NEVUS WITH THE HISTOLOGIC HALO REACTION
It is better to speak of a nevus having the histologic halo reaction rather than a halo nevus because many of the nevi that have this reaction do not have a halo clinically. There usually is a history of change in such a nevus, however.

The histologic halo reaction is heralded by dense lymphocytic infiltration of the nevus. The nevus cells are often small, and they fade into the lymphocytes in a manner that frequently makes them difficult to distinguish from the lymphocytes. The combination of nevus cells and lymphocytes may expand the superficial dermis to a larger degree than is usually seen in ordinary lichenoid reactions or in dysplastic nevi. Apoptotic keratinocytes can be seen in some cases, and a complete lichenoid reaction with keratinocyte enlargement and Civatte body formation is seen less commonly. Nevus cells are destroyed by the lymphocytes to varying degrees in different nevi. Superficial fibrosis may remain. Cytologic atypia of nevus cells and architectural disorder are occasionally present, and the degree of cytologic atypia  may be disturbing. Peculiar, large nevus cells are seen in some cases.


 
Low power view showing a thick band of superficial lymphocytes.
High power showing Civatte body (smaller arrow) and a cluster of nevus cells (larger arrow)
 Nevus with the histologic halo reaction.

 
 
Low power showing thick lymphocytic infiltrate, epidermal hyperplasia, and keratinocyte enlargement.
High power showing Civatte bodies (magenta globs).
High power showing cluster of nevus cells in junctional area.
Another case of a nevus with the histologic halo reaction. Lichenoid reaction also present.

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