Halo Nevus ? the Vascular Connection

Abstract Background: Halo Nevi (HN), are defined as benign melanocytic nevi that are surrounded by a rim of depigmentation, resembling a halo. The halo phenomenon indicates the involution and subsequent regression of the melanocytic nevus. Material and Methods: A random series of 137 nevi, including 75 HN were examined. Serial paraffin and frozen sections were subjected to: routine histochemistry; (HE, Reticulin, Auro, PAS), enzyme histochemistry: dopa oxidase, counterstained with Nuclear Fast Red (NFR) to highlight the endothelium and dopamine oxidase; immunohistochemistry to assess presence of lymphocytic infiltrates; electron microscopy: after enbloc dopa stain. Results and Discussion: Junctional nevi show proliferation of highly dendritic melanocytes within the epidermis. Intradermal nevi are composed of dermal nevus cells separated from the epidermis by a clear Grenz zone. Compound nevi show a combination of junctional activity and sheets of dermal nevus cells. Some nevi show a depigmented halo and can regress completely to be replaced by a depigmented patch, the halo nevus. The nevus cells and marginal melanocytes are replaced by endothelial cells, lining vascular spaces, with involution of the nevus. Intriguingly there is a complete absence of inflammatory and immune related lympho-histiocytic cells in the cases studied. These observations, suggest that nevus cells are replaced by vascular endothelial cell types which results in dissolution of the lesion.