Hyperpigmented patch on the trunk of a neonate. Congenital smooth muscle hamartoma (CSMH) or congenital arrector pili hamartoma.

Received: September, 2004. Accepted: December, 2004. Source of Support: Nil. Figure 3: Photomicrograph (Masson Trichrome stain, x40) Figure 1: Hyperpigmented patch on the trunk Figure 2: Photomicrograph (H/E, x4) A one-day-old, full-term, normally delivered, female neonate was being routinely examined. A brownish irregular patch of 2 cm × 1.5 cm, with fine long hairs was observed on her right loin [Figure 1]. On gentle stroking, the lesion became more prominent along with the appearance of goose bumps. A punch biopsy was taken from the edge of the lesion. Histopathological preparation on H/E stain showed mild hyperkeratosis of the epidermis and basal cell hyperpigmentation. In the reticular dermis, well-defined smooth muscle fiber bundles were seen, interspersed among hair follicles [Figure 2]. Masson Trichrome stain [Figure 3] confirmed the presence of smooth muscle fibers (stained red).