The epithelium is papillomatous and hyperplastic, overlying hamartomatous sebaceous glands. Note areduction in the numbers of mature hair follicles. Sebaceous glands are located high in the dermis, rather than associated with hair follicles.

An abortive hair follicle can be appreciated. Holes(dilated structures) are characteristically seen within the sebaceous gland.

These basaloid proliferations appear similar to primitive hair germs arising from the epidermis.

Nevus sebaceus (a.k.a. organoid nevus, nevus sebacus of Jadassohn) is a hamartomatous lesion composed of abortive and/or abnormally constructed hair follicles, sebaceous glands, epidermis, and sweat glands. It is usually first noticed as a small hairless patch or plaque on the scalp on young children. During puberty, this lesion may become more prominent, verrucous and nodular.

The clinical significance of nevus sebaceus are that benign as well as malignant lesions may arise from it. The most common malignant lesion to develop is basal cell carcinoma whereas the most frequent benign tumor is trichoblastoma. Other associated lesions include syringocystadenoma papilliferum (arising from the apocrine sweat glands), keratoacanthoma, apocrine cystadenoma, leiomyoma, and sebaceous cell carcinoma (Hammaddi).

Histologically, the overlying epidermis is papillomatous and exhibit verruca-like hyperplasia. The dermis contains numerous sebaceous glands, often abnormally placed inserted directly into the epidermis rather than associated with a hair follicle. Increased apocrine lobules and basaloid proliferations are present as well (Busam, Fletcher).

Equal gender predilection. Most common on the the scalp. Other sites include temples, forehead, central face and behind the ears.

Due to the small risk of malignant transformation (as well as cosmetic reasons), excision is usually the recommended treatment.

• Adnexal : Trichoblastoma

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