Nevus Sebaceous

Abstract

Nevus sebaceous, a hamartoma of the skin and its adnexa, is characterized by epidermal, follicular, sebaceous, and apocrine gland abnormalities. Nevus sebaceous occurs in approximately 0.3% of all newborns. Both sexes are equally affected. The early infantile stage is characterized by papillomatous epithelial hyperplasia. The hair follicles are underdeveloped and the sebaceous glands are not prominent. During puberty, sebaceous glands become numerous and hyperplastic, apocrine glands become hyperplastic and cystic, and the epidermis becomes verrucous. The hair follicles remain small and primordial and may disappear altogether. During adulthood, epidermal hyperplasia, large sebaceous glands, and ectopic apocrine glands are characteristic histological findings. At birth, nevus sebaceous typically presents as a solitary, wellcircumscribed, smooth to velvety, yellow to orange, round or oval, minimally raised plaque. The scalp and face are sites of predilection. Lesions on the scalp are typically hairless. At or just before puberty, the lesion grows more rapidly, becomes more thickened and protuberant, and at times acquires a verrucous or even a nodular appearance. Nevus sebaceous may be complicated by the development of benign and malignant nevoid tumors in the original nevus. Neoplasms occur mostly in the fourth decade of life in approximately 10 to 30% of lesions. The majority of these tumors are benign; less than 1% of nevus sebaceous is complicated by malignant tumors. Because of the potential of malignant transformation, prophylactic full–thickness, complete excision of the lesion with 2 to 3 mm margins or ongoing observation is recommended.

Keywords: Nevus sebaceous; Sebaceous glands; Plaque; Neoplasms; Prophylactic excision

Introduction

Nevus sebaceous, also known as nevus sebaceous of Jadassohn, 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 Josef 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 also been coined [3,4].

Epidemiology

Nevus sebaceous occurs in approximately 0.3% of all newborn infants [1]. Both sexes are equally affected [5]. There is no racial and⁄ or ethnic predominance [2]. Recent studies suggest a possible link with mothers positive for human papillomavirus [4]. The occurrence of the nevus is usually sporadic, although familial cases have rarely been reported. An autosomal dominant mode of inheritance has also been described [6].

Pathogenesis

Recently, it has been shown nevus sebaceous is caused by post zygotic mosaic mutations in the HRAS and KHAS genes [7]. Presumably, nevus sebaceous develops from pluripotent primary epithelial germ cells which have the potential to differentiate into various neoplasms [5]. Deletions in the PTCH tumor suppressor gene on chromosome 9p22.3 may account for the neoplastic potential of the hamartoma [5,8].

There is an increased expression of androgen receptors in nevus sebaceous [9]. The growth of the lesion in adolescence is due to increased production of androgen at the time of puberty and its influence on the pilosebaceous and apocrine elements.

Histopathology

The early infantile stage is characterized by papillomatous epithelial hyperplasia [10]. The epidermis is only slightly acanthotic [11]. The hair follicles are underdeveloped and the sebaceous glands are not prominent [1,10]. 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 [1,10,11]. The hair follicles remain small and primordial and may disappear altogether [1,11]. During adulthood, epidermal hyperplasia, large sebaceous glands, and ectopic apocrine glands are characteristic histological findings [11]. Normal hair follicles are characteristically absent [11]. This stage is also distinguished by the potential development of a variety of adnexal tumors [11].

Clinical Manifestations

Approximately two thirds of cases are present at birth and the rest develop in early childhood. At birth, nevus sebaceous typically presents as a solitary, well–circumscribed, smooth to velvety, yellow to orange, round, oval, or linear, flat or minimally raised, plaque (Figure 1) [2,3]. Lesions on the scalp are typically hairless [12]. Rarely, the lesion may be pedunculated [9]. The lesions are often distributed along Blaschko’s lines and are arrayed in a linear configuration. This may be difficult to appreciate if the lesion is small. The scalp and face are sites of predilection, although the trunk and extremities may also be affected [1–3]. Rare intraoral extension may present as a linear whitish plaque. Characteristically, the lesion grows proportionally with the size of the patient until puberty [13]. At or just before puberty, the lesion grows more rapidly, becomes more thickened and protuberant, and at times acquires a verrucous or even a nodular appearance [1,2,12]. Nevus sebaceous is usually solitary, although multiple and widespread lesions have been reported [14].

Figure 1: Nevus sebaceous presenting as a yellow-orange, linear, hairless plaque on the scalp.