Dissection Of The Carotid Sheath

The carotid sheath is a fascial envelope surrounding the internal jugular vein, common carotid artery, and vagus nerve (Fig. 2-3). It is interposed between the superficial and prevertebral layers of the cervical fascia. The carotid sheath must be included in the resection, preserving its neuro-vascular contents.

Figure 4-42 The whole specimen is now anterior to the sternocleidomastoid muscle. Note the anterior (a) and posterior (p) branch of the cervical plexus. The anterior branches must be sectioned (arrow) to continue the dissection toward the carotid sheath (right side). SC, sternocleidomastoid muscle; US, upper part of the specimen (submandibular, upper jugular, and upper spinal accessory areas); LS, lower part of the specimen (supraclavicular fossa).

Figure 4-42 The whole specimen is now anterior to the sternocleidomastoid muscle. Note the anterior (a) and posterior (p) branch of the cervical plexus. The anterior branches must be sectioned (arrow) to continue the dissection toward the carotid sheath (right side). SC, sternocleidomastoid muscle; US, upper part of the specimen (submandibular, upper jugular, and upper spinal accessory areas); LS, lower part of the specimen (supraclavicular fossa).

Figure 4-43 Lateral view of the deep branches of the cervical plexus that have been preserved on the right side. SC, sternocleidomastoid muscle; IJ, internal jugular vein; deep branches of the cervical plexus.

This part of the dissection needs a new number 10 knife blade and adequate tension. The surgical specimen is grasped with hemostats and retracted medially by the assistant, while the surgeon uses one hand with a gauze pad to pull laterally over the deep cervical muscles. This allows a complete exposure of the carotid sheath along the entire length of the surgical field. To avoid injuring important neurovascular structures, during the next minutes all movements should

Figure 4-44 The right sympathetic trunk is exposed posterior to the carotid sheath. st, sympathetic trunk; IJ, internal jugular vein; SC, sternocleidomastoid muscle.

be precise and gentle. This includes all activity from the assistants, scrub nurse, and circulating personnel in the operating room.

An incision is made with the scalpel over the vagus nerve along the entire length of the carotid sheath (Fig. 4-45). The nerve can be easily identified between the internal jugular vein and the carotid artery (Fig. 4-46). The dissection then continues, removing the fascia from the internal jugular vein. This is achieved by continuously passing the knife blade along the wall of the internal jugular vein up and down along its entire length (Fig. 4-47). The scalpel must be moved obliquely

Figure 4-45 The carotid sheath should be opened by cutting over the vagus nerve. ca, carotid artery; vn, vagus nerve; S, specimen.

Carotid Sheath
Figure 4-46 Dissection of the carotid sheath on the right side. CA, carotid artery; IJ, internal jugular vein; vn, vagus nerve; st, sympathetic trunk; SC, sternocleidomastoid muscle.

Figure 4-47 Dissection of the carotid sheath on the right side. CA, carotid artery; IJ, internal jugular vein; vn, vagus nerve; oh, omohyoid muscle; SC, sternocleidomastoid muscle; uf, upper fold of the internal jugular vein wall; lf, lower fold of the internal jugular vein wall; deep branches of the cervical plexus.

Figure 4-47 Dissection of the carotid sheath on the right side. CA, carotid artery; IJ, internal jugular vein; vn, vagus nerve; oh, omohyoid muscle; SC, sternocleidomastoid muscle; uf, upper fold of the internal jugular vein wall; lf, lower fold of the internal jugular vein wall; deep branches of the cervical plexus.

with respect to the vein, with the blade pointing away from the vein wall. When this is properly done and the traction exerted on the tissue is adequate, this maneuver is extremely safe and effective. The fascia can be seen coming apart from the vein after each pass of the knife blade, until the internal jugular vein is completely released from its fascial covering (Fig. 4-48).

The facial, lingual, and thyroid veins appear as the dissection approaches the medial wall of the internal jugular vein (Fig. 4-49). They should be clearly identified, ligated, and divided to complete the isolation of the internal jugular vein. Other smaller branches as well as some vasa vasorum often found during the dissection of the internal jugular vein can be cauterized, taking care not to use the cautery too close to the venous wall to avoid troublesome perforations that will require further repair. Bipolar cautery may be helpful at this stage of the operation.

The dissection of the carotid sheath has two danger points. One at each end—upper and lower—of the dissection (Fig. 4-47). At these two points the traction exerted to facilitate the dissection of the fascial envelope produces a folding of the wall of the internal jugular vein that can be easily sectioned at the touch of the scalpel blade. We refer to these two points as the initial folds, and they should be freed before further dissection of the internal jugular vein is attempted. The surgeon must be extremely cautious to avoid injuring the vein at these points.

Lower in the neck, the terminal portion of the thoracic duct on the left side (Fig. 4-50), and the right lymphatic duct, when present, are also within the boundaries of the dissection and must be preserved. They are difficult to identify because of their variable anatomy and, more often than desired, can only be found after being injured, which is especially likely given their very thin wall that easily breaks under normal dissection maneuvers. The surgeon must be aware that postoperative leakage in patients with functional neck dissection is much more difficult to solve than in patients with radical neck dissection because of the preservation of the sternocleidomastoid muscle. The pressure maneuvers that usually control chylous fistulae in patients with radical neck dissection are less effective when the muscle remains in place. Thus, intraoperative recognition of the problem and appropriate management at the time of operation are essential for a

Carotid Artery Dissection
Figure 4-48 Dissection of the internal jugular vein within the carotid sheath (right side). ca, carotid artery; IJ, internal jugular vein; vn, vagus nerve; oh, omohyoid muscle; sh, sternohyoid muscle; SC, sternocleidomastoid muscle; FC, fascia of the carotid sheath.
Omohyoid Muscle
Figure 4-49 Lateral view of the veins draining into the medial face of the right internal jugular vein. IJ, internal jugular vein; SC, sternocleidomastoid muscle; oh, omohyoid muscle; st, sternothyroid muscle; FC, fascia of the carotid sheath.
Figure 4-50 Cervical course of the thoracic duct on the left side of the neck, td, thoracic duct; IJ, internal jugular vein; CA, carotid artery; SA, subclavian artery; va, vertebral artery; it, inferior thyroid artery; as, anterior scalene muscle; pn, phrenic nerve; vn, vagus nerve.

successful outcome. Once injured, the thoracic duct must be surrounded by muscle, fascia, or adipose tissue before being sutured. More details about the management of the thoracic duct can be found in Chapter 5.

Once the internal jugular vein is released from its covering fascia, the dissection continues medially over the carotid artery. The specimen is now completely separated from the great vessels and remains attached only to the strap muscles (Fig. 4-51). The dissection of the strap muscles will complete the release of the neck dissection specimen. However, when the strap muscles are to be removed with the primary tumor, an en bloc resection may be performed by leaving the specimen pedicled over the strap muscles in order to resect the primary tumor in-continuity with the neck dissection specimen.

0 0

Post a comment