Nevus Sebaceous · What Are They, Causes, Signs and Symptoms, and More

Nevus sebaceous, also called nevus sebaceous of Jadassohn or organoid nevus, is a benign tumor that arises from the skin and its appendages, including hair follicles, sebaceous glands, and surrounding connective tissue. It most commonly presents at birth as a waxy, yellow-orange or tan, hairless plaque on the scalp, face, or neck. While completely benign, some nevus sebaceous develop secondary tumors that may warrant surgical excision.

Nevus sebaceous are thought to be caused by mutations in the HRAS or KRAS genes and growth factors like the FGFR2 gene. The RAS pathway takes part in many cellular processes including cell division, cell growth, and programmed cell death. With nevus sebaceous, RAS gene mutations only affect a specific line of cells that gives rise to the tissues forming the skin. The reason for this is that these mutations are not inherited, but rather acquired during embryological development. The earlier the mutation arises in embryological development, the more tissues will be affected, since more tissues will originate from the mutant cells. This is an example of somatic mosaicism, where individuals have some cells in their body with the mutation and others with the normal gene, like a mosaic.

Nevus sebaceous are usually present at birth or early childhood and appear as a patch of overgrown skin on the scalp, face, or neck. In light skin tones, they have a yellowish-orange appearance, while in dark skin tones, they can appear light or dark brown. Most lesions are hairless due to the absence of mature hair follicles and have a smooth, velvety surface. During adolescence, sebaceous nevi become more prominent and acquire a verrucous or wart-like appearance due to increased activity of the sebaceous, or oil-producing, glands.

Around 10 to 20% of sebaceous nevi develop secondary tumors which can be benign or malignant. Most of these tumors consist of trichoblastomas, which are benign tumors that arise from immature hair follicles. Other common tumors include syringocystadenoma papilliferum and sebaceous adenoma, both of which are benign tumors that arise from sweat glands. The most common malignant tumor is basal cell carcinoma (BCC), but other types of skin cancer, such as squamous cell carcinoma (SCC) and sebaceous carcinoma, may also occur.

Although rarely, nevus sebaceous may be a characteristic of congenital syndromes, such as epidermal nevus syndrome and Schimmelpenning-Feuerstein-Mims syndrome. These disorders share the presence of large sebaceous nevi along with disorders affecting the eyes, brain, and skeletal system.

Nevus sebaceous are often diagnosed clinically based on their appearance. Trained clinicians may also use a dermatoscope, which is a tool that can magnify skin lesions and emit a special light to help detect features that are not visible to the naked eye. Upon dermatoscopy, nevus sebaceous typically show a white or yellow globular appearance sometimes with small brown aggregates. These characteristics can help distinguish nevus sebaceous from other skin conditions, including other types of epidermal nevi, alopecia plaques, and certain types of skin cancer. If the diagnosis is unclear, or if there is an increased risk of malignancy, a biopsy may be warranted to examine the lesion under the microscope.

Most nevus sebaceous do not require treatment other than monitoring for any changes within the lesion. Changes during childhood are rare and may warrant a biopsy to rule out malignancy. Surgical excision can be done in cases of secondary tumors or for cosmetic concerns although some surgeons may opt to surgically remove the lesion before any dysplastic changes have developed to avoid the risk of malignant transformation in the future.

Other treatments, such as lasers, peels, or dermabrasion procedures, are not recommended since they do not remove the entire lesion leaving the risk of malignant transformation. Finally, recent research suggests topical treatment with sirolimus, an mTOR inhibitor, may help flatten the lesions to improve their appearance. This might be an appropriate treatment option for individuals who do not desire surgical excision.

Nevus sebaceous of Jadassohn (NSJ) is a benign skin tumor that is usually present at birth and often resembles a birthmark. It presents as a waxy, skin-colored plaque on the scalp, face, or neck, which can change in appearance and color during adolescence due to hormonal changes. In a small number of cases, nevus sebaceous may develop secondary tumors, both benign and malignant, which is why monitoring is recommended. Diagnosis of sebaceous nevi is clinical and treatment includes surgical excision in cases of unusual changes or cosmetic concerns. Other treatments, such as topical sirolimus, may be an option to improve the appearance of the lesion in individuals who do not desire surgical excision.