyoid muscle Posterior belly of omohyoid muscle
Fig. 5. Topography of the infrahyoid and suprahyoid muscles. Note the two bellies of the omohyoid muscle united by an intermediate tendon.
and posteriorly by the first dorsal vertebra (D1). Its general arrangement is shown diagrammatically in Fig. 8. Veins and thoracic duct When Pancoast tumors are resected through the anterior cervical approach, the venous system
(Fig. 9) at the root of the neck (Box 5) is usually dissected first. Most of the external jugular vein is located in the posterior triangle of the neck, where it runs downward crossing the sternocleidomastoid muscle obliquely to empty into the subclavian vein. The anterior jugular vein’s anatomy is variable as it arises from submental venous plexuses and
ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Box 4. Suprahyoid muscles (connect the hyoid bone to the skull) Deep layer Geniohyoid: Extends from inferior maxillary to the hyoid bone Middle layer Mylohyoid Large and thin muscle that supports the floor of the mouth Located above the anterior belly of digastric muscle Superficial layer Stylohyoid: Small strip of muscle located along the upper border of posterior belly of digastric Digastric Has two bellies (anterior, posterior) joined by an intervening tendon Anterior belly arises from mandible Posterior belly arises from mastoid process
drains into the external jugular vein posterior to the sternocleidomastoid muscle. The subclavian vein begins on the lateral border of the first rib and crosses that rib anterior to the scalenus anterior muscle (anterior to scalene tubercle). On the medial border of the scalenus anterior muscle it joins the internal jugular vein to form the innominate vein. The internal jugular vein is the largest vein of the neck. It begins in the posterior cranial fossa, where it drains blood from the brain, and runs inferiorly lateral to the carotid artery (carotid sheath) in the anterior triangle of the neck. It then passes deep to the sternocleidomastoid muscle to unite with the subclavian vein to form the innominate vein posterior to the sternal end of the clavicle. On the left side, the thoracic duct, which ascends from the mediastinum, empties in the venous system at the union of the left internal jugular vein and subclavian vein. When Pancoast tumors are resected through the cervicothoracic approach, all branches of the subclavian vein must be visualized clearly, and proximal and distal control should be obtained early during the dissection. If the subclavian vein
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is invaded by the tumor, it can be resected without a need for reconstruction. On the left side, ligation of the thoracic duct usually is required. Arteries of the root of the neck The right subclavian artery (Box 6) is a terminal branch of the innominate artery. The left subclavian artery originates directly from the aortic arch. Both arteries enter the root of the neck behind their respective sternoclavicular joints. Each artery then arches superiorly and posteriorly behind the scalenus anterior muscle. Three branches of the subclavian artery originate in the sternocleidomastoid region. The first and most important one is the vertebral artery, which arises in the first portion of the artery medial to the anterior scalenus muscle. Next to the vertebral branch and also medial to the scalene anterior muscle is the thyrocervical trunk, which gives rise to the inferior thyroid artery and to the ascending cervical branch that supplies the muscles of the posterior triangle of the neck. The internal mammary branch arises from the inferior aspect of the subclavian artery opposite the thyrocervical trunk. It runs downward into the thorax parallel to the sternum. During surgery for Pancoast tumors, the subclavian artery and its branches must be dissected. This maneuver is much easier when the operation is done from above, through the anterior supraclavicular approach. If necessary, the subclavian artery can be resected locally and reconstruction performed either with an end-to-end anastomosis or graft interposition. The vertebral artery never should be sacrificed unless the continuity of the circle of Willis has been well documented preoperatively. Nerves of the root of the neck From the skull, the vagus nerve passes inferiorly through the neck within the carotid sheath behind the internal carotid artery and internal jugular vein. At the base of the neck, the right vagus nerve crosses the origin of the right subclavian artery behind the sternoclavicular joint, where it gives off the right recurrent laryngeal nerve (inferior laryngeal nerve) that loops around and under the subclavian artery (Figs. 10 and 11). This nerve ascends in the tracheoesophageal groove (Box 7), where it can be injured during extensive cervicomediastinal dissections done for tumors located near or at the
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DESLAURIERS
Posterior belly of digastric muscle
Anterior belly of digastric muscle
Posterior scalene muscle
Anterior belly of omohyoid muscle
Middle scalene muscle
Sternocleidomastoid muscle
Posterior belly of omohyoid muscle Anterior scalene muscle
Fig. 6. Lateral view of the neck muscles showing the sternocleidomastoid muscle.
thoracic inlet. On the left side, the recurrent laryngeal nerve originates close to the ligamentum arteriosum where it courses around the aortic arch from front to back before ascending to the neck, also in the tracheoesophageal groove. On each side, the recurrent nerves accompany the laryngeal branch of the inferior thyroid artery deep to the inferior constrictor muscle of the pharynx behind the cricothyroid articulation. Before entering the larynx, each recurrent nerve sends off 8 to 14 short branches into the lateral wall of the esophagus; these branches sometimes can be
seen when operating on the upper esophageal sphincter. The recurrent nerves supply all of the intrinsic muscles of the larynx except the cricothyroid muscle. In general, the right recurrent nerve has a more asymmetrical and diagonal course than the left recurrent nerve, and this course is one of the reasons most surgeons choose the left thoracic inlet as the venue for transposing colon or stomach [9,10]. The superior laryngeal nerves arise from the vagus nerves in the neck behind the upper portion
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ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Sternocleidomastoid muscle
Rhomboideus minor muscle
Trapezius muscle
Rhomboideus major muscle
Latissimus dorsi muscle
Fig. 7. Topography of the trapezius muscle.
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DESLAURIERS
C5
Scalenus anterior muscle
C6 Phrenic nerve
C7 C8
T1 Superior trunk of brachial plexus Clavicle
Middle trunk of brachial plexus Lower trunk of brachial plexus
Cords of brachial plexus
First rib
Subclavian artery
Subclavian vein
Fig. 8. General anatomy of the cervicothoracic region (the root of the neck).
of the triangle made by the carotid artery bifurcation and almost immediately divide into two terminal branches. The internal laryngeal nerve pierces the thyrohyoid membrane with the superior laryngeal artery; the external branch accompanies the superior thyroid artery posterior to the sternothyroid muscle. The phrenic nerve arises from C3-to-C5 (the main root arises from C4) and descends obliquely in the neck on the anterior surface of the scalenus anterior muscle. At the base of the neck, it is
located over the medial surface of this muscle, 3 to 4 cm lateral to the sternoclavicular joint. The phrenic nerve descends posterior to the subclavian vein and anterior to the internal mammary artery to enter the thorax. Surgically, the phrenic nerve can be accessed by a transverse incision made over the posterior border of the sternocleidomastoid muscle 2 fingerbreadths above the clavicle. With the sternocleidomastoid muscle and internal jugular vein retracted medially, the phrenic nerve can be seen
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Scalenus medius muscle
Scalenus anterior muscle Facial vein
External jugular vein
Sternocleidomastoid muscle
Internal jugular vein
Anterior jugular vein Omohyoid muscle (inferior belly)
Subclavian vein Innominate vein Fig. 9. Veins at the root of the neck.
over the anterior surface of the scalene anterior muscle. It can be injured during a prescalene nodal biopsy for the purpose of staging lung cancer [11,12], because the floor of the prescalene space is formed by the scalenus anterior muscle with the phrenic nerve lying in its sheath. During resection of a Pancoast tumor through the cervicothoracic approach, every attempt should be made to preserve the phrenic nerve; for this reason the scalene anterior muscle must be divided as close to its site of insertion on the first rib as possible. The cervical sympathetic trunks (see Fig. 10) are made of three sympathetic ganglia (Box 8) joined by intermediate longitudinal strands of nerve fibers. There structures are located on the
prevertebral fascia, which separates them from the transverse processes of the cervical vertebrae. The superior ganglion is large and fusiform and is located at the level of the second and third cervical vertebrae. The middle cervical ganglion is small and inconsistent and is located at the level of the sixth cervical vertebra. The inferior cervical ganglion or stellate ganglion lies anterior to the transverse process of C7 near the superior border of the neck of the first rib. The stellate ganglion also is known as the ‘‘cervicothoracic ganglion’’ because it is generally fused with the first thoracic ganglion. Although it is called the ‘‘stellate ganglion,’’ its form can be quite variable (eg, semilunar or circular), and indeed it is seldom starshaped.
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DESLAURIERS
Box 5. Veins at the root of the neck
Box 6. Arteries at the root of the neck
External jugular vein Drains mandibular and auricular regions Located in posterior triangle of the neck Empties into subclavian vein
Right subclavian artery Originates from the innominate artery Enters the root of the neck behind the sternoclavicular joint
Anterior jugular vein Drains submental regions Variable anatomy Empties into internal jugular vein
Left subclavian artery Originates from the aortic arch Ascends and enters the root of the neck behind the left sternoclavicular joint
Subclavian vein Continuation of axillary vein Crosses the first rib anterior to the scalene anterior muscle
Branches of the subclavian arteries Vertebral: Arises medial to the scalenus anterior muscle Thyrocervical trunk: Gives rise to inferior thyroid and ascending cervical branches Internal mammary: Arises from inferior aspect of subclavian artery Descends inferomedially into the thorax
Internal jugular vein Drains blood from the brain Runs inferiorly lateral to the common carotid artery Crosses deep to the sternocleidomastoid muscle to unite with the subclavian vein
Fascia and fascial spaces of the neck The fascial planes (Box 9) and spaces (Box 10) of the neck are important to the thoracic surgeon because they connect the mediastinum with the neck, and air (pneumomediastinum) or infection (mediastinitis) can travel that route. The fascia of the neck comprise three layers, the superficial or investing fascia, the middle or pretracheal fascia, and the posterior or prevertebral fascia. The superficial (investing) fascia is deep to the subcutaneous fascia and encircles the neck completely, investing the platysma, sternocleidomastoid, and trapezius muscles. Superiorly it is attached to the superior nuchal line and spinous processes of the cervical vertebrae, and inferiorly it is attached to the manubrium, clavicle, and scapula. Superior to the sternal notch, this fascia splits into two layers that are attached to the anterior and posterior manubrium. The space between these two layers, the suprasternal space or space of Burns, contains the sternal heads of the sternocleidomastoid muscles and the arch of the internal jugular vein. The middle or pretracheal fascia extends from the thyroid and cricoid cartilages down into the thorax. It is an extensive fascia that
splits to surround the thyroid gland, trachea, and esophagus completely. It invests the strap muscles, and laterally it fuses with the superficial fascia opposite the carotid sheath. In cases of spontaneous pneumomediastinum, interstitial air usually reaches the neck by dissecting along this fascia [13]. The posterior cervical fascia consists of two layers. The first or alar fascia lies posterior to the visceral compartment of the neck and continues laterally to form the carotid sheath. The second or prevertebral fascia extends from the base of the skull to the third thoracic vertebra and covers the prevertebral muscles. There are two cervicothoracic spaces (Fig. 12) of importance to the thoracic surgeon, the previsceral or pretracheal space and the retrovisceral or retropharyngeal space (see Box 10). The pretracheal space, which lies beneath the strap muscles, is opened during mediastinoscopy, thyroid surgery, and surgery of the cervical trachea. It extends from the thyroid cartilage above to the upper border of the aortic arch where it terminates by adhesions extending from the fibrous pericardium to the posterior surface of the manubrium. These fibrous adhesions form
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Superior cervical ganglion Vagus nerve (CN X) Sympathetic trunk
Middle cervical ganglion Common carotid artery Scalenus anterior muscle Cupula Phrenic nerve
Inferior cervical (Stellate) ganglion Vertebral artery
Subclavian artery
Ansa subclavia
Right recurrent laryngeal nerve
Fig. 10. Arteries and nerves at the root of the neck.
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DESLAURIERS
Superior laryngeal nerve
Left vagus nerve (CN X) Right vagus nerve (CN X) Trachea
Right recurrent laryngeal nerve
Left recurrent laryngeal nerve
Esophagus
Fig. 11. Anatomy of the left and right recurrent laryngeal nerves.
ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Box 7. Anatomy of the recurrent laryngeal nerves (inferior laryngeal nerves) Right recurrent laryngeal nerve Loops around the right subclavian artery Ascends in tracheoesophageal groove Has a more asymmetric and diagonal course than the left recurrent nerve Left recurrent laryngeal nerve Loops around the aortic arch near the ligamentum arteriosum Ascends in the tracheoesophageal groove
a relative barrier to the downward gravitational spread of infection. The retrovisceral or retropharyngeal space consists of loose connective tissue located in front of the prevertebral fascia. It extends from the skull through the neck and posterior mediastinum down to the diaphragm. Laterally, it seals off at the transverse processes of the cervicothoracic vertebrae. This space is of considerable importance, because retropharyngeal abscesses secondary to oropharyngeal infections can spread to the mediastinum producing a diffuse necrotizing mediastinitis [14,15].
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Box 9. Fascias of the neck Superficial (investing) fascia Encircles the neck completely Attached superiorly to superior nuchal line and spinous processes of C1–C7 Attached inferiorly to manubrium, clavicle, and scapula Middle (pretracheal) fascia Extends from thyroid and cricoid cartilages down into the thorax Splits to surround the thyroid, trachea, and esophagus completely Posterior (prevertebral) fascia Extends from the base of the skull to the third thoracic vertebra Covers prevertebral muscles
Box 10. Cervicothoracic fascial spaces Pretracheal (previsceral) space Located between trachea and strap muscles and between trachea and posterior manubrium Extends from thyroid cartilage to upper border of aortic arch (T4) Retropharyngeal (retrovisceral) space Located in front of the prevertebral fascia Extends from the skull to the diaphragm
Box 8. Sympathetic ganglia of the neck Superior cervical ganglion Large and fusiform Located at the level of C2, C3 Middle cervical ganglion Small and inconsistent Located at the level of C6 Inferior cervical ganglion (stellate ganglion) Generally fused with the first thoracic ganglion Located at the level of C7 Seldom star-shaped
Summary All thoracic surgeons must have an extensive knowledge of the anatomy of the neck, because cervical approaches are used on an almost daily basis to access the cervical trachea, upper esophagus, and superior mediastinum. In addition to basic and scholarly knowledge of anatomy, they also must understand the anatomic relationships among the neck, the mediastinum, and both pleural spaces. Indeed, such knowledge forms the basis for the diagnosis and management of many aspects of pulmonary, mediastinal, and esophageal pathologies.
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DESLAURIERS
Previsceral space
Retrovisceral space
Fig. 12. The anatomy of the previsceral and retrovisceral spaces.
ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Further readings Moore KL. Clinically oriented anatomy. 2nd edition. Baltimore (MD): Williams and Wilkins; 1985. Gardner E, Gray DJ, O’Rahilly R. Anatomy: a regional study of human structure. 3rd Edition. Philadelphia: WB Saunders Co; 1969.
References [1] Korst RJ, Burt ME. Cervicothoracic tumors: results of resection by the hemi-clamshell approach. J Thorac Cardiovasc Surg 1998;15:286–95. [2] Brantigan CO, Grow JB. Cricothyroidotomy: elective use in respiratory problems requiring tracheotomy. J Thorac Cardiovasc Surg 1976;71:72–81. [3] Matthews HR, Hopkinson RB. Treatment of sputum retention by minitracheotomy. Br J Surg 1984; 71:147–50. [4] Bonde P, Papachristos I, McCrath A, et al. Sputum retention after lung operation: prospective, randomized trial shows superiority of prophylactic minitracheotomy in high-risk patients. Ann Thorac Surg 2002;74:196–203. [5] Urschel HC, Lord JW. Surgery of the clavicle. In: Pearson FG, Cooper JD, Deslauriers J, et al, editors. Thoracic surgery. 2nd edition. Churchill Livingstone; 2002. p. 1490–8. [6] Dartevelle PG, Chapelier AR, Macchiarini P, et al. Anterior transcervical-thoracic approach for radical
[7]
[8] [9]
[10]
[11]
[12] [13]
[14]
[15]
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resection of lung tumors invading the thoracic outlet. J Thorac Cardiovasc Surg 1993;105:1025–34. Grunenwald D, Spaggiari L. Transmanubrial osteomuscular sparing approach for apical chest tumors. Ann Thorac Surg 1997;63:563–6. Dartevelle P, Macchiarini P. Surgical management of superior sulcus tumors. Oncologist 1999;4:398–407. Liebermann-Meffert DMI, Walbrun BW, Hiebert CA, et al. Recurrent and superior laryngeal nerves: a new look with implications for the esophageal surgeon. Ann Thorac Surg 1999;67:217–23. Hiebert CA, Liebermann-Meffert D, Kraus DH. Laryngeal nerve palsy. In: Pearson FG, Cooper JD, Deslauriers J, et al, editors. Thoracic surgery. 2nd edition. Churchill Livingstone; 2002. p. 331–40. Daniels AC. A method of biopsy useful in diagnosing certain intrathoracic diseases. Dis Chest 1949; 16:360–7. Connar RG. Prescalene and deep cervical lymph node biopsy. Surg Gynecol Obstet 1955;101:733–43. Kezler P. Surgical pathology of bullae with and without pneumothorax. Eur J Cardiothorac Surg 1988;2:416–24. Cogan MIC. Necrotizing mediastinitis secondary to descending cervical cellulitis. Oral Surg Oral Med Oral Pathol 1973;36:307. Estreka AS, Landay MV, Grisham JM, et al. Descending necrotizing the mediestinitis. Surg Gynecol Obstet 1983;157:545–52.
Anatomy of the Neck and Cervicothoracic Junction Jean Deslauriers, MD, FRCS(C) Centre de Pneumologie de Laval, Department of Thoracic Surgery, 2725, Chemin Sainte-Foy, Que´bec, QC G1V 4G5, Canada
Although thoracic surgeons often use cervical and cervicothoracic incisions for operations on the upper airway, cervical esophagus, superior mediastinum, and lung apices, the neck and thoracic inlet are anatomically complex regions that traditionally have posed a problem for surgical access [1]. Important neurovascular structures traversing the neck often are crowded together, making exposure difficult and resectional surgery hazardous. Malignancies arising in the thoracic inlet such as anteriorly located Pancoast tumors or mediastinal neoplasms also may magnify the problem because they distort the normal anatomy in addition to invading local structures such as the spine, major blood vessels, or brachial plexus. The anatomic information that every thoracic surgeon must know and understand about the neck and thoracic inlet may not appear as such in standard anatomy textbooks, because in those volumes the anatomy is seen through the eyes of an anatomist rather those of a surgeon. Indeed there often are considerable differences in what is seen in an immobile cadaver lying in its back and what is observed in the operating room with patients lying in different positions. Attempts to perform operative procedures in the neck or over the cervicothoracic junction without both perspectives can result in incomplete operations or technical mishaps.
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Surgical landmarks and triangles of the neck Over the anterior neck, the laryngeal prominence (Adam’s apple) is formed by the angle of union of the two lateral laminae of the thyroid cartilage at the level of C4–C5 (Fig. 1). It is more prominent in men than in women because in men this angle of union is more acute. Above the laryngeal prominence, the laminae diverge to create a V-shaped depression, the thyroid notch. The anterior arch of the cricoid cartilage (level of C6) lies immediately inferior to the thyroid cartilage to which it is united by a thick and avascular membrane, the cricothyroid membrane. It is through this membrane that cricothyroidotomies [2] and minitracheotomies used for pulmonary toilet are performed [3,4]. Although upper tracheal rings sometimes can be felt at the base of the neck, they usually are not palpable because they are covered by the thyroid isthmus, which often must be divided or retracted superiorly to gain access to the upper trachea during an open tracheotomy or a tracheal resection. The hyoid bone (level of C3), which is not a true part of the larynx, lies above the thyroid cartilage, to which it is united by the thyrohyoid membrane. The thoracic inlet, which is the anatomic region where the neck communicates with the mediastinum, is the superior aperture (inlet) of the thorax. It is bounded by the spine posteriorly (level of T1), the cartilage of the first ribs laterally, and the sternal (jugular) notch anteriorly. The sternocleidomastoid muscle, which runs superiorly and laterally from the manubrium (sternal head) and the medial half of the clavicle (clavicular head) to the mastoid process of the temporal bone (Fig. 2), divides the side of the
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DESLAURIERS
Body of hyoid bone Thyrohyoid membrane
Thyroid notch Thyroid cartilage Laryngeal prominence
Cricothyroid membrane
Anterior cricoid arch First tracheal ring
Thyroid
Fig. 1. The laryngeal landmarks of the anterior neck. Note the two laminae of the thyroid cartilage that are fused together in the midline to form the laryngeal prominence.
neck into anterior and posterior triangles, which are important descriptive landmarks (Box 1). The supraclavicular fossa is a depression located above the clavicle lateral to the clavicular site of insertion of the sternocleidomastoid muscle. Muscles and skeleton of the neck In the neck, there are several groups of muscles, all of which are important to the thoracic
surgeon. These muscles include the prevertebral muscles, the scalene muscles, the infrahyoid and suprahyoid muscles, the sternocleidomastoid muscle, the platysma, and, over the back of the neck, the trapezius muscle. There are three sets of deep prevertebral muscles which are covered by the prevertebral fascia and whose actions are to flex the neck and to flex the head on the neck. The scalene muscles (Box 2) have an oblique orientation from their origin on the transverse
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Sternocleidomastoid muscle
Mandible Posterior triangle
Anterior triangle
Clavicle Inferior belly of omohyoid muscle
Supraclavicular triangle Fig. 2. Topography of the triangles of the neck. Note that the inferior belly of the omohyoid muscle divides the posterior triangle into an occipital triangle and a supraclavicular triangle.
processes of the cervical vertebrae to their sites of insertion on the superior border of the first two ribs (Figs. 3 and 4). The scalene anterior is located under the sternocleidomastoid muscle and inserts on the scalene tubercle of the first rib. The subclavian vein passes in front of it to unite with the internal jugular vein; the subclavian artery, and brachial plexus pass behind it. The scalenus medius also inserts on the superior border of the first rib lateral to the scalenus anterior, and the scalenus posterior muscle inserts on the external surface of the second rib. The scalene
triangle is bounded by the scalenus anterior anteriorly, the scalenus medius posteriorly, and the first rib inferiorly. Collectively, the scalene muscles elevate the first two ribs and thus are considered inspiratory muscles. For the thoracic surgeon, the importance of the costoclavicular space and of the scalene triangle is that anatomic variations can cause compression of the brachial plexus and subclavian artery (see the article on the anatomy of the thoracic outlet by Urschel in this issue). When a Pancoast tumor is resected from the anterior cervical approach, the middle
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DESLAURIERS
Box 1. Boundaries of the triangles of the neck Anterior triangle Anterior border of sternocleidomastoid muscle Inferior margin of mandible Anterior midline of the neck Posterior triangle Posterior border of sternocleidomastoid muscle Middle part of clavicle Anterior border of trapezius
Box 2. Origin and site of insertion of the scalene muscles Scalenus anterior Origin: Transverse process of C3–C6 Insertion: Scalene tubercle on the superior border of the first rib Scalenus medius Origin: Transverse process of C2–C7 Insertion: Superior border of first rib, lateral to the scalenus anterior Scalenus posterior Origin: Transverse process of C4–C6 Insertion: Superior border of second rib
and anterior scalenus muscles must be divided above their site of insertion on the first rib to gain access to the brachial plexus. The infrahyoid muscles (Box 3) lie inferior to the hyoid bone and are called ‘‘strap muscles’’ because they have a ribbon-like appearance. They anchor the hyoid bone to the sternum, clavicle, and scapula. These muscles include the sternothyroid, the thyrohyoid, the sternohyoid, and the omohyoid, which has two bellies (anterior and posterior) united by an intermediate tendon (Fig. 5) and extends obliquely from the hyoid bone to the scapula. Between the leftand right-sided strap muscles, a layer of loose connective tissue must be accessed and elevated to gain access to the prevertebral fascia and
superior mediastinum while doing a mediastinoscopy. As a group, the infrahyoid muscles depress the hyoid bone and larynx and thus help lower the lower jaw during the process of swallowing. The suprahyoid muscles (Box 4) are located in the submandibular region superior to the hyoid bone and connect the hyoid bone to the skull (see Fig. 5). These muscles include the geniohyoid (deep layer), the mylohyoid (middle layer), and the stylohyoid muscles (superficial layer). The digastric muscle also is superficial and, like the omohyoid, has an anterior and a posterior belly united by an intervening tendon. The posterior belly arises from the mastoid process (temporal bone), and the anterior belly is attached on the digastric fossa on the inferior border of the mandible. Collectively, the suprahyoid muscles lower the lower mandible (geniohyoid, mylohyoid, anterior belly of digastric) or elevate the hyoid bone (posterior belly of digastric, stylohyoid). The sternocleidomastoid muscle (Fig. 6) is a large muscle located in the anterolateral portion of the neck. As previously described, it extends obliquely up the neck from the manubrium (sternal head) and medial third of the clavicle (clavicular head) to the mastoid process of the temporal bone. Its main actions are to flex the head and tilt the head. It is crossed superficially by the external jugular vein, and it covers the great vessels of the neck. The platysma muscle is a wide, thin quadrilateral muscle that covers the front and side of the neck and the lower face. The important muscle in the posterior part of the neck is the trapezius (Fig. 7), which is a wide, thin, and triangular muscle extending from the spinous processes of C7 and T1 to T10 to the clavicle (posterior lateral third), the acromion, and the scapula. Its action is to elevate and rotate the scapula. The bony skeleton of the neck consists of the upper sternum, clavicles, first ribs, and cervical vertebrae. The upper sternum is called the ‘‘manubrium’’; its superior surface is indented by a depression, suprasternal or jugular notch. On each side of this notch is the articular facet for the articulation of the medial end of the clavicle (see Fig. 4). Part of the sternodeidomastoid muscles originates from the anterior surface of the manubrium. The clavicle or collarbone extends from the manubrium (sternoclavicular joint) to the
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C2 Scalenus anterior muscle
C3
Scalenus medius muscle
C4
C5 Scalenus posterior muscle
C6
C7
Scalene tubercle
First rib
Second rib
Fig. 3. The origin and insertion of the scalene muscles. Note that the anterior scalenus and middle scalenus insert on the first rib, whereas the posterior scalenus inserts on the second rib.
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DESLAURIERS
C1
C2
Origins of Scalenus medius muscle
C3
C4 C5
Insertion of Scalenus medius muscle
Origins of Scalenus anterior muscle
C6 C7
Scalenus anterior muscle Scalenus medius muscle Scalenus posterior muscle
Insertion of Scalenus anterior muscle
First rib
Clavicle Second rib
Fig. 4. Topographic anatomy of the scalene muscles. The scalene muscles descend obliquely from the transverse processes of the cervical vertebrae to the first two ribs.
acromion of the scapula laterally (acromioclavicular joint). This latter articulation connects the upper limb to the chest wall. The clavicle is important for the stability of the shoulder–girdle complex. The acromioclavicular joint, whose construction is reinforced by the powerful coracoclavicular ligament, provides mobility between clavicle and scapula [5]. In their original description of the anterior transcervical–thoracic approach for the resection
of Pancoast tumors, Dartevelle and colleagues [6] recommended that the medial half of the clavicle be resected to gain better surgical exposure. Because the clavicle is the site of insertion of the sternocleidomastoid muscle (superior surface) and of the pectoralis major muscle (inferior surface), and because it stabilizes the shoulder girdle, its resection can lead to shoulder instability, especially when the clavicular resection is associated with first rib resection and cervical
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Box 3. Infrahyoid muscles (strap muscles) Superficial plane Sternothyroid Extends from sternum to thyroid cartilage Located deep to sternohyoid muscle Omohyoid Extends from the hyoid bone to the scapula Has two bellies united by a tendon Deep plane Thyrohyoid Continuation of sternothyroid muscle up to the hyoid bone Sternohyoid Anterior to sternothyroid and thyrohyoid Extends from clavicle to hyoid bone
vertebra resection. Because clavicular resection also can lead to serious alterations of shoulder mobility, cervical posture, and discomfort, most thoracic surgeons now advocate the transmanubrial approach described by Grunenwald and Spaggiari [7]. This approach spares the clavicle and all its muscular insertions while affording excellent access to the supraclavicular region. The first rib is important for maintaining stability of the shoulder girdle. It is the shortest, broadest, and most curved of all ribs, and it extends from the lateral margin of the manubrium inferior to the clavicular notch to a single-facet articulation with the body of the first thoracic vertebra. The first rib has a prominent scalene tubercle on the inner border of its superior surface for the insertion of the scalene anterior muscle. This site of insertion is important because the scalene triangle located between the scalene anterior muscle anteriorly, the scalene medius muscle posteriorly, and the first rib inferiorly allows the passage of the subclavian artery and brachial plexus. The subclavian vein crosses the first rib in front of the scalene tubercle and scalene anterior muscle. The cervical spine is made of seven vertebrae (C1–C7), the first one being called the ‘‘atlas,’’ the second one the ‘‘axis,’’ and the seventh the ‘‘vertebra prominens’’ because of its long spinous process that can be palpated easily and seen
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through the skin. Their distinctive feature is their transverse process, which circumscribes the transverse foramen through which the vertebral arteries and veins pass. The sixth cervical vertebra has a prominent anterior tubercle of its transverse process called the ‘‘tubercle de Chassignac,’’ which has a close relationship with the common carotid artery.
Topographic anatomy of the neck: anterior and posterior triangles Topographically, the neck is divided into an anterior and a posterior triangle by the sternocleidomastoid muscle (see Box 1 and Fig. 2). Complete knowledge of the anatomy of these triangles is important for the thoracic surgeon operating in the area, because they contain many important structures that must be identified and preserved during surgery. Superior sulcus tumors located anteriorly and extending in front of the anterior scalene muscle, for example, may invade the subclavian and internal jugular veins, whereas tumors extending between the anterior and medius scalene muscles may invade the phrenic nerve, the subclavian artery and its branches, and the brachial plexus [8]. The general shape of the posterior triangle of the neck is that of a triangle whose base is the middle third of the clavicle and whose apex is the meeting of the sternocleidomastoid muscle and trapezius muscles on the superior nuchal line. Its exact boundaries are presented in Box 1. The floor of the posterior triangle is made of four muscles, including the scalenus medius and scalenus posterior, which are covered by a deep cervical fascia. The inferior belly of the omohyoid muscle divides the posterior triangle into an occipital triangle (superior to the omohyoid) and a supraclavicular triangle that is crossed superficially by the external jugular vein. The anterior triangle of the neck, whose apex is the sternal notch and whose base is the inferior border of the mandible, contains the common carotid artery and its division into external and internal branches (carotid triangle).
Topographic anatomy of the neck: the root of the neck The root of the neck, the thoracocervical region, is bounded laterally by the first ribs, anteriorly by the sternal notch and manubrium,
536
DESLAURIERS
Anterior belly of digastric muscle
Mylohyoid muscle
Stylohyoid muscle Thyrohyoid muscle
Posterior belly of digastric muscle
Sternocleidomastoid muscle (cut) Sternohyoid muscle
Sternothyroid muscle
Anterior belly of omohyoid muscle Posterior belly of omohyoid muscle
Fig. 5. Topography of the infrahyoid and suprahyoid muscles. Note the two bellies of the omohyoid muscle united by an intermediate tendon.
and posteriorly by the first dorsal vertebra (D1). Its general arrangement is shown diagrammatically in Fig. 8. Veins and thoracic duct When Pancoast tumors are resected through the anterior cervical approach, the venous system
(Fig. 9) at the root of the neck (Box 5) is usually dissected first. Most of the external jugular vein is located in the posterior triangle of the neck, where it runs downward crossing the sternocleidomastoid muscle obliquely to empty into the subclavian vein. The anterior jugular vein’s anatomy is variable as it arises from submental venous plexuses and
ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Box 4. Suprahyoid muscles (connect the hyoid bone to the skull) Deep layer Geniohyoid: Extends from inferior maxillary to the hyoid bone Middle layer Mylohyoid Large and thin muscle that supports the floor of the mouth Located above the anterior belly of digastric muscle Superficial layer Stylohyoid: Small strip of muscle located along the upper border of posterior belly of digastric Digastric Has two bellies (anterior, posterior) joined by an intervening tendon Anterior belly arises from mandible Posterior belly arises from mastoid process
drains into the external jugular vein posterior to the sternocleidomastoid muscle. The subclavian vein begins on the lateral border of the first rib and crosses that rib anterior to the scalenus anterior muscle (anterior to scalene tubercle). On the medial border of the scalenus anterior muscle it joins the internal jugular vein to form the innominate vein. The internal jugular vein is the largest vein of the neck. It begins in the posterior cranial fossa, where it drains blood from the brain, and runs inferiorly lateral to the carotid artery (carotid sheath) in the anterior triangle of the neck. It then passes deep to the sternocleidomastoid muscle to unite with the subclavian vein to form the innominate vein posterior to the sternal end of the clavicle. On the left side, the thoracic duct, which ascends from the mediastinum, empties in the venous system at the union of the left internal jugular vein and subclavian vein. When Pancoast tumors are resected through the cervicothoracic approach, all branches of the subclavian vein must be visualized clearly, and proximal and distal control should be obtained early during the dissection. If the subclavian vein
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is invaded by the tumor, it can be resected without a need for reconstruction. On the left side, ligation of the thoracic duct usually is required. Arteries of the root of the neck The right subclavian artery (Box 6) is a terminal branch of the innominate artery. The left subclavian artery originates directly from the aortic arch. Both arteries enter the root of the neck behind their respective sternoclavicular joints. Each artery then arches superiorly and posteriorly behind the scalenus anterior muscle. Three branches of the subclavian artery originate in the sternocleidomastoid region. The first and most important one is the vertebral artery, which arises in the first portion of the artery medial to the anterior scalenus muscle. Next to the vertebral branch and also medial to the scalene anterior muscle is the thyrocervical trunk, which gives rise to the inferior thyroid artery and to the ascending cervical branch that supplies the muscles of the posterior triangle of the neck. The internal mammary branch arises from the inferior aspect of the subclavian artery opposite the thyrocervical trunk. It runs downward into the thorax parallel to the sternum. During surgery for Pancoast tumors, the subclavian artery and its branches must be dissected. This maneuver is much easier when the operation is done from above, through the anterior supraclavicular approach. If necessary, the subclavian artery can be resected locally and reconstruction performed either with an end-to-end anastomosis or graft interposition. The vertebral artery never should be sacrificed unless the continuity of the circle of Willis has been well documented preoperatively. Nerves of the root of the neck From the skull, the vagus nerve passes inferiorly through the neck within the carotid sheath behind the internal carotid artery and internal jugular vein. At the base of the neck, the right vagus nerve crosses the origin of the right subclavian artery behind the sternoclavicular joint, where it gives off the right recurrent laryngeal nerve (inferior laryngeal nerve) that loops around and under the subclavian artery (Figs. 10 and 11). This nerve ascends in the tracheoesophageal groove (Box 7), where it can be injured during extensive cervicomediastinal dissections done for tumors located near or at the
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DESLAURIERS
Posterior belly of digastric muscle
Anterior belly of digastric muscle
Posterior scalene muscle
Anterior belly of omohyoid muscle
Middle scalene muscle
Sternocleidomastoid muscle
Posterior belly of omohyoid muscle Anterior scalene muscle
Fig. 6. Lateral view of the neck muscles showing the sternocleidomastoid muscle.
thoracic inlet. On the left side, the recurrent laryngeal nerve originates close to the ligamentum arteriosum where it courses around the aortic arch from front to back before ascending to the neck, also in the tracheoesophageal groove. On each side, the recurrent nerves accompany the laryngeal branch of the inferior thyroid artery deep to the inferior constrictor muscle of the pharynx behind the cricothyroid articulation. Before entering the larynx, each recurrent nerve sends off 8 to 14 short branches into the lateral wall of the esophagus; these branches sometimes can be
seen when operating on the upper esophageal sphincter. The recurrent nerves supply all of the intrinsic muscles of the larynx except the cricothyroid muscle. In general, the right recurrent nerve has a more asymmetrical and diagonal course than the left recurrent nerve, and this course is one of the reasons most surgeons choose the left thoracic inlet as the venue for transposing colon or stomach [9,10]. The superior laryngeal nerves arise from the vagus nerves in the neck behind the upper portion
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ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Sternocleidomastoid muscle
Rhomboideus minor muscle
Trapezius muscle
Rhomboideus major muscle
Latissimus dorsi muscle
Fig. 7. Topography of the trapezius muscle.
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DESLAURIERS
C5
Scalenus anterior muscle
C6 Phrenic nerve
C7 C8
T1 Superior trunk of brachial plexus Clavicle
Middle trunk of brachial plexus Lower trunk of brachial plexus
Cords of brachial plexus
First rib
Subclavian artery
Subclavian vein
Fig. 8. General anatomy of the cervicothoracic region (the root of the neck).
of the triangle made by the carotid artery bifurcation and almost immediately divide into two terminal branches. The internal laryngeal nerve pierces the thyrohyoid membrane with the superior laryngeal artery; the external branch accompanies the superior thyroid artery posterior to the sternothyroid muscle. The phrenic nerve arises from C3-to-C5 (the main root arises from C4) and descends obliquely in the neck on the anterior surface of the scalenus anterior muscle. At the base of the neck, it is
located over the medial surface of this muscle, 3 to 4 cm lateral to the sternoclavicular joint. The phrenic nerve descends posterior to the subclavian vein and anterior to the internal mammary artery to enter the thorax. Surgically, the phrenic nerve can be accessed by a transverse incision made over the posterior border of the sternocleidomastoid muscle 2 fingerbreadths above the clavicle. With the sternocleidomastoid muscle and internal jugular vein retracted medially, the phrenic nerve can be seen
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Scalenus medius muscle
Scalenus anterior muscle Facial vein
External jugular vein
Sternocleidomastoid muscle
Internal jugular vein
Anterior jugular vein Omohyoid muscle (inferior belly)
Subclavian vein Innominate vein Fig. 9. Veins at the root of the neck.
over the anterior surface of the scalene anterior muscle. It can be injured during a prescalene nodal biopsy for the purpose of staging lung cancer [11,12], because the floor of the prescalene space is formed by the scalenus anterior muscle with the phrenic nerve lying in its sheath. During resection of a Pancoast tumor through the cervicothoracic approach, every attempt should be made to preserve the phrenic nerve; for this reason the scalene anterior muscle must be divided as close to its site of insertion on the first rib as possible. The cervical sympathetic trunks (see Fig. 10) are made of three sympathetic ganglia (Box 8) joined by intermediate longitudinal strands of nerve fibers. There structures are located on the
prevertebral fascia, which separates them from the transverse processes of the cervical vertebrae. The superior ganglion is large and fusiform and is located at the level of the second and third cervical vertebrae. The middle cervical ganglion is small and inconsistent and is located at the level of the sixth cervical vertebra. The inferior cervical ganglion or stellate ganglion lies anterior to the transverse process of C7 near the superior border of the neck of the first rib. The stellate ganglion also is known as the ‘‘cervicothoracic ganglion’’ because it is generally fused with the first thoracic ganglion. Although it is called the ‘‘stellate ganglion,’’ its form can be quite variable (eg, semilunar or circular), and indeed it is seldom starshaped.
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DESLAURIERS
Box 5. Veins at the root of the neck
Box 6. Arteries at the root of the neck
External jugular vein Drains mandibular and auricular regions Located in posterior triangle of the neck Empties into subclavian vein
Right subclavian artery Originates from the innominate artery Enters the root of the neck behind the sternoclavicular joint
Anterior jugular vein Drains submental regions Variable anatomy Empties into internal jugular vein
Left subclavian artery Originates from the aortic arch Ascends and enters the root of the neck behind the left sternoclavicular joint
Subclavian vein Continuation of axillary vein Crosses the first rib anterior to the scalene anterior muscle
Branches of the subclavian arteries Vertebral: Arises medial to the scalenus anterior muscle Thyrocervical trunk: Gives rise to inferior thyroid and ascending cervical branches Internal mammary: Arises from inferior aspect of subclavian artery Descends inferomedially into the thorax
Internal jugular vein Drains blood from the brain Runs inferiorly lateral to the common carotid artery Crosses deep to the sternocleidomastoid muscle to unite with the subclavian vein
Fascia and fascial spaces of the neck The fascial planes (Box 9) and spaces (Box 10) of the neck are important to the thoracic surgeon because they connect the mediastinum with the neck, and air (pneumomediastinum) or infection (mediastinitis) can travel that route. The fascia of the neck comprise three layers, the superficial or investing fascia, the middle or pretracheal fascia, and the posterior or prevertebral fascia. The superficial (investing) fascia is deep to the subcutaneous fascia and encircles the neck completely, investing the platysma, sternocleidomastoid, and trapezius muscles. Superiorly it is attached to the superior nuchal line and spinous processes of the cervical vertebrae, and inferiorly it is attached to the manubrium, clavicle, and scapula. Superior to the sternal notch, this fascia splits into two layers that are attached to the anterior and posterior manubrium. The space between these two layers, the suprasternal space or space of Burns, contains the sternal heads of the sternocleidomastoid muscles and the arch of the internal jugular vein. The middle or pretracheal fascia extends from the thyroid and cricoid cartilages down into the thorax. It is an extensive fascia that
splits to surround the thyroid gland, trachea, and esophagus completely. It invests the strap muscles, and laterally it fuses with the superficial fascia opposite the carotid sheath. In cases of spontaneous pneumomediastinum, interstitial air usually reaches the neck by dissecting along this fascia [13]. The posterior cervical fascia consists of two layers. The first or alar fascia lies posterior to the visceral compartment of the neck and continues laterally to form the carotid sheath. The second or prevertebral fascia extends from the base of the skull to the third thoracic vertebra and covers the prevertebral muscles. There are two cervicothoracic spaces (Fig. 12) of importance to the thoracic surgeon, the previsceral or pretracheal space and the retrovisceral or retropharyngeal space (see Box 10). The pretracheal space, which lies beneath the strap muscles, is opened during mediastinoscopy, thyroid surgery, and surgery of the cervical trachea. It extends from the thyroid cartilage above to the upper border of the aortic arch where it terminates by adhesions extending from the fibrous pericardium to the posterior surface of the manubrium. These fibrous adhesions form
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Superior cervical ganglion Vagus nerve (CN X) Sympathetic trunk
Middle cervical ganglion Common carotid artery Scalenus anterior muscle Cupula Phrenic nerve
Inferior cervical (Stellate) ganglion Vertebral artery
Subclavian artery
Ansa subclavia
Right recurrent laryngeal nerve
Fig. 10. Arteries and nerves at the root of the neck.
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DESLAURIERS
Superior laryngeal nerve
Left vagus nerve (CN X) Right vagus nerve (CN X) Trachea
Right recurrent laryngeal nerve
Left recurrent laryngeal nerve
Esophagus
Fig. 11. Anatomy of the left and right recurrent laryngeal nerves.
ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Box 7. Anatomy of the recurrent laryngeal nerves (inferior laryngeal nerves) Right recurrent laryngeal nerve Loops around the right subclavian artery Ascends in tracheoesophageal groove Has a more asymmetric and diagonal course than the left recurrent nerve Left recurrent laryngeal nerve Loops around the aortic arch near the ligamentum arteriosum Ascends in the tracheoesophageal groove
a relative barrier to the downward gravitational spread of infection. The retrovisceral or retropharyngeal space consists of loose connective tissue located in front of the prevertebral fascia. It extends from the skull through the neck and posterior mediastinum down to the diaphragm. Laterally, it seals off at the transverse processes of the cervicothoracic vertebrae. This space is of considerable importance, because retropharyngeal abscesses secondary to oropharyngeal infections can spread to the mediastinum producing a diffuse necrotizing mediastinitis [14,15].
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Box 9. Fascias of the neck Superficial (investing) fascia Encircles the neck completely Attached superiorly to superior nuchal line and spinous processes of C1–C7 Attached inferiorly to manubrium, clavicle, and scapula Middle (pretracheal) fascia Extends from thyroid and cricoid cartilages down into the thorax Splits to surround the thyroid, trachea, and esophagus completely Posterior (prevertebral) fascia Extends from the base of the skull to the third thoracic vertebra Covers prevertebral muscles
Box 10. Cervicothoracic fascial spaces Pretracheal (previsceral) space Located between trachea and strap muscles and between trachea and posterior manubrium Extends from thyroid cartilage to upper border of aortic arch (T4) Retropharyngeal (retrovisceral) space Located in front of the prevertebral fascia Extends from the skull to the diaphragm
Box 8. Sympathetic ganglia of the neck Superior cervical ganglion Large and fusiform Located at the level of C2, C3 Middle cervical ganglion Small and inconsistent Located at the level of C6 Inferior cervical ganglion (stellate ganglion) Generally fused with the first thoracic ganglion Located at the level of C7 Seldom star-shaped
Summary All thoracic surgeons must have an extensive knowledge of the anatomy of the neck, because cervical approaches are used on an almost daily basis to access the cervical trachea, upper esophagus, and superior mediastinum. In addition to basic and scholarly knowledge of anatomy, they also must understand the anatomic relationships among the neck, the mediastinum, and both pleural spaces. Indeed, such knowledge forms the basis for the diagnosis and management of many aspects of pulmonary, mediastinal, and esophageal pathologies.
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DESLAURIERS
Previsceral space
Retrovisceral space
Fig. 12. The anatomy of the previsceral and retrovisceral spaces.
ANATOMY OF THE NECK AND CERVICOTHORACIC JUNCTION
Further readings Moore KL. Clinically oriented anatomy. 2nd edition. Baltimore (MD): Williams and Wilkins; 1985. Gardner E, Gray DJ, O’Rahilly R. Anatomy: a regional study of human structure. 3rd Edition. Philadelphia: WB Saunders Co; 1969.
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