nevus

Nevus, plural nevi, is a benign pigmented skin lesion resulting from localized proliferation of melanocytes or nevus cells. The term covers a range of growths, from common moles to birthmarks, and nevi can be pigmented, nonpigmented, flat, or raised. Most people have at least a few nevi, and their number often increases during childhood and adolescence. By adulthood, the typical range is about 10 to 40 nevi, though this varies widely.

Nevi are classified by their appearance and by their time of appearance. Congenital nevi are present at birth and vary in size; they carry a higher risk of malignant transformation if large. Acquired nevi develop after birth and are commonly categorized histologically as junctional (melanocytes at the dermoepidermal junction), compound (nests at the junction and within the dermis), or intradermal (nests primarily in the dermis). Blue nevi contain melanocytes in deeper dermal layers and appear blue. Spitz nevi are typically dome-shaped and observed mostly in children; dysplastic (atypical) nevi have irregular borders and color variation and may occur in clusters, sometimes associated with an increased risk of melanoma in syndromes involving many atypical nevi.

Most nevi remain benign, and malignant transformation to melanoma is uncommon but more likely in certain types, such as dysplastic nevi or giant congenital nevi. Diagnosis is usually clinical, aided by dermoscopy; biopsy is indicated for suspicious changes (asymmetry, border irregularity, color variation, rapid growth, or itching) or diagnostic uncertainty.

Management focuses on monitoring, sun protection, and removal when indicated for cosmetic reasons, diagnostic clarity, or suspicion of malignancy. Removal is typically by excisional biopsy; laser ablation is generally not recommended when melanoma cannot be ruled out. Regular follow-up with a clinician is advised for individuals with numerous or atypical nevi.