Young Boy With Bald Patch
A 4-year-old boy with asymptomatic lesion on his scalp since birth. Pregnancy uncomplicated. No history of trauma or dermatitis in the involved area. Child otherwise healthy and not taking any medication.
Vital signs normal. Circular, light orange to tan-colored, velvety, hairless patch on the vertex of the scalp. Remaining examination findings unremarkable. In particular, no other developmental defects noted.
WHAT’S YOUR DIAGNOSIS?
Answer: Nevus Sebaceous
Nevus sebaceous, a hamartoma of the skin and its adnexa, is characterized by epidermal, follicular, sebaceous, and apocrine gland abnormalities.1 The condition was first described by Jadassohn, a German dermatologist, and now bears his name.2 Because the lesion involves more than just a sebaceous component, the more encompassing term “organoid nevus” has been coined.3
Nevus sebaceous occurs in about 0.3% of all newborns.1 Both sexes are equally affected.4 There is no racial or ethnic predominance.2
The exact pathogenesis is unknown. Presumably, nevus sebaceous develops from pluripotent primary epithelial germ cells, which have the potential to differentiate into various neoplasms.4 Deletions in the PTCH tumor suppressor gene on chromosome 9p22.3 may account for the neoplastic potential of this hamartoma.4,5
The early infantile stage is characterized by papillomatous epithelial hyperplasia.6 The epidermis is only slightly acanthotic.7 Hair follicles are underdeveloped and sebaceous glands are not prominent.1,6 Apocrine glands are rarely seen.1
During puberty, sebaceous glands become numerous and hyperplastic, apocrine glands become hyperplastic and cystic, and the epidermis becomes verrucous—probably because of the influence of andogens.1,6,7 Hair follicles remain small and primordial and may disappear altogether.1,7
Histological findings during adulthood include epidermal hyperplasia, large sebaceous glands,
and ectopic apocrine glands.7 Normal hair follicles are characteristically absent.7 This stage is also
distinguished by the potential development of a variety of adnexal tumors.7
About two-thirds of cases are present at birth, the rest develop in early childhood. At birth, nevus
sebaceous typically presents as a solitary, well-circumscribed, smooth to velvety, yellow to orange, round or oval, minimally raised plaque (Figures 1 and 2).2,3 The scalp and face are sites of predilection.2,3 Rarely, the trunk and extremities may also be affected.1
Lesions on the scalp are usually hairless.1,2 At or just before puberty, the lesion grows and appears verrucous or even nodular.1,2 A new phenotype characterized by large, pedunculated or verrucous, pink nodules or tumors in the neonatal period has recently been described.8,9
Occurrence of the nevus is usually sporadic and an isolated finding. Nevus sebaceous accompanied by eye and brain abnormalities is referred to as Schimmelpenning-Feuerstein-Mims syndrome (linear nevus sebaceous syndrome). Patients with this syndrome may also have epilepsy, mental retardation, skeletal defects, cardiovascular abnormalities, and urologic abnormalities.
The diagnosis of nevus sebaceous is usually clinical based on the characteristic features.
The lesion can be aesthetically unappealing, especially when it occurs on the face. Children born with large nevus sebaceous are at increased risk for other developmental defects.9
Benign and malignant nevoid tumors may develop in nevus sebaceous (Table).1 The incidence of these tumors increases with age, particularly after puberty.7 Neoplasms occur mostly in the fourth decade of life in about 10% to 30% of lesions.3,4 Most of these tumors are benign; fewer than 1% of nevus sebaceous tumors are malignant.4 Malignancy is suggested by the acute appearance of a large, discrete, ulcerating nodule within the lesion.3
Excision of the lesion may be considered at any age for cosmetic reasons. Because of the potential for malignancy, some authors recommend prophylactic full-thickness, complete excision of lesions with 2 to 3-mm margins in young children.1,2,10 However, with the incidence of malignant transformation being low in childhood, prophylactic excision of the lesion before puberty is controversial.4,9,11