Nevus psiloliparus: Newly described histopathological features from transverse sections.

Nevus psiloliparus is a rare fatty tissue nevus that is a marker for encephalocraniocutaneous lipomatosis, a neurocutaneous syndrome with ocular and central nervous system anomalies. Clinically, nevus psiloliparus is often described as a congenital alopecia and appears as an irregularly shaped, circumscribed area of alopecia on the scalp. Histopathology demonstrates a near-complete absence of mature hair follicles with preservation of arrector pili muscles and mature adipocytes within the dermis. The pathogenesis of nevus psiloliparus may be related to mosaic mutations in fibroblast growth factor receptor 1. Herein we report the histopathological features of a nevus psiloliparus in an 11-year-old girl diagnosed from transverse sections, which show "shadow" follicular units characterized by columns of loosely arranged collagen and a relative paucity of elastic fibers.