Practical Applications in Immunohistochemistry: An Immunophenotypic Approach to the Spleen.

CONTEXT.­: Even though immunohistochemistry is routinely used by pathologists, evaluation of immunohistochemistry in splenic lesions remains difficult for many. Classification of benign and splenic lesions often requires a combination of hematoxylin-eosin evaluation, immunophenotyping, and sometimes molecular testing. Immunohistochemical staining is essential in evaluating many splenic lesions, and requires an understanding of the normal compartments of the spleen. OBJECTIVE.­: To address different immunohistochemical features used for identification and subclassification of different lesions of the spleen, as well as in the normal compartments of the spleen. DATA SOURCES.­: The information outlined in this review article is based on our experiences with a variety of spleen cases, on the current World Health Organization classification of hematopoietic and lymphoid tumors, and on a review of English-language articles published during 2018. CONCLUSIONS.­: Features for phenotyping normal spleen as well as a variety of splenic lesions, including littoral cell angioma and splenic marginal zone lymphoma, are discussed. Suggested immunopanels are provided to assist in the diagnosis of different lesions of the spleen.