The anatomical description of the fascial layers of the neck has suffered a number of different descriptions. For practical reasons we will consider two distinct fascial layers in the neck, the superficial cervical fascia and the deep cervical fascia. The superficial cervical fascia corresponds to the subcutaneous tissue. The deep cervical fascia is the key element for functional and selective neck dissection.
The superficial cervical fascia extends from the zygoma down to the clavicle, enveloping the platysma muscle and the muscles of facial expression. There is a potential space between the superficial fascia and the deep fascia that allows free movement of the skin and superficial fascia on deeper structures. This plane, located underneath the platysma muscle, is the cleavage plane that should be followed to properly elevate the cutaneous flaps in functional and selective neck dissection as well as other surgical procedures in the neck.
The deep cervical fascia surrounds the neck, enveloping its different structures. For teaching purposes, two different layers are considered within the deep cervical fascia: a superficial and a deep or prevertebral layer. The carotid sheath, which is an important structure from the surgical standpoint, is located between the two layers of the deep cervical fascia.
The superficial layer of the deep cervical fascia, also known as investing or anterior fascia, completely envelops the neck with the exception of the skin, platysma muscle, and superficial fascia (Fig. 2-1). It is attached to the occipital protuberance, mastoid process, capsule of the parotid gland, angle of the jaw, and body of the mandible to the symphysis, where it proceeds around the opposite side in a similar manner. It then goes posteriorly across the spinal process of the cervical vertebrae and the ligamentum nuchae. Anteriorly, it passes from the mandible to the hyoid bone and from here down to the sternum. Inferiorly, it attaches to the sternum, upper edge of the clavicle, acromion, and spine of the scapula. At the inferior border, in the midline, the superficial layer splits in two different layers just superior to the manubrium of the sternum. The space between these two layers is known as the suprasternal space of Burns. From posterior to anterior, the superficial layer splits to enclose the trapezius, the portion of the omohyoid muscle that crosses the posterior triangle of the neck, and the sternocleidomastoid muscle. In a similar way it envelops the strap muscles, before ending in the midline. The superficial veins of the neck lie on or within this superficial layer of the deep cervical fascia.
The deep or prevertebral layer, like the superficial layer, attaches posteriorly at the spinous process of the cervical vertebrae and ligamentum nuchae (Fig. 2-2). At its upper limit, it goes to the skull base at the jugular foramen and carotid canal, then passes across the basilar process to the opposite side. This fascial layer covers the muscles of the back that enter into the neck immediately deep to the trapezius muscle (splenius and levator scapula). At this level there is a potential space between both layers. At the upper limit of the posterior triangle, this space is almost virtual. The spinal accessory nerve crosses the posterior triangle at this level, along with some lymph nodes. At the lower end, both fascial layers further separate, the deep layer covering the scalene muscles, whereas the superficial layer remains attached to the trapezius muscle and the clavicle. The phrenic nerve runs inferiorly on the anterior aspect of the scalene group, covered by this fascial layer. As it proceeds medially, the deep layer attaches to the anterior tubercles of the transverse process of the cervical vertebrae. From here it crosses the midline where it attaches to the transverse process of the cervical vertebrae of the opposite side, passing posterior to the esophagus and anterior to the spine. It is this prevertebral part that gives its name to this fascial layer.
The carotid sheath or vascular sheath lies between the superficial and the prevertebral layers of the deep cervical fascia (Fig. 2-3). It may be regarded as a cylinder-like structure made of fascial laminae connecting the superficial and deep layers. This vascular sheath runs from the base of the skull to the root of the neck. It has independent compartments for the internal jugular vein, the carotid artery, the vagus nerve, and the ansa cervicalis. It attaches to the prevertebral layer at the level of the anterior scalene muscle. The cervical portion of the sympathetic trunk runs posterior to the carotid sheath.
Fascial compartmentalization allows the removal of cervical lymphatic tissue by separating and removing the fascial walls of these "containers" along with their contents from the underlying vascular, glandular, neural, and muscular structures.
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