Low-grade malignant perineurioma of the paravertebral column, transforminginto a high-grade malignancy

A demarcated 6 x 5 cm right paravertebral tumor at the revel of T6 in a 39- year-old male was removed surgically. Histologically, the tumor consisted o f monomorphous benign-looking, low-cellular spindle cells embedded in desmo plastic stroma. Ten years later, the tumor recurred locally with metastasis to systemic organs, including the occipital skin. Malignancy was histologi cally evident by the increased cellularity, cellular atypia and mitotic act ivity. The patient died of respiratory failure at the age of 49. Retrospect ively reviewed, the primary lesion was low-grade fibrosarcoma-like spindle cell tumor, with secondary transformation into a highly malignant form The differential diagnoses included sclerosing epithelioid fibrosarcoma, low-gr ade fibromyxoid sarcoma and malignant peripheral nerve sheath tumor. Immuno histochemically, the spindle cells in the primary and recurrent tumors cons istently expressed epithelial membrane antigen, vimentin, type 4 collagen a nd laminin. The tumor cells in the present case showed a differentiation to ward perineurial cells, which are normally positive for these immunohistoch emical markers. Hence, the appropriate diagnostic term should be 'malignant perineurioma', a subtype of malignant peripheral nerve sheath tumor.