Persistent perpendicular pigmentation: a peculiar but specific type of persistent nevus.

Persistent nevi are commonly encountered in clinical and dermatopathology practice. Although they may mimic melanoma on clinical presentation as well as microscopic review, they behave in a benign fashion and are not associated with more aggressive behavior than the original nevus. Persistent nevi may exhibit asymmetry and irregular features that prompt concern for melanoma. However, the relative circumscription and restriction of pigment to the surgical scar provides a valuable clue to diagnosis. Some persistent nevi may have a linear pattern when they are confined to a widening scar. In this situation, the pigment spreads along the lines of skin tension (Langer lines). This unique pattern can be easily identified and should be a reassuring finding. We present a case of persistent nevus with a striking perpendicular pigmentation confined to the scar; the clinical and histologic features of persistent nevi are reviewed.