Abstract

Congenital smooth muscle hamartoma is a rare benign smooth muscle proliferation that usually presents as a single lesion in the lumbosacral area or in the proximal extremities in infants. Clinically it usually presents as a macule, plaque, or perifollicular papule that is often hyperpigmented and hair-bearing. Other less common clinical presentations have been reported including atrophic plaques and micropapillary plaques. Cases presenting clinically as a polypoid tail-like lesion have not been reported in the literature to our knowledge. Herein, we report the first case of a congenital smooth muscle hamartoma presenting as a polypoid lesion. A 4-month-old baby presented with a congenital polypoid lesion on the lumbosacral area measuring 1.5 cm. Clinically, the impression was “rule out vestigial appendage/human tail”. A shave biopsy of the lesion was performed and showed a polypoid mass lined by benign acanthotic epithelium and containing a fibrovascular dermal core. The dermal core also contained a nodular proliferation of bland spindled cells arranged in intersecting fascicles. Immunohistochemical stains were performed. The spindle cells demonstrated strong and diffuse staining of desmin and alpha-smooth muscle actin (ASMA), supporting a diagnosis of congenital smooth muscle hamartoma. In conclusion, this case illustrates a rare and previously unreported polypoid variant of congenital smooth muscle hamartoma.

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