END as a management strategy for the N0 neck has evolved because the status of the cervical lymphatics is the single most important prognostic factor in HNSCC. A subset of patients without clinical evidence of regional metastases are known to harbor occult metastases. Despite intensive research efforts to identify pathologic and molecular tumor markers that reliably predict the presence of occult cervical metastases, accurate biomarkers have not been characterized. Although tumor thickness,1, 2 perineural invasion,³ lymphocytic infiltration,⁴ and molecular tumor markers⁵ are associated with occult metastases, they do not provide the accuracy required for therapeutic decision making. Examination of the neck contents after END provides pathologic staging and prognostic information, and accurately guides treatment decisions.

Definition of the NO Neck

Clinical staging of the neck consists of physical examination and includes the results of imaging studies.⁶ Computed tomography (CT) and magnetic resonance imaging (MRI) are commonly employed to evaluate the neck and can be helpful in patients whose necks are difficult to examine by palpation. The radiographic criteria that designate a lymph node as suspicious for metastases include size >1.0–1.5 cm, spherical shape, evidence of necrosis or soft tissue invasion, and groups of three or more nodes.^{7, 8}

Studies that have corroborated CT findings and pathologic staging data from N0 patients now question the accuracy of radiographic staging. An estimated 50% of cervical metastases are <5.0 mm.⁹ Because micrometastases do not meet the size criteria, they are not considered suspicious on CT. Radiographic staging of the submandibular region in particular may be less accurate than physical examination because most (85%) level I metastases are <1.0 cm.^{10, 11} CT staging of the neck misses at least one-third of occult cervical metastases.^{12, 13} The sensitivity of CT staging is estimated to be 25%, and the specificity 77%.¹⁴ Therefore, pathologic staging is the most accurate tool available to assess the status of the cervical lymphatics.

Alternatives for Therapy

An assessment of the risk of occult regional metastases is based on the site, stage, and pathologic characteristics of the primary tumor. Management of the N0 neck is typically addressed when this risk is estimated to be >20%.^{15, 16} With the exception of early-stage glottic tumors and very small superficial lesions, most primary tumors of the upper aerodigestive tract staged N0 probably warrant consideration of the neck.

Three management options exist for N0 patients who are determined to be at significant risk of occult metastases. A program of clinical observation reserves neck dissection for patients who develop regional metastases subsequent to treatment of the primary tumor. Elective neck irradiation (ENI) delivers a tumoricidal dose of radiation to the cervical lymphatics. END is the third option.

The salvage rate for patients who develop regional metastases during a program of clinical observation is estimated to be 50 to 59% after multimodal therapy.^16–18 Although a subset of truly pN0 managed with observation will not receive unnecessary surgery, those in whom cervical metastases do develop will have a poor outcome.

If the decision is to treat the N0 neck, radiation and surgery are options. For patients whose primary tumor is treated with irradiation, ENI is probably the treatment of choice. If the primary is treated surgically, one must decide whether to dissect or to radiate the neck.

As the regional recurrence rates after treatment of clinically N0 patients are 2.0 to 8.0% for ENI^{19, 20} and 2.0 to 11.0% for END,^21–24 other considerations are factored into the choice of treatment. Important differences include the length of time required for treatment, the comparative cost of treatments, and the increased morbidity associated with postirradiation surgery, if required.

If the primary tumor is resected, a policy of ENI will expose 60 to 70% of patients to the sequelae of irradiation unnecessarily. Radiation is not a benign form of therapy. Possible effects include xerostomia, fibrosis, and contracture, which confound the physical examination. Atherosclerosis and radiation-induced malignancy are also reported.^{25, 26} Patients who receive ENI will not get the prognostic information afforded by pathologic staging, and cervical irradiation will not be an option for recurrent or second primary disease.

The morbidity of neck dissection is an important factor in considering END. Compared with radical neck dissection, the routine use of selective procedures has decreased the impact of END on postoperative appearance and function. The main determinant of cost for END is surgical time; hospital stays are generally not lengthened if the primary tumor is resected.

An estimate of the incidence of occult cervical metastases is available by reviewing studies that have reported the regional metastatic rate in patients who were observed clinically. Patients who develop cervical metastases subsequent to treatment of their primary tumor, and who have their primary site controlled, can be assumed to have had occult disease at the time of diagnosis. Table 1-1 presents the data reported for oral cavity lesions and suggests that the occult metastatic rate is 40 to 50%.^{17, 18, 27, 28}

Another way to assess the incidence of occult metastases is to review studies that have reported pathologic staging data on patients whose necks were dissected electively. Data from three studies^{23, 24, 29} are shown in Table 1-2

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