FINAL DIAGNOSIS: RECURRENT PLEXIFORM FIBROHISIOCYTIC TUMOR
Plexiform Fibrohistiocytic Tumor is a rare mesenchymal neoplasm of low-grade malignancy. This tumor was first described by Enzinger and Zhang in 1988. It has strong female predilection (F: M, 6:1) and occurs almost exclusively in children, adolescents and young adults. The most common locations are the upper extremity especially fingers, hands and wrist followed by the lower extremity. The typical presentation is a small (1-3cm), poorly circumscribed, slowly growing painless mass of the deep dermis and subcutaneous tissues with a gray-white trabecular appearance and a firm consistency.
This tumor is characterized clinically by local recurrence in a third of the cases and rare episodes of regional lymph node metastasis. One case has been reported with pulmonary metastases in a 4-year-old girl.
Histologically, tumor is multinodular and composed of nests of well-differentiated histiocyte-like cells, spindle fibroblast-like and multinucleated osteoclast-like cells in variable proportions and have three distinct growth patterns: fibrohistiocytic (36%), fibroblastic (32%) and mixed (32%), depending on the predominant cell type. The cells within these nodules do not show atypia or significant levels of mitotic activity (<3mitoses/10 high-power fields). The nodules are circumscribed by short fascicles of fibroblastic cells that ramify within the soft tissue creating a plexiform growth pattern.
Immunohistochemically the tumor cells express smooth muscle actin. The rounded cells within the nodules express CD-68.Ultrastructural studies have identified cells with features of histiocytes and myofibroblasts. These tumors frequently recur (40%) within 1-2 years and rarely metastasize to lymph nodes. Pulmonary metastases have rarely been reported.
Contributed by Sassan Rostami, MD and Uma NM Rao, MD