Fig. 1.1
Transverse section of sheep neck. Clearly evidence of anterior and posterior compartments
Similarly the human larynx has the function of air passage, phonation, and sphincter. It extends from the tongue to the trachea.
The ipopharynx is located posterior to the larynx and continues into the esophagus; the prevertebral muscles divides anterior and posterior compartements of the neck.
The larynx is covered superficially by infrahyoid muscles from the cervical bands and skin.
Before starting with neck dissection, it is useful to identify skin landmark of larynx framework (Fig. 1.2).
Fig. 1.2
Skin landmarks are hyoid bone (HB), thyroid cartilage (ThC), cricoid cartilage (CrC), and trachea (Tr). Superficial cervical fascia (arrow)
After skin incision there is a subcutaneous tissue composed of skin subcutaneous tissue and cutaneous colli muscle which is similar to platysma muscle (Fig. 1.3).
Fig. 1.3
Evidence of mid cervical fascia. The arrow underlines the cutaneous colli muscle included into the superficial flap (arrow)
The superficial cervical fascia (Fig. 1.2) is quite thicker than the human one but nevertheless is easily dissected with a scalpel or a pair of scissors in order to expose the mid cervical fascia.
The mid cervical fascia is thinner than the superficial one and surrounds the larynx and the infrahyoid compartment (Fig. 1.3).
By opening up the mid cervical fascia, we can approach the infrahyoid region which contains the infrahyoid muscles and the larynx framework (Fig. 1.4).
Fig. 1.4
Dissection of mid cervical fascia
The larynx is surrounded laterally by the great vessels, sternomastoid muscle and the submandibular glands (Figs. 1.5, 1.6, and 1.7).
Fig. 1.5
Lateral view. On the midline evidence of larynx in particular thyroid cartilage (ThC) and trachea (Tr). The mid cervical fascia (MCF) was dissected on the midline and preserved at the inferior part in order to show how it surrounds neck structures. Lateral to the larynx evidence of sternomastoid muscle (SMM), external jugular vein (EJV), and its branches: maxillary (MB) and occipital (OB). Submandibular gland (SG) is also visible in relationship with the maxillary branch of the external jugular vein
Fig. 1.6
Evidence of the neurovascular bundle (NVB) formed by carotid artery, internal jugular vein, and vagus nerve. The external jugular vein (EJV) and submandibular gland (SG) are located more superficially and laterally. Thyroid vein (ThV) arises from jugular vein and reaches the thyroid gland
Fig. 1.7
(a) Evidence of prevertebral muscles (PreV M) on posterior plane. The esophagus (Es) lies on the posterior wall of the larynx and trachea (Tr). Carotid artery (CA) is located laterally to the larynx (b) Trachea (Tr) was dissected from esophagous (Es)
Caudal laryngeal nerve in the sheep is similar to recurrent laryngeal nerve (RLN) of human. To simplify the explanation, caudal laryngeal nerve is called RLN.
RLNs lie into tracheoesophageal groove (Fig. 1.8) and pass behind the thyroid gland (TG) before getting into the larynx through the cricothyroid membrane (Fig. 1.9). Its direction is comparable to the one in the human specimen.
Fig. 1.8
(a) RLN runs into the tracheoesophageal groove. The nerve lies between the trachea (Tr) and the esophagus (Es). (b) RLN course in human dissection. RLN is covered by fascia (arrow). Fascial layer has been dissected showing RLN immediately below
Fig. 1.9
RLN passes behind the thyroid gland (TG). Evidence of the thyroid vein (ThV) going toward the inferior pole of the thyroid gland
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