Test and teach. Number 67. Palisaded myofibroblastoma. (Intranodal hemorrhagic spindle cell tumor with "amianthoid" fibres)

Intranodal palisaded myofibroblastoma

Intranodal palisaded myofibroblastoma (IPM) usually presents as a painless, slow-growing inguinal mass. Our review of 42 cases from 13 publications indicates that two thirds of IPMs occur between the ages of 45 and 55 years, the male-female ratio is 2:1, and there is a lack of ethnic predilection. Grossly, the IPM cut surface shows areas of hemorrhage. Five microscopic features are seen: (a) compressed remnants of lymphoid tissue at the periphery; (b) spindle cells with nuclear palisading; (c) intraparenchymal hemorrhage and erythrocyte extravasation; (d) so-called amianthoid fibers; and (e) intracellular and extracellular fuchsinophilic bodies that stain positive for smooth muscle actin. Immunohistochemically, IPM is positive for smooth muscle actin and cyclin D1 and negative for S100, glial fibrillary acidic protein, CD34, and desmin, and it shows a low proliferative index of Ki-67. Electron microscopy demonstrates features of myofibroblasts and smooth muscle cells. Excellent prognosis is seen after surgical treatment, with an approximately 6% recurrence rate and no malignant transformation.

Recurrent intranodal palisaded myofibroblastoma with metaplastic bone formation

Intranodal palisaded myofibroblastoma (IPM) is a rare primary nonlymphoid tumor of the lymph node, which can easily be mistaken for other spindle cell tumors. Intranodal palisaded myofibroblastoma is thought to arise from intranodal myofibroblasts, a finding that is supported by its immunophenotype, positive immunostaining for actin and vimentin, and negative immunostaining for desmin. Characterized by a benign clinical course, IPM is treated by simple surgical excision. We describe a 49-year-woman, who had cadaveric renal transplantation in 1992 and recurrent IPM 41/2 years after its original excision. To our knowledge, this case represents only the second known case of recurrent IPM. The histologic feature of metaplastic bone formation in this case has not been previously described in IPM.

Intranodal palisaded myofibroblastoma with so-called amianthoid fibers: a report of two cases with a review of the literature

Two cases of intranodal myofibroblastoma, a rare primary spindle cell tumor of the lymph node, are described. The tumors arose in the inguinal or proximal region of the thigh of one middle-aged and one elderly Japanese male. The tumors were well-demarcated and composed of a fascicular proliferation of spindle cells with focal nuclear palisading and acellular stellate-shaped collagen-rich areas (so-called amianthoid fibers), and were associated with hemorrhagic areas. Immunohistochemically, the tumor cells were positive for vimentin and muscle actin. Together with ultrastructural findings of intracytoplasmic microfilaments with focal densities and profiles of well-developed, rough endoplasmic reticulum, these features reinforced the conclusion of myofibroblastic or smooth muscle differentiation of the tumor cells. One of the tumors was analyzed by flow cytometry and was shown to be DNA diploid. The present report provides clinicopathological findings of the first two Japanese cases of intranodal myofibroblastoma.