Neck Dissection (2) PDF

Head and neck dissection 1 Anterior neck 1) Begin by reviewing the surface anatomy of the region. On your cadaver, palpate the clavicle, sternoclavicular joint, jugular notch, manubrium, sternocleidomastoid, mastoid process, ramus of the mandible, angle of the mandible, body of the m...

Head and neck dissection 1 Anterior neck 1) Begin by reviewing the surface anatomy of the region. On your cadaver, palpate the clavicle, sternoclavicular joint, jugular notch, manubrium, sternocleidomastoid, mastoid process, ramus of the mandible, angle of the mandible, body of the mandible, mental protuberance, hyoid bone, thyroid cartilage, cricoid cartilage, and zygomatic arch. 2) You have previously reflected the skin over the lateral cervical region and began to identify and clean the sternocleidomastoid and platysma muscles. Attempt to arrange all tissue in the neck and upper thoracic wall back to its original, anatomic location. a) Make a midline incision from the mental protuberance to the jugular notch (See figure 1). The skin in the anterior neck is very thin so stay shallow. This is the anteromedial border of the anterior cervical triangle. Cut b) Now lift the skin flap you made in the lateral cervical region and continue reflecting the skin towards the inferior border of the mandible. This is the superior border of the anterior cervical triangle. Figure 1 3) Identify and clean the platysma. (See Gilroy, fig. 37.32) a) Review its attachments, actions, and innervation. b) Loosen the platysma from the investing fascia and reflect it superiorly toward the mandible. 4) Identify the sternocleidomastoid. a) Review its attachments, actions, and innervation. b) Recall that the external jugular vein and cutaneous branches of the cervical plexus, including the transverse cervical and great auricular nerves, should be passing anterior to the sternocleidomastoid. Preserve these structures as you clean the sternocleidomastoid. (See Gilroy, fig. 37.36D) c) Its anterior border is the posterolateral border of the anterior cervical triangle. 5) Anterior to the sternocleidomastoid, you may find some anterior jugular veins lying on the investing fascia of the neck. These superficial veins and the investing fascia can be removed to reveal the infrahyoid and suprahyoid muscles. Do not remove any vascular structures deep to the investing fascia. (See Gilroy, figs. 37.32, 37.35) a) Palpate for the hyoid bone. This should be lying just superior to the laryngeal prominence of the thyroid cartilage. b) Inferior to the hyoid bone, locate and clean the infrahyoid muscles. (See Gilroy, fig. 37.16) i) Identify the sternohyoid, sternothyroid, and omohyoid muscles. ii) Review their attachments, actions, and innervations. iii) Note the relationship of each of these muscles to each other; knowing this relationship will help you identify them correctly. iv) Superior to the sternothyroid, locate the thyrohyoid. v) Preserve any nerves entering these muscles. c) Superior to the hyoid bone, locate and clean the suprahyoid muscles. (See Gilroy, fig. 37.33) i) Identify the anterior and posterior bellies of the digastric muscle. (1) The mylohyoid will be found deep to the anterior belly of the digastric. (2) They stylohyoid will be found in close relation to the posterior belly of the digastric, its fibers splitting around the intermediate tendon of the digastric near their insertion on the hyoid. (3) Review their attachments, actions, and innervations. We will not see the origins of the stylohyoid and posterior belly of the digastric today. ii) Note the submandibular gland lateral to the anterior belly of the digastric. 6) Loosen the sternocleidomastoid from the investing fascia deep to it. Use a scissor to detach the sternocleidomastoid from its attachment on the manubrium and clavicle and reflect it towards its superior attachment on the mastoid process. Continue to preserve any branches of the cervical plexus. 7) Locate the carotid sheath deep to the sternocleidomastoid. (See Gilroy, figs. 37.33-37.35) a) The sheath may be partially open on the right from the embalming process. b) Identify the common carotid artery, internal jugular vein, and vagus nerve in the root of the neck.  c) Working from inferior to superior, use blunt dissection and scissors to clean the carotid sheath from these vessels. Work carefully as we are trying to locate smaller neurovascular structures contained within or in close relation to the carotid sheath. i) You should notice that the internal jugular vein lies lateral to the common carotid artery and the vagus nerve is situated between these vessels. ii) The internal jugular vein gives rise to the facial vein. Preserve the facial vein as it crosses the inferior border of the mandible into the face. You may remove any branches off the facial vein in the anterior neck. iii) The ansa cervicalis is the muscular portion of the cervical plexus. (1) It appears as a loop just inferior to the bifurcation of the common carotid artery, with the superior root of the loop descending anteriorly to the internal carotid artery and the inferior root descending posterior to the internal carotid artery. (2) If you found any nerve branches going to the infrahyoid muscles, trace these back to find the ansa cervicalis. iv) The common carotid artery typically bifurcates into external and internal carotid arteries around the C4-C5 vertebral level and roughly in line with the laryngeal prominence. (1) The internal carotid artery will be the more posterior of the two branches. (a) Note the slight enlargement of the proximal portion of the internal carotid artery that is the carotid sinus. (b) Clean the internal carotid artery as far superiorly as possible. (2) The external carotid artery will be the more anterior of the branches. As you clean it, look for its branches. (a) Today, you should expect to find: the superior thyroid artery, lingual artery, facial artery, and occipital artery. (b) We will study more proximal branches later. 8) Running with the superior thyroid artery, find the superior laryngeal nerve from the vagus nerve. We will look for its internal and external branches when we study the pharynx and larynx. Follow the superior thyroid artery to the thyroid gland. 9) Near the lingual artery, find the hypoglossal nerve (CN XII). a) It should be coursing anterolateral to the carotid arteries and should give off the superior root of the ansa cervicalis as it passes over the internal carotid artery. b) You may also be able to find the C1 branch coming off of the hypoglossal nerve going to the thyrohyoid muscle. 10) The facial artery can be found entering the submandibular gland before crossing the mandible into the face.