Solitary spindle cell tumor with myoid differentiation of the lymph node.

Spindle cell tumors arising in the lymph nodes are very rare. We report the light microscopic, histochemical, immunohistochemical, and ultrastructural findings of an unusual solitary spindle cell tumor in a peripheral lymph node of a 45-year-old woman. Microscopically, the tumor was characterized by interlacing fascicles of uniform spindle cells with nuclear palisading and formation of Verocay bodies. Numerous erythrocytes were found interstitially. There were no mitotic figures or significant nuclear atypia. The ultrastructural findings of abundant myofilaments with dense bodies indicated myoid differentiation. The clinical and pathologic findings favored this being a benign tumor and could represent a unique example of "intranodal myofibroblastoma." The differential diagnosis includes neurilemoma, leiomyoma, and, more importantly, leiomyosarcoma, Kaposi's sarcoma, and other metastatic spindle cell tumors.