Written by Javier Gavilán (jgavilan@coagavilan.es)
Metastatic neck disease is recognised as a prominent factor determining patients’ prognosis with head and neck cancer. Laryngeal tumors are associated with a significant incidence of occult regional metastasis. In fact, up to 30% of the patients with supraglottic tumors may develop nonpalpable neck nodes. Furthermore, a significant number of these patients develop bilateral neck metastasis. With these facts in mind it is obvious that neck treatment must be considered in laryngeal cancer patients even in the absence of palpable nodal disease.
In 1906 George Crile systematized the en-bloc removal of the lymphatic tissue of the neck. This operation – named Radical Neck Dissection – included in the resection the sternocleidomastoid muscle, the internal jugular vein, the submandibular gland and the spinal accessory nerve.
This is still the most adequate surgical approach for patients with large clinically proven neck disease. However, for the clinically N0 patient, Radical Neck Dissection is too aggressive. Likewise, in patients who may develop bilateral occult regional disease, this operation is impractical due to its complications, morbidity and potential mortality. Bilateral simultaneous Radical Neck Dissection is a risky procedure. It may be justified in patients with advanced neck disease, but it should not be considered for N0 patients.
Unlike Anglo-Saxon countries, where the glottis is the main location of laryngeal cancer, in Latin countries supraglottic tumors comprise the majority of laryngeal tumors. It is well known that supraglottic cancers are highly metastatic and they may metastasise to both sides of the neck. For these patients we need a surgical approach as effective as Radical Neck Dissection but less aggressive with the patient.
In the mid ’60s Osvaldo Suárez, an Argentinian otolaryngologist, proposed a new approach to neck dissection based on fascial compartmentalisation of the neck. Employing fascial planes as a concept to perform excision of neck nodes is based on specific anatomic concepts regarding the relationship between the lymphatic structures and the distribution within the tissues of the neck. This concept, scarcely published in Spanish, allows the removal of the lymphatic tissue of the neck, preserving the major non-lymphatic structures.
The basic understanding of the fascial planes in the neck is that there are two distinct layers, the superficial cervical fascia, and the deep cervical fascia.
The superficial fascia is a connective tissue layer lying just below the dermis. Surgically it is indistinct from the fatty tissue that surrounds it. In the neck is one of the few places where it splits to surround the muscles of facial expression. The space deep to this layer contains fat, neurovascular bundles and lymphatics. It does not constitute part of the deep neck space system.
The deep cervical fascia encloses the deep neck spaces and is further divided into 3 layers, the superficial layer, the deep layer and the carotid sheath, lying between the superficial and deep layers.
The superficial layer of the deep cervical fascia arises posteriorly from the vertebral spinous processes and ligamentum nuchae. It surrounds the entire neck, splitting to enclose the trapezius muscle, the omohyoid muscle, parotid gland, sternocleidomastoid muscle and the strap muscles. Anteriorly, this fascia is attached to the hyoid bone. The inferior attachments of the fascia are the acromion of the scapula, the clavicle, and the sternum. The fascia remains split in two layers until it attaches to the sternum; thus, the superficial layer attaches to the anterior surface of the sternum and the posterior layer to the posterior surface of the sternum.
The deep layer of the deep cervical fascia is also called “pre-vertebral fascia” because it makes a prominent layer just in front of the vertebral column. This fascia also arises posteriorly from the transverse and spinous processes of the cervical vertebrae and the ligamentum nuchae. It passes laterally around the prevertebral and postvertebral muscles and covers the scalene muscles anteriorly, then passes in front of the vertebral body and forms a thick layer from which it receives its name. This thick fascial layer forms the floor of the posterior triangle of the neck, and anterior to the vertebral bodies, it provides a base on which the pharynx, oesophagus, and other cervical structures glide during swallowing and neck movements. The cervical and branchial nerve plexus and the sympathetic trunk are invested by the prevertebral fascia. The consequences of elevating the prevertebral fascia during a neck dissection, beyond merely increasing the devastation wrought by the surgical exercise, can be severe. If this fascia is raised, there is risk of involving what lies deep in the fascia, notably the cervical and brachial plexus, the sympathetic trunk, and the phrenic nerve. The cervical plexus emerges from between the scalene muscle bundles. The phrenic nerve crosses obliquely on the anterior surface of the anterior scalene muscle from lateral to medial and lies deep to the prevertebral fascia.
The carotid sheath encloses the vascular axis of the neck (carotid artery and internal jugular vein) as well as the vagus nerve. Each one of these three structures has independent compartments covered by thin fascial projections from the carotid sheath. The sympathetic trunk lies posterior to the carotid sheath and runs in a different plane.
Fascial compartments allow 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. To ensure oncologic safety, Functional Neck Dissection requires that all nodal disease be confined within the lymphatic tissue. The operation fits perfectly for all N0 patients with high-risk of occult metastasis, like oral cavity, oropharynx, and supraglottis. It can be performed simultaneously on both sides of the neck without increasing morbidity. This procedure may also be used in patients with small nodes (<2.5 cm) not invading the surrounding fascia.
The oncologic results of Functional Neck Dissection are comparable to those of the classic operation as long as its indications are carefully followed. Simultaneous bilateral Functional Neck Dissection is associated with a significant decrease of neck failures in patients with supraglottic tumors.
This operation should be considered the ideal surgical procedure for patients under high-risk of occult unilateral or bilateral neck metastasis, as well as for those with small mobile nodes.