Urethral caruncle with atypical stromal cells simulating lymphoma or sarcoma--a distinctive pseudoneoplastic lesion of females. A report of six cases.

Six urethral caruncles in women aged 32 to 82 (average, 56) years contained atypical stromal cells raising concern for a neoplasm. The atypical cells varied from spindled to round, the latter predominating, and typically had scant cytoplasm. A minority of the cells were binucleated or multinucleated and often had prominent nucleoli. A single mitotic figure was found in the atypical cells in one case. The atypical cells were characteristically present in an edematous background containing numerous inflammatory cells and were focally crowded together in five cases. The differential diagnosis in these cases included a florid reactive proliferation of lymphoid cells, but immunohistochemical stains failed to support a lymphoid nature for the atypical cells and also helped to exclude malignant lymphoma, the neoplasm most often simulated. Because of the invariable additional component of atypical spindle cells resembling those described in the stroma of the lower female genital tract and in polyps in a variety of sites, the round cells likely represent a variant of this atypical mesenchymal cell. Similar round mesenchymal cells have also been documented in the gastrointestinal tract, especially the stomach. Immunohistochemical stains in this series showed them to be positive for vimentin in four of four cases and for alpha smooth-muscle actin in two of four cases. The prominence of atypical round stromal cells in these cases appears to be a distinctive feature of some urethral caruncles. The presence of these cells should not lead to misinterpretation of the lesion as a neoplastic process.