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Nevus sebaceus_0212 Derm Clin 2
A boy aged 3 years was brought to the pediatric dermatology clinic with a lesion on his scalp that was first noted shortly after birth. The lesion was originally thought to be attributable to a scalp electrode that had been placed during delivery.
The lesion was asymptomatic and seemed to be growing proportionately with the boy. The child’s parents were concerned that no hair grew within the area and asked about treatment options to improve the cosmetic appearance of the lesion. On physical examination, a large salmon-colored plaque was appreciated on the vertex of the scalp. What’s your diagnosis?
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First described in 1895, nevus sebaceus is often thought of as a sebaceous malformation. However, the condition is better described as a circumscribed hamartomatous lesion that has follicular, sebaceous and apocrine malformation to varying degrees.1 A hamartoma is defined as a benign, focal malformation that resembles a neoplasm in the tissue of its origin.
Nevus sebaceus is also referred to as “organoid nevus.” Today, the lesion is known to be a congenital malformation and presents as a solitary hairless plaque found mainly on the face and scalp.
Nearly all lesions of nevus sebaceus are present at birth. As the infant grows into a child, the lesions will also grow and become more apparent. The probability of developing a nevus sebaceus seems to be random among the patient population. There are a few forms that do run in families, but these are uncommon. Approximately 0.3% of newborns will be affected by a nevus sebaceus.2,3 There is no evidence to suggest that the disorder favors a particular sex or race. There is no involvement of any other organ system.
The disorder stems from a principal malformation of individual folliculosebaceous entities. Research shows postzygotic somatic mutations result in the various clinical expressions of mosaicism (i.e., cells with a different genetic makeup). The pluripotent cells give rise to harmartomas with multiple cell lines.4
Extensive nevus sebaceus may be associated with multiple systemic abnormalities, in which case it is referred to as “nevus sebaceus syndrome,” defined as the combination of extensive sebaceous nevi with systemic abnormalities that affect the central nervous system, bone and eye. This may manifest as epilepsy, mental retardation or other neurologic defects. Also seen are such skeletal deformities as spina bifida or bone hypertrophy and such ocular abnormalities as ptosis, nystagmus and oculomotor dysfunction.
At birth, a nevus sebaceus may be very subtle. Lesions begin as thin, salmon-colored plaques on the scalp or face. However, there have been cases in which the neck or trunk was affected. At puberty, hormonal changes cause the sebaceous glands to become more active, and the surface of the nevus sebaceus often becomes greasier and thicker and develops a verrucous surface.3,4 The lesions are distributed in a linear configuration that follows the lines of Blaschko.3 This may be difficult to appreciate if lesions are small.
Histologically, the sebaceous glands are well developed during infancy due to maternal hormonal influences. In childhood, the sebaceous glands are reduced in number and size, and the diagnosis may be missed when examining the skin microscopically. The hair structures must be carefully analyzed, because there will often be undifferentiated cells mimicking the embryonic stage of hair follicles,5,6 which may provide a clue to the diagnosis.
At puberty, hormonal influences allow the lesion to assume its diagnostic histologic appearance. An abundance of mature sebaceous glands will be found underneath a papillomatous hyperplasia of the epidermis. These sebaceous glands are often unassociated with mature hair shafts.5 Ectopic apocrine glands will develop in about two thirds of patients at puberty.6 The apocrine glands are located deep in the dermis below the abundant sebaceous glands. Often, there are malformed hair germs that appear as buds of undifferentiated cells that resemble foci of basal cell carcinoma (BCC).
During adulthood, various tumors may develop secondarily within the nevus sebaceus. The most commonly associated tumor was once thought to be BCC. However, reevaluation has led researchers to believe that these were actually misdiagnosed cases of trichoblastoma. Currently, trichoblastoma is thought to be the most commonly associated tumor, with BCC occurring only rarely. Syringocystadenoma papilliferum has been found in 8%-19% of nevus sebaceus lesions.6
Other tumors that may develop — but are much less commonly seen — include nodular hidradenoma, syringoma, sebaceous epithelioma, chondroid syringoma, trichilemmoma, trichoadenoma, sebaceous carcinoma, squamous cell carcinoma, eccrine poroma and proliferating trichilemmal cyst.
Similar lesions that may be mistaken for nevus sebaceus include epidermal nevi, congenital nevi, sebaceous adenoma, sebaceous carcinoma, aplasia cutis congenita, seborrheic keratoses and verruca vulgaris. When considering the diagnosis of epidermal nevus, keep in mind that although both may appear similar clinically, epidermal nevi are found mainly on the extremities and trunk of the body. Histologically, there is no proliferation of sebaceous or apocrine glands.6
It was previously thought that approximately 10% of nevus sebaceus lesions would undergo malignant transformation into BCC (or other types of carcinoma).7 Complete surgical excision was recommended because of this risk. However, new research shows that the only about 1% of the lesions may develop into a malignant carcinoma.3
Most patients desire removal for cosmetic reasons. The excision needs to be conservative but still reach the adipose tissue or galea. Complete excision of the lesion will prevent the development of secondary neoplasms.8 For facial lesions, consider excision during childhood while the lesions are small and have not developed secondary verrucous changes. Early excision will help minimize scarring. Treatment with shaving and laser ablation has been attempted but with minimal success.3
The prognosis for those who are diagnosed with nevus sebaceus is excellent. Most lesions may be monitored over time for malignant progression. If it is cosmetically undesirable or in an area where monitoring may be difficult, complete surgical excision is curative.
In this case, extensive education and anticipatory guidance regarding the diagnosis of nevus sebaceus was given to the child’s parents. Given the lesion’s large size and concern for cosmesis, a referral was made to plastic surgery to discuss options for removal.
Kerri Robbins, MD, is a resident in the Department of Dermatology at Baylor College of Medicine in Houston. The author has no relationships to disclose relating to the content of this article.
References
1. Prioleau PG, Santa Cruz DJ. “Sebaceous gland neoplasia.” J Cutan Pathol. 1984;11:396-414.
2. Habif TP. Skin Disease: Diagnosis and Treatment. 2nd ed. St. Louis, Mo: Mosby/Elsevier; 2005:408-411.
3. Bolognia JL, Jorizzo JL, Rapini RP, eds. Dermatology, 2nd ed., St. Louis, Mo.: Elsevier-Mosby; 2008:1695-1696.
4. Paller AS, Mancini AJ. Hurwitz Clinical Pediatric Dermatology. 3rd ed. Philadelphia, Pa.: Elsevier Saunders; 2006:221-222.
5. Rapini RP. Practical Dermatopathology. Philadelphia, Pa.: Elsevier Mosby; 2005:281-282.
6. Elder DE, Elenitsas R, Johnson BL et al, eds. Lever’s Histopathology of the Skin. 10th ed., Philadelphia, Pa.: Lippincott Williams & Wilkins; 2009:870-874.
7. Cribier B, Scrivener Y, Grosshans E. “Tumors arising in nevus sebaceus: A study of 596 cases.” J Am Acad Dermatol. 2000;42:263-268.
8. Chun K, Vázquez M, Sánchez JL. “Nevus sebaceus: clinical outcome and considerations for prophylactic excision.” Int J Dermatol. 1995;34:538-541.
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