Abstract
We report a case of malignant myopericytoma that presented in a 58-year-old female with a scalp lesion of unknown duration. The clinical differential diagnosis included epidermoid cyst and lipoma. The histologic sections showed a proliferation of spindled cells with eosinophilic cytoplasm arrange in fascicles and concentrically around thin-walled vessels that in areas had a staghorn pattern. There were scattered pleomorphic cells and numerous mitotic figures (>10/10 HPF), including atypical forms. By immunohistochemistry the tumor was positive for SMA and negative for CD34, desmin, and S100 protein. A diagnosis of malignant myopericytoma was made. This is an extremely soft tissue tumor with relatively few case reported in the literature. Reported cases have shown the propensity for aggressive behavior with a significant risk of metastasis. Histopathologic features associated with malignancy include high cellularity, pleomorphism, high mitotic rate, necrosis, and lymphovascular or perineural invasion. It is uncertain if cutaneous malignant myopericytomas have the same aggressive behavior as deep soft tissue counterparts. This case is presented to call attention to this rare entity.
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