Origins of adenocarcinomas presenting as intracranial metastases. An ultrastructural study.

Adenocarcinomas of unknown origin are a common neurosurgical problem. In many such cases, the primary tumor remains clinically obscure. A series of 28 adenocarcinomas of unknown origin, presenting as intracranial metastases and examined with electron microscopy, was reviewed blindly in a "retrospective prospective" fashion. Distinguishing ultrastructural features allowed prediction of site of origin in 26 cases (93%). Clinical and postmortem follow-up allowed the identification of likely primary tumor sites in 13 cases, with confirmation of the ultrastructural diagnosis in all 13 cases. The great majority of adenocarcinomas of unknown origin were found to originate in the lung (22/26 [85%]), while a few originated in the colon (2/26 [8%]) or kidney (2/26 [8%]). The predominance of pulmonary tumors among intracranial metastatic adenocarcinomas of unknown origin is much greater than the reported 45% to 55% predominance of pulmonary tumors among all intracranial metastatic carcinomas of unknown origin. Electron microscopy is a useful technique to either confirm a bronchogenic origin or to suggest an alternative primary site for these tumors.