Nevus sebaceous This congenital lesion is composed of hamartomatous sebaceous glands and abortive hair follicles. It usually presents at birth as a yellow nodule or pebbled, hairless plaque on the scalp, forehead, or neck. Figure 25-1 shows the color and shape of the congenital lesion. With the loss of the effect of maternal hormones during the first few months of life, the lesion may quickly flatten and lose its distinctive color.

During puberty, the nevus sebaceous again becomes raised, yellow, and verrucous. After this change, and usually during adulthood, nevus sebaceous may give rise to a wide variety of benign and malignant neoplasms. These include basal cell hamartomas, keratoacanthomas, syringocystadenoma papilliferum, basal cell epitheliomas, and, rarely, squamous cell carcinomas.

Nevus sebaceous Figures 25-3 and 25-4 illustrate examples of nevus sebaceous occurring on the face, In infancy, facial lesions have a characteristic yellow color and pebbly surface. In both infants, the lesions are linear. Nevus sebaceous, especially when occurring on the face, follows the lines of Blaschko. These lines of normal cell development indicate a form of genetic mosaicism, and are seen in a wide variety of cutaneous disorders.

Widespread nevus sebaceous occasionally indicates a complex syndrome—linear nevus sebaceous syndrome: Patients may develop skeletal, ocular, and neurological abnormalities, Nevus sebaceous syndrome shares features with epidermal nevus syndrome (Figs. 15-53 and 15-54).

Nevus sebaceous Figure 25-5 illustrates an unusual variant-cerebriform nevus sebaceous. The term refers to the “brain-like” convolutions on the surface. The salmon red color is typical for this form of nevus sebaceous.

Figure 25-6 illustrates a syringocystadenoma papilliferum arising within a nevus sebaceous. This is a benign neoplasm.

Nevus sebaceous Figure 25-7 shows another nevus sebaceous on which basal cell carcinoma has developed. In this case, the color appears more brown and blackish in the main lesion, but the yellow color can still be appreciated in the small outlying papules. The nodule near the center represents the malignant change.

Clear cell hidradenoma This benign eccrine sweat gland tumor occurs as a solitary lesion in most cases. Most commonly, the growth appears as a small intraepidermal nodule. Ulceration or discharge of serous material rarely occurs. The lesion is harmless and may easily be excised.

Syringoma These very small papules are adenomas of intraepidermal eccrine ducts. Most commonly, syringomas develop on the eyelids of girls during adolescence. They have no malignant potential, but the lesions are usually multiple and therefore the cause of cosmetic concern.

Figure 25-10 illustrates multiple lesions on the abdomen. Rarely, a child or adolescent will develop successive crops of syringomas on the skin of the anterior neck, antecubital fossa, trunk, axilla, and groin. This condition, termed eruptive syringoma, is sometimes inherited in autosomal dominant fashion. Syringomas may also be seen with increased frequency in patients with Down syndrome.

Dermoid cyst These lesions present in the newborn as soft, round, subcutaneous tumors that may be freely movable or bound down beneath the overlying epidermis. They represent ectodermal hamartomas and occur at the site of closure of embryonic clefts. The vast majority of dermoid cysts are found near the lateral eyebrow or on the forehead. The neck is the next most common location. The lesion pictured in Fig. 25-11 has protruding hair and was present at birth.