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Psammomatous Melanotic Schwannoma

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Psammomatous melanotic schwannoma (PMS) consisting of Schwann cell-like spindled and polygonal cells arranged in intersecting fascicles and syncytial sheets. The nuclei are hyperchromatic and some show prominent nucleoli. The nuclear detail may be obscured by heavy melanin pigmentation which can be coarsely clumped or finely granular.

Differential diagnosis: PMS should be distinguished from metastatic malignant melanoma. Features favoring PMS include lack of significant nuclear atypia or increased mitotic activity, predominantly spindled morphology, heavy pigmentation, and psammoma bodies.

Prognosis: The behavior of PMS is difficult to predict from histologic features. A recurrence rate of 32% and a metastates rate ranging from 13% to 44% has been reported, therefore all cases should be considered potentially malignant. The greatest risk of metastasis is in tumors with >2 mitoses/10 HPF. Long-term follow-up is required to fully assess the biologic behavior.

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