Splenic histology and histopathology: an update

The spleen can be a troublesome specimen for the surgical pathologist, not only because experience with the range of "normal" splenic histology is limited by its rarity but also because there is an often a frustrating discordance between the patient's clinical condition and the perceived findings. Patients with a dramatic clinical presentation that points to splenic pathology ("hypersplenism" or marked splenomegaly) not infrequently have no discernable or have barely perceptible histologic abnormalities of the spleen. Similarly, patients whose spleens contain histologic findings that seem to deviate significantly from the "norm" (histiocytic proliferations, vasoformative lesions, stromal hyperplasia) may have no clinically detectable hematologic complaints. For most pathologists, the frame of reference for normal splenic histomorphology derives largely from experience with autopsy spleens and spleens removed for trauma or immune thrombocytopenia. These are all settings in which pre-existing disease, the immune status of the patient, and therapy influence the findings and--in cases in which fixation has been delayed--even the ability to make the findings. This review presents practical aspects of splenic development and immunoarchitecture and relates this to the pathologist's approach in evaluating the abnormal spleen and assists in resolving such discordances. Benign conditions that contrast with the subjects of subsequent articles in this issue are emphasized.