Nevus sebaceous (NS)
Nevus sebaceous (NS) is a congenital hamartoma of the sebaceous glands that was first described by Josef Jadassohn , MD, in 1895. The lesion is caused by a post-zygotic somatic mutation in the KRAS or HRAS genes, which can lead to variable clinical mosaicism. In addition, hamartomatous presentations within different cell lines may occur if the pluripotent stem cells are affected. The lesion is present in about 0.3% of newborns and is equally represented among gender, race, and geography.
NS has three stages of presentation. At birth or early childhood, NS most commonly presents as a solitary, well-circumscribed, smooth, yellow to tan-brown plaque with associated hair loss in the vertex of the scalp, although it may less commonly present on the face, neck, or trunk. The lesion may be raised at birth. During puberty, hormonal variations alter the form of the lesion and the NS can become more verrucous and nodular. The clinical differential diagnosis for NS includes seborrheic keratosis, congenital nevus, and epidermal nevus.
About 24% of patients may develop appendageal tumors arising from the primary lesion. The majority of these tumors are benign, with trichoblastoma and syringocystadenoma papilliferum as the most common secondary growths. The most common malignant tumor that arises is basal cell carcinoma. Deletion of the patched gene has been implicated in the development of basal cell carcinoma within NS lesions. Many other tumors arising from NS lesions have been reported in the literature, including keratoacanthoma, apocrine cystadenoma, leiomyoma, and sebaceous cell carcinoma. More rarely, development of an eccrine or apocrine carcinoma within the NS can lead to widespread metastasis and death.
Because there is a chance of secondary tumor development, the decision to surgically excise the lesion or closely follow for transformation is controversial. Advocates of surgical excision reason that adolescence is the optimal time for removal because it is before pubertal enlargement and the patient would be able to tolerate anesthesia. If the patient chooses to clinically monitor the lesion, he or she should be informed that a full-thickness excision with wide margins will have to be performed if malignant transformation occurs.
A biopsy was performed of the erythematous papule that revealed an atypical sebaceous neoplasm with features of a sebaceoma. The patient had subsequent excision of the entire lesion that was read by a different dermatopathologist and revealed nevus sebaceous with syringocystadenoma papilliferum, no residual atypical sebaceous neoplasm, and clear margins.
This case and photo were submitted by Victoria Billero, University of Miami, and Dr. Bilu Martin.
Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at edermatologynews.com. To submit a case for possible publication, send an email to [email protected].