By Dale R. Ehmer Jr., MD
Surgical dissection of the neck as part of treatment and diagnosis of head and neck malignancy was brought to the medical literature in 1907 by Crile. He coined the term, the ‘en-bloc cervical lymphadenectomy’, which we would consider today to be the radical neck dissection. While there have been many advances and alternate forms of therapy, the Crile radical neck dissection is still performed today. Modifications have been made to the surgical technique, yet the basic facts of anatomic structures and their relationships to other structures forms the basis of the surgical knowledge necessary to navigate this complex area.
Anatomy:
Knowledge of the anatomy of the neck is an essential quality of the head and neck surgeon. The vascular supply to the skin arises from the superficial plexus of blood vessels that course vertically in the neck, pierces the platysma, and branches out to the skin structures. The major blood vessels contributing from the superior neck include the facial, submental, and occipital arteries, and the blood vessels contributing from the inferior neck include the transverse cervical and subscapular. The source of the blood makes incision planning important, especially when performing a radical neck dissection. The majority of neck incisions have transverse and vertical portions, with the transverse portions either in the upper, middle or lower third, and the vertical portions overlying the sternocleidomastoid muscle. Those incisions that have a trifurcation should be placed so that the intersection of the incisions does not form a too acute angle nor should it overly the carotid artery in case of wound dehiscence.
The first muscle encountered in neck surgery is the platysma muscle, which is quadrangular in shape (dehiscent in the midline and posterolaterally), innervated by the facial nerve, and is contiguous with the superficial musculoaponeurotic system (SMAS), which is contiguous with the temporoparietal fascia (TP fascia). Dissection is performed in the subplatysmal plane. Once the dissection is carried superiorly to the mandible and inferiorly to the clavicle, the neck is completely exposed. The SCM is identified as fibers running perpendicular to those of the platysma. Lateral to the SCM but medial to the platysma are the external jugular vein (EJV) and the great auricular nerve. The great auricular nerve arises from posterior to the SCM at Erb’s point (6-6.5 cm inferior to the mastoid tip), courses superiorly and posteriorly to supply sensory innervation to the external ear. On the posterior surface of the SCM at a point 1-2cm superior to Erb’s point will be the posterior neck portion of the CN XI. Sharp dissection through the investing fascia of the submandibular gland at the inferior aspect of the gland and reflection of the fascia superiorly will protect the marginal mandibular branch of the facial nerve. Once the facial vein is identified and ligated, one knows that the nerve is lateral and therefore safe. Identifying the anterior belly of the digastric in the submental triangle will lead to the identification of the posterior belly of the digastric from the common tendon on the superior edge of the hyoid bone. Following the digastric muscle posteriorly will protect the vital deep neck structures. The facial artery, however, loops over the superior aspect of the posterior digastric just anterior to the retromandibular vein, and these structures need to be watched for as one dissects posteriorly along the digastric. On the floor of the submandibular triangle sits the hypoglossal nerve along with its associated veins. It loops around the occipital artery and passes deep to the mylohyoid but superficial to the hyoglossus on its course to the tongue musculature. CN XII is in very close proximity to the lateral, superior aspect of the hyoid bone. Identifying the CN XI in the anterior neck can be done by dissecting along the SCM superiorly until the tendonous portion is identified. CN XI is usually no more than a few millimeters superior to the tendon of the SCM on the medial side. Tracing the CN XI superiorly one will find the IJV medially 70% of the time. In the posterior neck, CN XI stays superficial, and is on the medial aspect of the trapezius muscle, yet it can be easily injured during posterior neck operations. The omohyoid muscle separates the inferior neck (level IV) from the middle neck (level III), and it protects the great vessels in the inferior neck. The thoracic duct carries lymphatic drainage to the central circulation and it can be found posterior and medial to the IJV in the deep inferior neck. Deep to the great vessels and deep to the deep cervical fascia runs the brachial plexus, phrenic nerve, sympathetic chain ganglion, and the deep cervical motor nerves. These structures should not be encountered on a routine neck dissection.
Lymph Node Groups
In the head and neck region are an estimated 200-250 lymph nodes. These are grouped by anatomic location into 6 large groups. Three of the 6 groups are subdivided into 2 groups, yielding 9 lymph node groups. These roughly correspond to the triangles of the neck. Level IA consists of lymph nodes in the submental triangle. Boundaries for this area are the midline medially, the anterior belly of the digastric muscle laterally, the mandible superiorly or anteriorly, and the hyoid bone inferiorly or posteriorly. Level IB consists of lymph nodes in the submandibular triangle. Boundaries for this area are the mandible superiorly, the anterior belly of the digastric muscle anteriorly, the posterior belly of the digastric muscle inferiorly or laterally, and the stylohyoid muscle posteriorly. This level also contains the submandibular gland. Level IIA consists of lymph nodes in the jugulodigastric region. Anteriorly, this is bordered by the stylohyoid muscle, superiorly this is bordered by the skull base, posteriorly this is bordered by the vertical plane of CN XI, and inferiorly this is bordered by the level of the hyoid bone or the bifurcation of the common carotid artery. Level IIB lies posterior to the level IIA, basically including those lymph nodes posterior to CN XI, medial to the SCM, inferior to the skull base, and superior to the horizontal plane of the hyoid or the bifurcation of the common carotid artery. Level III consists of nodes inferior to the level of the hyoid or bifurcation of the common carotid artery, superior to the omohyoid muscle or cricoid cartilage, lateral to the sternohyoid muscle, and medial to the SCM and deep cervical rootlets. Level IV consists of nodes inferior to the omohyoid muscle, lateral to the sternohyoid muscle, medial to the SCM and cervical rootlets, and superior to the clavicle. Level VA consists of lymph nodes posterior to the SCM, anterior to the trapezius muscle, superior to the omohyoid muscle, and inferior to the skull base. Level VB consists of lymph nodes inferior to level VA, inferior to the omohyoid, superior to the clavicle, posterior to the SCM, and anterior to the trapezius muscle. Level VI consists of the lymph nodes in the anterior triangle. This is bordered by the midline medially, the hyoid superiorly, the clavicle inferiorly, and the sternohyoid laterally. The Delphian node is in level VI.
Staging of Neck Disease by the AJCC
Cervical lymph node metastasis forms the ‘N’ component of the TNM staging system of the AJCC for head and neck cancer sites. Depending on size of lymph node involvement, unilaterality or bilaterality of lymph node involvement, and numbers of lymph nodes involved, staging will be altered. Staging the neck as Nx indicates that the neck disease is not able to be characterized. Staging N0 (zero) indicates no cervical lymph node metastasis. For head and neck malignancies EXCEPT nasopharyngeal cancer, thyroid cancer, and melanoma, the following criteria exist. Staging the neck N1 indicates the presence of cervical metastasis in only one lymph node in the neck, and the size of that lymph node is less than 3cm in size. Staging the neck N2a indicates the presence of cervical metastasis in only one lymph node in the neck, and the size of that lymph node is more than 3cm but less than 6cm in greatest dimension. Staging the neck N2b indicates the presence of cervical metastasis in multiple ipsilateral lymph nodes, none of which are larger than 6cm in greatest dimension. Staging the neck N2c indicates the presence of cervical metastasis in bilateral or contralateral lymph nodes, none of which are larger than 6cm in greatest dimension. Staging the neck N3 indicates presence of any lymph node in the neck larger than 6cm in greatest dimension. Although the traits/size of the primary tumor can upstage the tumor, a good rule is that the presence of N1 or N2 neck disease will be AT LEAST a Stage III tumor. The presence of N3 neck disease will be AT LEAST a Stage IV tumor. This will be important for prognosis of the patient.
Detection of Cervical Lymph Node Metastasis
Upon presentation, the quickest and easiest way to examine the neck is with physical examination. Palpation of the neck carries a sensitivity of slightly more than 70% in finding cervical lymph node metastasis. As part of a metastatic workup, however, imaging studies are performed. For our clinical practice, a CT scan of the neck with IV contrast enhancement is performed. If lymph nodes are larger than 1cm in the neck, except in the jugulodigastric region where they need to be greater than 1.5cm, they are considered to be cervical lymph node metastasis. Other characteristics of the node, such as rim enhancement, central necrosis, round shape, or peripheral thickening can also increase suspicion of cervical metastasis. By itself, CT scan with contrast carries about an 83% sensitivity and specificity, but when it is combined with physical exam, the sensitivity increases to >90%. Other imaging studies, such as MRI with gadolinium, PET/CT, or high-resolution ultrasound are also used with roughly equivalent sensitivities and specificities. Detection of cervical metastasis after radiation therapy with or without chemotherapy becomes more difficult. At this time, having performed a baseline PET scan can be very helpful, for a follow-up scan can show elimination of uptake in the concerning area which can argue for resolution of disease. A recent study showed that the negative predictive value of physical exam, CT neck, and PET scan (when all 3 were negative) was 100%.
Surgical Treatments
Crile described the en bloc cervical lymphadenectomy in 1906 for treatment of neck metastasis from upper aerodigestive carcinomas. This has been re-named the radical neck dissection. Although there was controversy regarding performing this extent of surgery for minor neck disease over the next 60 years, Bocca published his work on the functional neck dissection in 1967. This functional neck dissection, also known now as the type III modified radical neck dissection removed all lymph node bearing tissue but spared the IJV, CN XI, and SCM resulting in better function after neck surgery. In 1986, Byers and Medina, utilizing the work of Lindberg, defined the selective neck dissection to further narrow the field of lymph node excision to those areas known to drain from various primary tumor sites.
The radical neck dissection involves excision of all lymph node bearing tissue in the neck (levels I-V), the SCM, the IJV, and the CN XI. This results in decreased shoulder mobility and poor cosmetic appearance. By modifying the radical neck dissection to spare the CN XI, one performs a Type I MRND. Sparing the CN XI and IJV, one performs a Type II MRND, and sparing the CN XI, IJV, and SCM, one performs a Type III MRND (functional neck dissection).
The selective neck dissection selects subsets of lymph node groups for excision based upon the drainage pattern of the primary tumor. These are now classified as selective neck dissection (SND) and the lymph node groups removed. For example, removing lymph node groups I, II, and III would be SND (I-III). The SND (I-III) is also known as the supraomohyoid neck dissection and is used for primary tumors of the oral cavity: floor of mouth, alveolar ridge, and tongue. If the tongue is the primary, then SND (I-IV) is performed. The SND (II-IV) is also known as the lateral neck dissection and is used for primaries of the oropharynx, larynx, hypopharynx, and pharyngeal wall. The SND (VI) is also known as the anterior neck dissection and is used for primary tumors of the thyroid gland. If the cervical lymph node metastasis is in more than 1 lymph node or there is extracapsular spread of tumor, post-operative XRT is indicated.
The extended neck dissection is the most extensive neck dissection surgery performed today. The field of resection includes all parts of the radical neck dissection but a carotid artery resection and possible resection of the deep cervical fascia structures is included.
Complications of Neck Dissection
Post-operative or intra-operative complications of the neck dissection often have dire consequences. Carotid artery rupture, air embolism, salivary fistula, hematoma, blindness, coma, nerve paralysis, and chyle leak are just some of them. Air embolism occurs when a large caliber vein is opened to the outside world and the negative pressure in the venous system draws air into the vessel. Approximately 100cc of air is necessary to be hemodynamically significant. Immediate treatment is required which includes placing the patient in the Trendelenburg position (head below feet) and in the left lateral decubitus position. This places the right ventricle of the heart up, effectively trapping the air embolus before it can get to the pulmonary system. The embolus can then be withdrawn by a syringe directly into the right ventricle.
A chyle fistula occurs when a lymphatic duct, most commonly the thoracic duct, is cut and not ligated. The incidence of chyle fistula is about 2%, and it is diagnosed intraoperatively by an oily liquid pooling in level IV which increases with Valsalva maneuver. Post-operatively it is diagnosed with a possibly high drain output with a triglyceride level > 100mg/dL. The output is usually cloudy in nature. The leak can occur immediately postop or can be delayed and onset with initiation of enteral feeds. If the leak is diagnosed within the first 24 hours postop or has a high output (> 600cc/day), surgical intervention is preferred for management. This is due to the inflammatory process that occurs with the tissue reaction to chyle that makes identification difficult and the low likelihood of conservative management success. Conservative management consists of bedside aspiration, pressure dressing, dietary change to a medium chain fatty acid diet, and possible TPN. By changing to the MCFA diet, the portal system absorbs all of the fatty acids and the thoracic duct does not transport fatty acids to the circulation. Intraoperative management consists of prophylactic measures first, specifically clamping the inferior aspect of the neck dissection specimen with a large clamp and tying a permanent suture ligature to seal off any potential lymphatic vessels. Once a chyle leak is confirmed intraoperatively, hemoclips are useful to ligate the offending duct as is tying a suture ligature over a hemostatic sponge to prevent avulsion of the fragile tissue. Whether or not a chyle leak is suspected, performing a Valsalva maneuver prior to closure in a bloodless field is indicated.
Increases in intracranial pressure (ICP) after bilateral neck dissection, especially with bilateral IJV ligation, can occur. Early neurological changes associated with increased ICP such as lethargy, nausea, or difficulty in arousal can herald a vicious cycle that can have severe consequences. Ligating the outflow of blood from the brain can lead to venous congestion which increases ICP, but the brain may initiate ADH secretion inappropriately (SIADH) which leads to expansion of blood volume and hyponatremia. This further increases ICP and ADH release which furthers the problem. Close ICU monitoring with CVP, ICP, urine studies, electrolytes, and urine osmolality along with mannitol, hyperventilation, and free water restriction treatment may be necessary.
Management of the N0 Neck
Much controversy exists regarding management of the N0 neck. The rule of 20% can be applied and has been agreed upon by most head and neck surgeons as an acceptable theory to dictate intervention. Basically, if the primary site has a 20% or higher chance of leading to occult cervical metastasis (N0 neck), elective treatment of the neck should be undertaken. Oral cavity tumors, specifically those that involve the tongue (any T), floor of mouth (any T), lip (T3, T4 not at commissure), or retromolar trigone (T2 or greater) should have the necks electively treated. An SND (I-III) unilaterally should be performed except for tongue primary tumors where level IV should be added. Midline lesions, anterior tongue, or lip commissure primary tumors need bilateral neck dissections. Oropharynx tumors, due to rich lymphatic drainage, usually require bilateral neck treatments. T1 and T2 tonsil cancer neck treatment is controversial. Some argue for bilateral intervention, some argue for unilateral intervention, and some argue for no intervention (T1 tonsil only). Usually, first-line treatment for the primary tumors of the oropharynx is non-operative with chemotherapy and radiation. Laryngeal tumors have vastly different metastatic potential with tumors of the supraglottis and subglottis having very high rates of occult cervical metastasis whereas glottic tumors have very low rates of occult metastasis. This is due to the paucity of lymphatics at the level of the glottis. An important distinction exists for advanced glottic carcinoma with anterior commissure involvement and pre-epiglottic space invasion, though. Tumors in this area require bilateral neck treatment. SND (II-IV, V?) bilaterally is indicated for supra- and subglottic tumors, with level VI indicated for advanced subglottic tumors. Hypopharyngeal tumors also carry a high occult metastatic rate and have rich lymphatic drainage which dictates bilateral neck treatment. Similar to the oropharyngeal primary tumors, first-line therapy is usually chemotherapy and radiation therapy. Nasopharyngeal cancer with or without cervical metastasis is treated with radiation therapy as first line modality, with addition of chemotherapy where indicated by subtype.
Unknown primary
The unknown primary neck mass, defined as cervical metastasis in the absence of known primary tumor origin, occurs in 5-30% of cervical metastasis seen by head and neck surgeons. Workup for the primary tumor localization includes thorough history and physical exam, imaging studies, and possibly panendoscopy with directed biopsies combined with ipsilateral tonsillectomy. Imaging studies include CT and or PET/CT or MRI. The utility of a PET scan in identifying an unknown primary has been reported extensively in the literature. The surgeon must decide whether a PET scan will be used because if a panendoscopy with directed biopsies from high yield sites (naso-, hypo-, oro-pharynx, base of tongue, tonsil fossa) and ipsilateral tonsillectomy is performed, a PET scan cannot be done for 6 weeks due to false-positive uptake in the biopsy sites. Treatment for unknown primary neck disease can include neck dissection and post-operative wide-field radiation or combined chemoradiation.
