Targetoid hemosiderotic nevus. A trauma-induced simulator of malignant melanoma.

Background: Simulators of malignant melanoma comprise a heterogenous group of melanocytic and nonmelanocytic lesions of the skin. Among frequent clinical mimickers of melanoma are injured melanocytic nevi. Any change in the clinical appearance of a pre-existing nevus should alert the clinician to exclude the possibility of malignant transformation in order to early identify a lesion at a stage when complete cure can still be achieved.

Objective: The purpose of this study was to present the clinical, dermoscopic and histopathologic findings of a series of acquired melanocytic nevi which abruptly developed a pigmented peripheral halo, presumably following minor trauma.

Methods: A series of 6 cases of acquired melanocytic nevi which suddenly developed a targetoid halo were included in the study. All lesions were evaluated by dermoscopy. Three cases were surgically removed at different stages of evolution and submitted to histopathologic examination. In all cases, follow-up was obtained.

Results: All the lesions arose on trauma-prone skin sites of young women. The sudden development of an asymptomatic, targetoid halo on a long-lasting, acquired exophytic nevus was the main presentation. Whereas the central nevus persisted, the ecchymotic halo ultimately disappeared. Histopathologic examination disclosed changes of the traumatized nevus in the central part, whereas the ring showed hemorrhage and hemosiderin deposits. Increased numbers of small vessels with hobnail characteristics were associated features.

Conclusions: Targetoid hemosiderotic nevus is a distinctive clinicopathologic variant of traumatized acquired melanocytic nevus which should be included in the list of clinical simulators of melanoma.