Nevus sebaceous is a birthmark present from birth, often appearing on the scalp or face. It represents a localized overgrowth of skin components, primarily sebaceous glands, hair follicles, and epidermal cells. While generally benign, it can undergo changes over a person’s lifetime.
Characteristics of Nevus Sebaceous
Nevus sebaceous appears as a smooth, yellowish-orange to tan patch on the skin during infancy. Its texture can be waxy or velvety. The lesion is often hairless, especially on the scalp, contrasting with surrounding hair. These birthmarks range from a few millimeters to several centimeters in size, and their shape can be round, oval, or linear.
The most common locations are the scalp and face, particularly the forehead or cheek. They can also appear on the neck or other body parts. This birthmark is an organoid nevus, meaning it involves the abnormal development of multiple skin structures. The primary component is an excess of sebaceous glands, which produce skin oil.
How Nevus Sebaceous Develops
Nevus sebaceous originates from a localized genetic change during fetal development. This alteration is not inherited but arises spontaneously in affected skin cells. This leads to the characteristic overgrowth of sebaceous glands and other skin elements. The lesion is present at birth, though it may be subtle in newborns.
During childhood, the nevus sebaceous generally remains stable or grows proportionally. Significant changes often occur around puberty due to hormonal influences. The lesion may become thicker, more elevated, and develop a bumpy or warty texture as sebaceous glands enlarge. This transformation is a typical part of its natural progression and does not indicate a concerning change.
Diagnosis and Management
Diagnosing nevus sebaceous relies on its characteristic appearance during a physical examination. Its distinct color, texture, location, and hairless nature often provide sufficient clues for diagnosis. If the appearance is atypical or concerning changes occur, a skin biopsy may be performed. This involves taking a tissue sample for microscopic examination to confirm diagnosis and rule out other conditions.
Management often involves observation, especially for smaller lesions without symptoms. Regular monitoring helps detect unusual changes in size, color, or texture. Surgical removal may be considered for cosmetic concerns, recurrent irritation or bleeding, or secondary growths within the nevus. Excision is often performed in childhood or adolescence, especially before puberty if cosmetic concerns are significant.
Potential Secondary Growths and Syndromes
While nevus sebaceous is a benign condition, it carries a low potential for secondary growths to develop within the lesion. These are most commonly benign tumors, such as syringocystadenoma papilliferum or trichoblastoma, appearing as new bumps or nodules within the birthmark. Malignant transformations, such as basal cell carcinoma, are exceedingly rare, occurring in less than 1% of cases, typically in adulthood.
In extremely rare instances, an extensive nevus sebaceous, particularly a large, linear lesion, can be associated with Nevus Sebaceous Syndrome (Schimmelpenning-Feuerstein-Mims syndrome). This syndrome involves abnormalities affecting other organ systems, including the brain, eyes, or bones. This syndrome is exceptionally uncommon, and most individuals with nevus sebaceous do not develop associated systemic issues.