Current Concepts in Surgical Management of Neck Metastases from Head and Neck Cancer

Indications for Postoperative Irradiation

The decision to use postoperative irradiation in head and neck cancer is based on the initial tumor stage and pathologic findings. Both the primary site and neck must be considered in this regard.

Specific to the neck, postoperative irradiation is indicated for extranodal tumor spread or multiple positive nodes, especially at multiple levels. In addition, irradiation is useful for controlling the opposite, undissected neck when it is at risk and the primary site will need postoperative irradiation.

Management of Neck Metastases From an Unknown Primary

Cervical metastases arise overwhelmingly from upper aerodigestive tract squamous cell carcinoma primary sites, although metastases that appear first in the lower portion of the neck may be of infraclavicular origin. When upper- or middle-third cervical metastases are present without an obvious primary site, we recommend a thorough search for that site, including imaging and endoscopy of the upper aerodigestive tract. If no primary is found, histopathology of the lymph node is almost always obtainable by means of fine-needle aspiration cytology.

It is rarely necessary to perform a cervical node excision for diagnostic purposes. If a node excision is required, or is inadvisably performed, radiation must be the next modality utilized in order to achieve a reasonable rate of regional control [21]. This approach may, however, unduly complicate the management of the patient.

Results of Treatment

Survival rates in head and neck cancer vary widely, due to the large number of primary sites and different primary tumor sizes. However, various factors have been examined relative to their influence on the control of regional metastases by neck dissection. Extranodal spread of tumor, which increases in proportion to lymph node size, has been identified as a very important factor affecting regional control and survival [22-24]. An increased risk of distant metastases and a decrease in survival have been demonstrated with an increasing number of positive lymph nodes, particularly when located in the lower neck [22,25,26].

Regional control rates may also be examined with regard to treatment selection. Regional control rates for negative necks or necks with a single, positive node less than 3 cm managed with any type of neck dissection should be 90% or greater [12]. Several retrospective studies have demonstrated no difference in nodal recurrence rates between modified and radical neck dissections for appropriately selected patients [15,27,28].

Similar control rates (90% or greater) may be obtained with irradiation for N0 or early N1 neck disease [29]. For more advanced nodal disease, control rates are improved with a combination of neck dissection and radiation, as compared with either modality alone [12,30].

The salvage rate for recurrence in a previously dissected or previously irradiated neck is low, ranging from 5% to 40%, and salvage appears to be more likely if irradiation has not been previously employed [30,31].

Surgical Considerations

Prevention of Carotid Artery Rupture

Major vascular complications of neck dissection, especially carotid artery rupture, are often catastrophic. In an isolated neck dissection, carotid rupture is an extremely rare event. Carotid artery exposure occurs almost exclusively after the development of a pharyngocutaneous or orocutaneous fistula. Carotid exposure appears to be much less common after modified radical neck dissection, due to the protection provided by the sternocleidomastoid muscle.

Proper skin flap thickness and the placement of skin incisions away from the carotid bifurcation are helpful in preventing carotid exposure. In addition, the adventitia should be left on the carotid, unless there is a positive node partially fixed to the artery.

Once the outer layer of the carotid is exposed, it desiccates and weakens, most commonly at the level of the carotid bifurcation. Full-thickness destruction occurs within approximately 1 to 2 weeks. The first sign of an impending carotid rupture may be a sentinel bleed, which is then usually followed by an actual rupture 24 to 48 hours later. If rupture occurs, the common, internal, and external carotid arteries are ligated, and the bifurcation is resected.

Ligation and resection of the carotid artery for rupture have been associated with death rates of 33% to 50% and neurologic sequelae rates of 15% to 25% among survivors [32]. Elective resection for impending rupture is associated with decreased morbidity and mortality when compared with emergent resection. In highly selected cases, balloon occlusion of the carotid may be useful as a temporizing measure and for the prediction of neurologic outcome. However, despite the results of such a test, the artery most often will still require ligation.

Various methods of tissue coverage have been suggested for the prevention of carotid exposure after radical neck dissection; however, the effectiveness of such attempts is not clear [32]. Although dermal grafts are employed most commonly, the use of levator scapulae muscle flaps, omentum, and prevertebral fascia has been described. Dermal grafting is most likely to be of benefit in cases of radical neck dissection that have a possibility of a pharyngocutaneous or orocutaneous fistula and a history of prior irradiation, especially if the carotid adventitia was removed.

Sacrifice of the Internal Carotid Artery

If irradiation has not been successful in freeing a fixed node from the carotid artery, a decision must be made relative to carotid artery resection. Even though carotid artery resection with bypass may result in acceptable perioperative morbidity and mortality [33], we generally do not perform this maneuver, as survival is not improved with carotid artery resection [34,35].

Benefit of Saving the Spinal Accessory Nerve

A variety of neural injuries may be evident after neck dissection, but injuries to the spinal accessory nerve predominate. The spinal accessory nerve passes through the lymph node-bearing tissue of the neck, requiring that it either be sacrificed or dissected for preservation.

The majority of permanent spinal accessory nerve injuries are associated with the purposeful sacrifice of the nerve in conjunction with a radical neck dissection. This results in denervation of the trapezius muscle. The associated "shoulder syndrome" consists of shoulder pain, weakness, impaired mobility in abduction of the arm over 90°, shoulder droop, and scapular winging. The shoulder pain is due to the increased demands for support of the scapula on the levator scapulae and rhomboid muscles, and is worse if the dorsal scapular nerve is also injured. An adhesive capsulitis of the shoulder joint may develop as well, and predominate symptomatically [36].

Because loss of the spinal accessory nerve is generally the most debilitating part of a radical neck dissection, various methods of preserving trapezius function have been utilized. Given that the spinal accessory nerve receives contributions from the second, third, and fourth cervical nerves, preservation of these branches was proposed as a method of preserving some trapezius function. However, it now seems clear that these branches are mostly proprioceptive in nature, and any residual shoulder function was more likely due to preservation of the nerve to the levator scapulae muscle.

Resection of the spinal accessory nerve and cable grafting achieves some diminution of the shoulder syndrome. A "save XI" neck dissection still results in significant atrophy of the trapezius in up to 50% of patients, due to the extensive trauma to the nerve and devascularization associated with this procedure.

Modified radical neck dissection with preservation of the sternocleidomastoid muscle and spinal accessory nerve is associated with the least trauma to and devascularization of the spinal accessory nerve. This ultimately results in the best trapezius function, although there is still a temporary phase of dysfunction, which recovers significantly by 6 months after neck dissection, as documented by electrodiagnostic testing [37]. Since modified radical neck dissection is associated with acceptable nodal recurrence rates, this has become the nerve-sparing procedure of choice.

Benefit of Saving the Internal Jugular Vein

The internal jugular vein is typically conserved in modified radical and selective neck dissections. This allows the performance of simultaneous bilateral neck dissections with a diminished risk of increased intracranial pressure, the syndrome of inappropriate antidiuretic hormone secretion, facial edema, blindness, stroke, and airway obstruction.

The benefit of saving the internal jugular vein during a unilateral neck dissection is not as clear, but logically would seem to be of benefit, to a lesser degree. The internal jugular vein has been demonstrated to be reliably patent following conservation procedures. Factors that are associated with the rare instance of internal jugular vein thrombosis include prior irradiation, nodal recurrence, and compression by a musculocutaneous flap [38-40].

Conclusion

The surgical management of cervical metastases from head and neck cancer has undergone a significant change to more conservative techniques for appropriately selected individuals. Improved imaging modalities facilitate the staging of cervical metastases. The selection of the appropriate treatment for the neck is best done by a multidisciplinary group of surgeons, radiation oncologists, medical oncologists, path- ologists, and radiologists due to the complex relationship between the management of the primary site and the neck.