A nevus, commonly known as a mole, is a common growth on the skin. These growths form from clusters of melanocytes, which are the cells responsible for producing melanin, the pigment that gives skin its color. Moles can vary in size, shape, and color, typically appearing as brown, tan, or pink spots that can be flat or raised. While most nevi are benign and harmless, sometimes after a mole has been removed, pigmentation can reappear in the same area, a phenomenon known as a recurrent nevus.
Understanding a Recurrent Nevus
A recurrent nevus is a benign proliferation of melanocytes that reappears at the site of a previously removed mole, especially if the removal was incomplete. This repigmentation typically appears within 6 weeks to 6 months after the initial procedure. Clinically, a recurrent nevus can present with varied appearances such as hyperpigmented or hypopigmented areas within the scar, linear streaks, stippled halos, or diffuse pigmentation patterns. While features like irregular borders and uneven pigmentation can sometimes lead to diagnostic confusion with melanoma, recurrent nevi are non-cancerous.
Reasons Nevi Reappear
Nevi reappear after removal because some melanocytes, the pigment-producing cells, are left behind during the initial procedure. This often occurs with superficial removal methods like shave excisions, laser treatments, or cryotherapy, where it is challenging to remove all cells extending deeper into the skin. These residual cells can then multiply and produce pigment, causing the nevus to return in the scar tissue.
The depth of the initial removal directly influences recurrence; procedures that do not penetrate deep enough are more prone to regrowth. For instance, shave biopsies, while cosmetically favorable, often leave deeper melanocytes intact. Hormonal changes, such as those during pregnancy or puberty, can also reactivate mole development in areas where moles were previously removed.
Differentiating Recurrent Nevus from Melanoma
Distinguishing a recurrent nevus from melanoma, a type of skin cancer, is challenging due to overlapping clinical and microscopic features. Recurrent nevi can exhibit irregular shapes and uneven pigmentation, also characteristic of melanoma. Clinically, dermatologists use dermoscopy to examine the lesion. Dermoscopic features suggesting a recurrent nevus include radial lines, pigmentation around hair follicles, symmetry, and centrifugal growth confined within the scar. In contrast, recurrent melanoma may show eccentric hyperpigmentation, a chaotic growth pattern, and pigmentation extending beyond the scar’s edge.
Microscopically, dermatopathologists look for specific architectural and cellular features. Recurrent nevi often display a “trizonal pattern,” characterized by atypical melanocyte proliferation at the dermoepidermal junction, fibrous tissue in the superficial dermis, and sometimes features of a congenital nevus at the base. While recurrent nevi can show some cellular atypia or irregular melanocyte patterns, these are usually confined to the area directly above the scar. Melanoma, however, presents with more significant cellular atypia, high mitotic activity, and a disorganized growth pattern that may involve adnexal structures or extend beyond the scar. Immunohistochemical stains, such as HMB-45 and Ki-67, also assist in differentiation, with recurrent nevi showing a “maturation pattern” and a low proliferative index compared to melanoma.
Clinical Approach to Recurrent Nevi
When a nevus reappears in a scar, a thorough clinical evaluation is performed, often including dermoscopy. If the initial mole was previously biopsied, its pathology report is reviewed for context. The patient’s age and time elapsed since removal are also considered, as recurrent nevi typically appear within months, while recurrent melanomas may take longer.
If there is any doubt about the lesion’s nature, a complete excisional biopsy is often recommended. This allows for a comprehensive pathological review. If the recurrent nevus is confirmed as benign, further treatment is often not needed, though some individuals may opt for re-excision for complete removal or cosmetic reasons. For confirmed benign recurrent nevi with clear clinical and dermoscopic features, periodic monitoring with dermoscopy can be an acceptable management option.