Introduction

RECOGNIZING the many faces of hematologic disease is complicated by the fact that these processes may arise or become most clinically evident in any tissue or organ, and site-specific structure and circumstances have the potential to ‘hide’ the diagnosis. No where is this more true than the spleen. In the era of staging splenectomies, when there was a limited repertoire of special stains and a very simple nosology for splenic neoplasms, pathologists had greater experience with the normal histology of well-preserved spleens and meeting the needs of physicians caring for the patient was a simpler task.

But that era has passed and clinical expectations have increased: disease-specific therapies require disease-specific diagnoses and the list of treatment options for patients with leukemia and lymphoma grows and grows. Simultaneously, there has been an increase not only in the number of recognizable disease categories but also in the number of immunohistochemical markers that may be used to diagnose them, which renders the job of working up the diagnostic splenectomy all the more difficult. An additional challenge is the fact that trainee and staff pathologists alike garner most of their experience with the spleen from the autolyzed remains of the organ at autopsy, and seldom see a surgical specimen unaltered by trauma, infection, steroid or other therapeutic effect. It should therefore be no surprise that we might have difficulty recognizing rare variants of hamartomatous lesions that we might struggle with the boundaries between benign, borderline, and frankly malignant vascular tumors or with the fine distinctions between primary splenic lymphoma and secondary splenic involvement by an as yet undiagnosed lymphoma from another site.

Given that nosology is based in large part on normal counterparts, I have attempted to provide a comprehensive view of normal histology and immuno-architecture in the first section of this update, as a foundation for what comes after. Drs Jayashree Krishnan and Glauco Frizzera, John K. C. Chan, Ahmet Dogan and Peter G. Isaacson, and Jeffery L. Kutok and Christopher D. M. Fletcher, in turn, offer a fresh analysis of both the common and the challenging aspects of splenic pathology. For their superb work, I am most grateful. In putting together this issue of Seminars in Diagnostic Pathology, I am reminded of the observations of an experienced hematopathologist, who spoke recently on the hurdles we face in recognizing patterns of disease. “We see what we know, and what we are able to see is greatly influenced by our concepts, criteria and methods of practice” (B Nathwani, [Morphologic Patterns in Lymph Node Biopsies,] Tutorial for Hematopathology Miami, 2002). I hope that the reader finds the diagnostic approaches and conceptualizations of splenic disease in this update on splenic pathology informative and useful in everyday practice.