Dermatopathology

Pilar Leiomyoma

Pilar leiomyomas are benign circumscribed tumors composed of intersecting fascicles and bundles of smooth muscle. Tumor nuclei are elongated and blunt-ended or "boxcar" shaped. The cytoplasm is eosinophilic. Mitoses are scarce or absent.

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Slide 1: 40 year-old woman with a knee lesion. <br>The resection specimen reveals a dermal based proliferation.

Slide 2: The dermis contains solid areas with short, intersecting fascicles of bland spindled cells with eosinophilic cytoplasm.

Slide 3: The spindle cells have box-car (or pill shaped) blunt ended nuclei.<br><br>No mitotic activity is appreciated.

Slide 4: Immunohistochemistry reveals the tumor cells to express desmin.

Slide 5: SMA is strongly positive as well. There is no staining for S100 or factor XIIIa.