The pathology of head and neck tumors: the occult primary and metastases to the head and neck, Part 10.

Metastases from carcinomas to the head and neck, either to lymph nodes or to extranodal sites, arise most often from known primary neoplasms. However, some are from a clinically inapparent neoplasm--the so-called occult primary. If the metastasis is an epidermoid carcinoma in a lymph node, the odds clearly favor the primary being in the upper aerodigestive tract. The success rate of discovery is variable, however, and a significant number of primaries remain undetected. Metastatic adenocarcinomas, to either nodal or extranodal sites, are most often from infraclavicular neoplasms. In general, the incidence of metastases to the head and neck from visceral primaries below the clavicle follows the general incidence of the primary cancer itself. Renal-cell carcinoma is the exception since its frequency of metastases to the head and neck exceeds the expected incidence in the general population. Branchiogenic carcinoma is more a conceptual than a literal clinicopathologic entity. The diagnosis should be made with reluctance and only after fulfillment of several rather stringent criteria.