Hamartoma is a neoplasm-like lesion composed of an abnormal mixture of tissues native to the area. We report on an unusual example of a hamartomatous lesion that showed an abnormal mixture of elements of the folliculosebaceous-apocrine unit and arrector pili muscle. A 13-year-old female presented with two nodules situated 2 cm apart on the lower leg that were present since birth. The patient reported some enlargement and slight pain of the otherwise asymptomatic lesions during 2 years, before they were surgically removed. The patient obviously had no skin problems afterwards; her 12-year follow-up was significant for leucopenia and nephrolithiasis. The biopsies from both lesions looked identical. Each lesion was biphasic, i.e. composed of a predominant mesenchymal component and epithelial elements. The mesenchymal part resembled a leiomyoma, or in minor areas, the constituting cells had a myofibroblastic appearance. Encased within the mesenchymal component were large infundibulocystic structures and plentiful grouped and scattered roundish solid epithelial nodules, duct-like, glandular, and tubular elements. Some of the epithelial structures were reminiscent of those seen in tubular apocrine adenoma; others resembled syringomatous elements. We interpreted this unusual lesion as a hamartoma of the folliculosebaceous-apocrine unit.

Sikl's Department of Pathology Charles University Medical Faculty Hospital Pilsen Czech Republic