Lab Manual - Posterior Triangle of the Neck

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Identify the boundaries of the posterior cervical triangle and its subdivisions. (explanation)
  2. Identify the scalene muscles and the first rib and relate them to the neurovascular structures at the root of the neck. (explanation)
  3. Identify and list the parts and branches of the subclavian artery and vein, and describe their course in the neck. (explanation)
  4. Identify the neurovascular entities that have different relationships to structures on the right and left sides of the root of the neck. (explanation)
  5. In the root of the neck, locate the vagus and phrenic nerves and describe their relationships to the organs, fascia, vessels, and viscera of the neck. (explanation)
  6. Identify the deep cervical lymph nodes and explain their significance. (explanation)

Readings and Modules:

Procedure:

1. Review the bony landmarks. (Play movie; View images: N 4, 6, 8, 186A, 186C, TG 7-06, 7-08, 7-32, 7-15A, 7-15B)

On the base of a skull locate the following structures: foramen magnum, occipital condyles, hypoglossal canal, jugular foramen, external opening of the carotid canal, styloid process.

Surface anatomy of the anterior neck

Examine the first rib on the skeleton and cadaver, and note grooves for the subclavian vein and artery and attachments for the scalene muscles. Review the arrangement of rib one and sternum at the entrance to the thorax (root of neck). If still present, the middle third of the clavicle should be removed for better visibility.

2. Locate the accessory nerve and the roots of the cervical plexus. (Play movie; View images: N 28, 32A, 32B, 35, 71, 72, 127, 129, TG 7-02A, 7-02B, 7-10, 7-12, 7-16, 7-17, 7-18, 7-93)

Review the boundaries of the posterior triangle and its subdivisions. Reflect the sternocleidomastoid muscle to the mastoid and you will find the accessory nerve emerging at the posterior border at or just below the upper and middle thirds of the muscle and running obliquely down to the superior border of the trapezius muscle. The nerve is usually in the superficial layer of deep cervical fascia. Remove this fascia, leaving the nerves and the external jugular vein intact. Note the course of the accessory nerve through the muscle and its relation to all of the cutaneous branches of the cervical plexus (lesser occipital, great auricular, transverse cervical, supraclavicular nerves). Now trace these nerves to their cervical origins, identifying specific ventral primary rami of the spinal nerves (roots of the cervical plexus).

3. Follow the internal jugular vein to its termination noting its tributaries. (Play movie; View images: N 8, 31, 33, 70, 74, 126, 256, TG 7-06, 7-11, 7-13, 7-15, 7-16, 7-51, 7-73, 7-75)

Trace the internal jugular vein caudally and identify superior thyroid and, if present, middle thyroid tributaries. At what foramen on the base of the skull does the internal jugular vein originate? Note its junction with the subclavian vein to form either the right or left brachiocephalic vein. Trace the external jugular vein until it joins the subclavian vein. Identify, trace (in the posterior triangle), and remove the transverse cervical and suprascapular veins. Note that the junction of subclavian and internal jugular vein is posterior to the sternoclavicular joint.

4. Look for deep cervical lymph nodes and find the thoracic duct on the left. (Play movie; View images: N 34, 36, 39, 72, 74, 193, 239, 266, 430, TG 4-18, 4-44, 5-37, 7-10, 7-14, 7-15, 7-17, 7-18, 7-74)

Observe lymph nodes along the internal jugular vein and veins of the posterior triangle (transverse cervical and suprascapular veins). The omohyoid muscle divides the deep cervical nodes into superior and inferior groups. These nodes form a chain and end in the jugular trunk, which drains the deep cervical nodes to the venous circulation at the junction of the internal jugular and subclavian veins (via the right lymphatic duct on the right side and the termination of the thoracic duct on the left). Note the arch and course of the thoracic duct as it emerges behind the esophagus in the upper thorax. The duct frequently looks like a vein due to blood backing up into it during the embalming process. However, identify it by its characteristic position, arching immediately deep to the internal jugular vein and lying upon the anterior scalene muscle. The right lymphatic duct is small and difficult to find.

Cervical lymph node groups

Identify the prevertebral fascia and locate the anterior scalene muscle. Remove the scalene fascia; expose and trace the phrenic nerve (C3-5) to its roots.

5. Dissect the root of the neck to expose the subclavian arteries and their branches, the cervical sympathetic trunk and its ganglia, and the recurrent laryngeal nerve. (Play movie; View images: N 32, 33A, 33B, 35, 75, 76, 130, 131, 135, 136, 177, 186, 191, 196, 232, 427, 477, TG 1-13, 2-09, 2-15, 4-09, 4-15, 4-20, 7-10, 7-14, 7-15A,7-15B, 7-17, 7-19, 7-95)

Carefully clean the connective tissue from the root of the neck, exposing the brachiocephalic, common carotid, and subclavian arteries. Expose both subclavian arteries throughout their length, defining parts and noting vagus, cardiac, and phrenic nerves as they cross anterior to the arteries. Pull the carotid sheath and its contents to one side and identify the prevertebral fascia. Locate the sympathetic trunk passing posterior and medial to the subclavian artery; you may find a loop of the trunk (ansa subclavia) around the artery. Follow the course of the trunk along the medial border of the common carotid artery or deep in the prevertebral fascia. Can you identify the middle cervical ganglion? Locate the recurrent laryngeal nerve (a branch of the vagus), which curves around the subclavian artery on the right side to ascend in the tracheo-esophageal groove.

Organize those parts of the cervical sympathetic trunk you have seen so far. Do you see connections (gray rami communicantes) between the trunk or ganglia and spinal nerves?

Recall the location and the cervical relationship of first rib and pleura (cupula) to the subclavian vessels. Taking care not to disrupt the thoracic duct, cut the junction of the subclavian and internal jugular veins. Pull these veins aside to identify branches of the subclavian artery: vertebral (trace it to the transverse foramen of the 6th cervical vertebra and note relation to sympathetic trunk and ganglia); thyrocervical trunk (note location and relation to phrenic nerve and anterior scalene muscle); transverse cervical and suprascapular arteries. Are these individual arteries or are they derived from a common trunk? Trace their course across the phrenic nerve and the anterior scalene muscle and through the posterior triangle to where they have been seen in previous dissections. Note the origin of the inferior thyroid artery and its course to the thyroid gland. Study its relation to the sympathetic trunk and middle cervical ganglion. Trace the internal thoracic artery. It arises from the subclavian opposite the thyrocervical trunk. It is crossed anteriorly by the phrenic nerve. Trace the dorsal scapular artery, a branch of the 3rd part of the subclavian. It may also be a branch of the transverse cervical artery. Trace it through the brachial plexus.

Vessels of the root of the neck

6. Cut the anterior scalene muscle to expose the costocervical trunk, the roots of the brachial plexus and nerves arising from them. (Play movie; View images: N 30, 33A, 33B, 185, 186, 429, 430, 477, TG 2-13, 2-14, 7-15A, 7-15B)

On the right side, carefully cut through the anterior scalene muscle, elevate the artery and look for the costocervical trunk. Define the interscalene triangle, identify middle and posterior scalene muscles. Trace the trunks and roots of the brachial plexus within the interscalene triangle and complete your organization of the brachial plexus. Dissect the following: suprascapular nerve, dorsal scapular nerve and long thoracic nerve (the last two of which penetrate the middle scalene muscle). Note that the brachial plexus passes superior and posterior to the subclavian artery in the interscalene triangle. In forced inspiration, what muscle raises the second rib?