Desmoplastic Trichilemmoma arising on a Nevus Sebaceous of the Scalp

Abstract

Originally described by Jadassohn in 1895, it was not until 1932 that the term “nevus sebaceous” was introduced by Robinson. It is a prevalent benign congenital hamartoma that classically evolves through discrete phases of growth and that, from the 4th to the 7th decade of life, can give rise in approximately 10 to 30% of cases to several epithelial neoplasms. Very seldom reported in this context, trichilemmomas are benign appendageal tumours that arise from or differentiate toward the outer root sheath epithelium of the normal hair follicle. Usually solitary, they present as verrucous, keratotic or smooth papules on the face, especially in the vicinity of the nose and lips. On clinical grounds, desmoplastic trichilemmomas, a rare benign histological sub-type of trichilemmomas, are easily taken for basal cell carcinomas, intradermal nevi, verrucae, cutaneous horns, sebaceous hyperplasia and squamous cell carcinomas; as far as pathology, differential diagnosis must include the desmoplastic variants of squamous and basal cell carcinomas, as well as trichilemmal carcinoma. A 56 year old Caucasian male presented with several asymptomatic pearly, translucid nodules and papules that had developed over the last 6 months within a congenital alopecic yellowish plaque of his scalp previously diagnosed, on clinical grounds, as a nevus sebaceous. Histopathological examination allowed to disclose a lobular neoplasm with the classic features of desmoplastic trichilemmoma. The case is iconographically depicted and the relevant literature is reviewed.