Intranodal hemorrhagic spindle-cell tumor with "amianthoid" fibers. Report of six cases of a distinctive mesenchymal neoplasm of the inguinal region that simulates Kaposi's sarcoma.

We describe six cases of a distinctive spindle-cell neoplasm apparently arising from inguinal lymph nodes in adult patients. The lesions were characterized histologically by highly vascularized, interlacing fascicles of spindle cells circumscribed by an irregular band of sclerosis and hemorrhage, and surrounded by a compressed rim of lymph node remnant. A striking feature observed in all cases was the presence of stellate-shaped areas containing thick collagen fibers (so-called amianthoid fibers). Immunohistochemically, the tumor cells were positive for actin, muscle myosin, and vimentin. Electron-microscopic examination demonstrated features indicative of myofibroblastic and smooth-muscle differentiation. Follow-up has shown no evidence of recurrence or metastases. The lesions appear to represent an intranodal neoplastic proliferation of mesenchymal cells exhibiting benign biologic behavior. The inguinal location, presence of amianthoid fibers, and the striking rim of hemorrhage surrounding the spindle-cell proliferation set this tumor apart from other lesions. It is important to distinguish this entity from nodal involvement by Kaposi's sarcoma, a lesion it may closely resemble.