Synovial metastasis: diagnosis by fine-needle aspiration cytologic investigation.

Synovial metastases are a rare occurrence. Only 28 cases have been reported in the literature, 10 of which were diagnosed by fluid cytologic evaluation. We discuss 2 additional cases in which the diagnosis was made by fine-needle aspiration cytologic investigation. The first case is of a 47-yr-old man with small-cell carcinoma of the lung metastatic to the right knee joint; the second is of a 71-yr-old man with non-Hodgkin's mixed-cell nodular lymphoma also involving the right knee joint. The clinical features of these cases are similar to previously published instances of secondary synovial tumor, namely in regard to sex distribution (14 male and 16 female patients), age range (13-96 yr, mean 59 yr), and histologic types (adenocarcinoma, 13 cases; squamous-cell carcinoma, 4; lymphoma, 3; renal clear-cell carcinoma, 3; unknown origin, 2; rhabdomyosarcoma, 1; melanoma, 1; chordoma, 1; pulmonary clear-cell carcinoma, 1; and Ewing's sarcoma, 1). The condition usually has poor prognosis, with average patient survival of < 5 mo.