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Sebaceous nevus
Described in 1895 by Jadassohn, nevus sebaceus is a hamartoma of the pilosebaceous unit, consisting of sebaceous glands, sometimes with apocrine glands, and associated with epidermal hyperplasia. Recent studies have revealed post-zygotic somatic mutations in the RAS, KRAS, and HRAS genes.
The prevalence of nevus sebaceus in newborns is 0.3%, with no predilection for either sex. Typically, nevus sebaceus presents at birth as a small patch of hair loss, flat or slightly raised on the skin. It can have a diameter ranging from a few millimeters to a few centimeters, with a rounded or oval shape, and occasionally a linear shape with well-defined edges. The color of the lesion is usually yellowish or yellow-orange, and the surface appears smooth or slightly uneven. The scalp is the most common site of occurrence, but it can also affect the face and neck.
In some cases, the lesion may have a linear shape and be several centimeters wide, often following Blaschko's lines. In such cases, it is important to differentiate between sebaceous nevus and Schimmelpenning syndrome, and to investigate possible extracutaneous manifestations involving the neurological, ocular, and/or skeletal systems. More recently, dental anomalies and involvement of the urinary, endocrine, and cardiovascular systems have also been associated with the syndrome.
Nevus sebaceus tends to enlarge over the years, with growth usually being slight and proportional to the overall body growth. During puberty, the thickness of the lesion may also increase, although the extent of this change varies among individuals. The surface of the lesion may become more uneven and wart-like, and the color may change to yellow-brownish.
Rarely, in the post-pubertal period, a benign tumor of follicular origin may develop on the surface of the nevus, such as trichoblastoma or papillary syringocystadenoma. In less than 1% of cases, a secondary tumor, such as basal cell carcinoma or exceptionally eccrine poroma, may develop. The appearance of secondary tumors generally occurs after the fourth decade of life.
The diagnosis of nevus sebaceus is primarily clinical, and dermatoscopy can be a useful tool. Biopsy is indicated if proliferative lesions appear, as this may be a sign of neoplastic transformation. In most cases, observation over time is recommended, with removal of the nevus in the post-pubertal or adult age for aesthetic purposes or if a tumor develops on the nevus. Laser therapy can be a valid treatment option for smaller lesions or can be combined with surgery.
When there is suspicion of a syndromic form of nevus sebaceus, neurological screening with brain MRI, ophthalmology evaluation, orthopedic examination, and abdominal ultrasound are recommended.
At birth, nevus sebaceus can be differentiated from aplasia cutis by its pinkish-whitish color, flat and smooth surface, and the absence of yellowish globules seen on dermoscopy, which are characteristic of the presence of sebaceous glands in nevus sebaceus.
The prevalence of nevus sebaceus in newborns is 0.3%, with no predilection for either sex. Typically, nevus sebaceus presents at birth as a small patch of hair loss, flat or slightly raised on the skin. It can have a diameter ranging from a few millimeters to a few centimeters, with a rounded or oval shape, and occasionally a linear shape with well-defined edges. The color of the lesion is usually yellowish or yellow-orange, and the surface appears smooth or slightly uneven. The scalp is the most common site of occurrence, but it can also affect the face and neck.
In some cases, the lesion may have a linear shape and be several centimeters wide, often following Blaschko's lines. In such cases, it is important to differentiate between sebaceous nevus and Schimmelpenning syndrome, and to investigate possible extracutaneous manifestations involving the neurological, ocular, and/or skeletal systems. More recently, dental anomalies and involvement of the urinary, endocrine, and cardiovascular systems have also been associated with the syndrome.
Nevus sebaceus tends to enlarge over the years, with growth usually being slight and proportional to the overall body growth. During puberty, the thickness of the lesion may also increase, although the extent of this change varies among individuals. The surface of the lesion may become more uneven and wart-like, and the color may change to yellow-brownish.
Rarely, in the post-pubertal period, a benign tumor of follicular origin may develop on the surface of the nevus, such as trichoblastoma or papillary syringocystadenoma. In less than 1% of cases, a secondary tumor, such as basal cell carcinoma or exceptionally eccrine poroma, may develop. The appearance of secondary tumors generally occurs after the fourth decade of life.
The diagnosis of nevus sebaceus is primarily clinical, and dermatoscopy can be a useful tool. Biopsy is indicated if proliferative lesions appear, as this may be a sign of neoplastic transformation. In most cases, observation over time is recommended, with removal of the nevus in the post-pubertal or adult age for aesthetic purposes or if a tumor develops on the nevus. Laser therapy can be a valid treatment option for smaller lesions or can be combined with surgery.
When there is suspicion of a syndromic form of nevus sebaceus, neurological screening with brain MRI, ophthalmology evaluation, orthopedic examination, and abdominal ultrasound are recommended.
At birth, nevus sebaceus can be differentiated from aplasia cutis by its pinkish-whitish color, flat and smooth surface, and the absence of yellowish globules seen on dermoscopy, which are characteristic of the presence of sebaceous glands in nevus sebaceus.
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