Congenital nevus

Congenital nevus is a type of melanocytic nevus (or mole) present at birth or shortly thereafter. These nevi are notable for their potential to develop into melanoma, a form of skin cancer, although the risk varies depending on the size of the nevus. Congenital nevi are categorized based on their size into small (<1.5 cm), medium (1.5-19.9 cm), and large or giant (>20 cm in its largest dimension). The larger the nevus, the greater the risk of melanoma development.

Etiology and Pathogenesis

The exact cause of congenital nevi is not fully understood, but they are believed to result from a combination of genetic and environmental factors that affect melanocyte development in utero. Melanocytes are cells responsible for producing melanin, the pigment that gives skin its color. Anomalies in the proliferation and distribution of these cells lead to the formation of nevi.

Clinical Features

Congenital nevi can vary greatly in size, shape, color, and hairiness. They are typically brown but can range from tan to black, and they may be flat or raised. The surface of a congenital nevus can be smooth, wrinkled, or nodular, and the nevus may or may not contain hair. Large or giant congenital nevi are often accompanied by smaller satellite nevi scattered around the body.

Diagnosis

Diagnosis of congenital nevus is primarily clinical, based on the appearance of the nevus. In cases where the diagnosis is uncertain or if there is suspicion of melanoma, a biopsy may be performed. Dermoscopy, a non-invasive imaging technique, can also be helpful in evaluating nevi.

Management

The management of congenital nevi depends on their size, location, and the risk of melanoma development. Small nevi with no suspicious characteristics may simply be monitored over time. Larger nevi, especially those in cosmetically sensitive areas or those with a higher risk of malignancy, may be considered for removal. Surgical excision is the most common treatment, but for large or giant nevi, this may require multiple surgeries or other techniques such as tissue expansion to achieve satisfactory results.

Prognosis

The prognosis for individuals with congenital nevi is generally good, especially for those with small nevi. However, those with larger nevi have a higher risk of developing melanoma, and regular follow-up with a dermatologist is recommended to monitor for signs of malignancy.

Epidemiology

Congenital melanocytic nevi are relatively common, occurring in approximately 1% of newborns worldwide. The prevalence does not significantly vary between genders or among different ethnic groups.