A nevus sebaceus is a solitary, well-circumscribed, yellow-orange hairless plaque located on the face or scalp that is a hamartoma of follicular, sebaceous, and apocrine origin.
SYNONYMS Nevus sebaceus of Jadassohn, organoid nevus.
AGE Usually present near birth. May appear in childhood or adulthood. Increase in prominence at onset of puberty.
GENDER M = F.
PREVALENCE Uncommon.
GENETICS Usually sporadic, rare familial forms reported. Mutations in the HRAS and KRAS genes have been identified in sebaceus nevi.
A nevus sebaceus is typically present near birth and has two stages: a prepubertal/infantile stage (Fig. 10-1) and pubertal/adolescent phase (Fig. 10-2).
TYPE Hairless plaque surface may be velvety, verrucous, or papillomatous.
COLOR Yellow, yellow-brown, orange, pink.
SIZE Few millimeters to several centimeters.
SHAPE Round, oval, or linear.
DISTRIBUTION Head and neck.
ARRANGEMENT Solitary lesion; rarely, multiple lesions have been reported.
Typically there are no systemic symptoms. In the scalp, the lesion remains hairless. Rarely, extensive lesions can be associated with ocular, CNS, or skeletal abnormalities. This constellation of extensive sebaceus nevi and associated abnormalities is termed nevus sebaceus syndrome (also known as Schimmelpenning syndrome). The association of nevus sebaceus, CNS malformations, aplasia cutis congenita, ocular limbal dermoid, and pigmented nevus has also been rarely reported and termed SCALP syndrome.
The differential diagnosis includes other appendageal tumors; smaller lesions can resemble warts. Juvenile xanthogranuloma is another benign proliferation with a yellowish-hue also presenting in infancy.
DERMATOPATHOLOGY Infancy: numerous immature sebaceous glands with irregular morphology and cords or buds of undifferentiated hair follicles. Adult: papillomatous hyperplasia of the epidermis with hyperkeratosis and hypergranulosis. There are also typically ectopic apocrine glands located deep in the dermis.
Nevus sebaceus tends to grow slowly and become thicker and more papillomatous with age. Approximately 10% may have benign or, rarely, malignant neoplastic changes that manifest as nodules or ulcers within the lesion: trichoblastoma, trichilemmoma, syringocystadenoma papilliferum (Fig. 10-3) are the most common neoplasms. Other possible growths include sebaceous adenoma, apocrine adenoma, poroma, basal cell carcinoma, and squamous cell carcinoma.
Nevus sebaceus lesions before puberty can be observed regularly for any signs or symptoms of neoplastic change. While there is an increased risk of neoplasms such as syringocystadenoma or trichoblastoma arising within nevus sebaceus, these neoplasms are benign. Only 1% of nevus sebaceus lesions will develop a carcinoma in its lifetime.
More worrisome for the patient is often the progressively verrucous appearance of the lesion or the difficulty of monitoring the lesions in the scalp. Thus deep surgical excision may be warranted. More superficial shave excisions, dermabrasion, or laser ablation are usually not successful, with risk of recurrence for incompletely excised lesions.
A nevus comedonicus is a rare, localized proliferation of the pilosebaceous unit resulting in a well-circumscribed area of comedones.
SYNONYM Comedo nevus.
AGE Present at birth in 50%; others appear before age 10 years.
GENDER M = F.
PREVALENCE Rare.
ETIOLOGY Some familial cases reported. FGFR2 gene mutations identified.
A mesodermal developmental defect of the pilosebaceous unit, the nevus comedonicus is incapable of forming mature terminal hairs. As a result, the sebaceous glands within a nevus comedonicus accumulate cornified debris in numerous dilated follicular ostia.
TYPE Papules, open (blackheads) and closed (whiteheads) comedones (Fig. 10-4). Rarely papules, cysts.
ARRANGEMENT Linear or band-like configuration.
SIZE Individual comedones are on the order of 1 to 2 mm. The extent of the entire nevus comedonicus may range from a few millimeters to several centimeters.
DISTRIBUTION Unilateral solitary lesion on any part of the body. Rarely may have extensive lesions which can present in association with CNS, ocular, or musculoskeletal abnormalities (so-called nevus comedonicus syndrome).
SITES OF PREDILECTION Face, neck > trunk > extremities.
Nevus comedonicus can be confused clinically with comedonal acne, dilated pore, hidradenitis suppurativa, but the congenital onset and localized nature are diagnostic.
DERMATOPATHOLOGY Skin biopsy shows dilated invaginations filled with cornified debris. Associated acute or chronic inflammation may be variably present. Hair shafts are absent.
Nevi comedonicus are usually asymptomatic but can occasionally become inflamed and painful, typically with the hormones of puberty. Pustules, abscesses, and scarring may occur. The lesions persist throughout life but are benign. Rarely, they may be associated with systemic abnormalities (ipsilateral cataract and skeletal defects).
A nevus comedonicus is benign and requires no treatment. Cosmetically, manual comedo extraction can improve the appearance of the lesion. Topical salicylic acid, hydroxy acids, or retinoid preparations help prevent follicular blockage, but the results are not permanent.
Active inflammatory episodes can be managed with topical antibiotics (clindamycin, erythromycin), benzoyl peroxide, or sulfur. In severe cases, oral antibiotics may be helpful.
More permanent results can be achieved with surgical excisions, dermabrasion, or laser ablation, but scarring can result.
Trichoepitheliomas are benign proliferations of follicular germinative (basaloid) cells that appear in childhood as numerous flesh-colored papules on the face and, less often, on the scalp, neck, or trunk.
SYNONYMS Brooke’s disease (multiple familial trichoepitheliomas), epithelioma adenoides cysticum, multiple benign cystic epithelioma.
AGE Early childhood or puberty.
GENDER M = F.
PREVALENCE Uncommon.
GENETICS Autosomal dominant inheritance. Brooke’s disease mapped to multiple gene loci, including 9p21 and CYLD gene at 16q12–13.
Multiple trichoepitheliomas appear during early childhood or at puberty and are asymptomatic but permanent. Multiple trichoepitheliomas are a component of Brooke–Spiegler syndrome and Rombo syndrome when arising alongside other cutaneous neoplasms.
TYPE Firm papules and nodules.
COLOR Flesh-colored, pink.
SIZE Individual lesions typically 2 to 5 mm on face. Lesions may enlarge to 2 to 3 cm on other sites.
SHAPE Round.
NUMBER Few at onset to multiple after puberty (Fig. 10-5).
DISTRIBUTION Face, ears, and trunk.
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