Granulomatous inflammation in nevi undergoing regression (halo phenomenon): a report of 6 cases

Halo phenomenon is a process whereby a melanocytic nevus undergoes regression with or without a clinically evident halo. It is now well established that cell-mediated immunity and to a lesser extent humoral immunity are integral to the development of halo nevi. We report 6 cases of nevi exhibiting halo phenomenon with granulomatous inflammation received in our dermatopathology practice over a 7-month period. Of these 6 cases, clinical evidence of a halo was documented in 2 of the nevi. In none of the cases was there a mention of granulomatous inflammation by the referring pathologist. Despite an extensive review of the literature, we did not find a report of overtly granulomatous inflammation occurring in regressing nevi, although we encounter the phenomenon not uncommonly in our practice and believe that practicing dermatopathologists should be aware of it.