Hematopathology / HISTOPATHOLOGIC FEATURES OF SPLENIC SMALL B-CELL LYMPHOMAS Histopathologic Features of Splenic Small B-Cell Lymphomas A Study of 42 Cases With a Definitive Diagnosis by the World Health Organization Classification

We studied 42 cases of splenic small B-cell lymphoma (SBL) (21 women, 21 men; aged 32-82 years; median, 65 years) with a definitive diagnosis by the World Health Organization classification: chronic lymphocytic leukemia (CLL), 8; mantle cell lymphoma (MCL), 9; follicular lymphoma (FL), 12; marginal zone lymphoma, 13 (splenic [SMZL], 12; extranodal [EMZL], 1). Splenectomy was performed for diagnosis or therapy; splenic weights were 0.2 to 3.8 kg (median, 1.4 kg). In general, splenic SBLs showed white pulp (WP) expansion; morphologic features of the nodules recapitulated the corresponding lymph node histopathologic features. “Marginal zones” were observed commonly in SMZL and FL, may be present in MCL involving the spleen, and may be seen in hilar lymph nodes (HLNs) in SBLs other than SMZL. FL may simulate SMZL and can be distinguished by the presence of neoplastic follicles and HLN morphologic features. Extracellular hyaline deposits (EH) are common in FL and SMZL. MCL typically shows WP expansion by a monotonous small lymphocytic infiltrate, without diffuse red pulp (RP) infiltration or EH; leukemic MCL may show RP infiltration. Splenic morphologic features in CLL vary in WP or RP dominance; marginal zones usually are not observed in CLL. Malignant lymphomas commonly involve the spleen secondarily as part of generalized disease.1,2 Occasionally, lymphomas manifest with prominent splenomegaly, with or without overt evidence of lymphadenopathy, and a splenectomy is performed for diagnostic purposes.3-7 Small B-lymphocytic neoplasms are conceptualized as clonal proliferations of mature small B-lymphocytes, with different subtypes arising from various stages in the life of a mature B cell.8 The differential diagnosis of small B-cell lymphomas (SBLs) involving the spleen can be difficult, especially in cases with prominent splenomegaly only, in which no additional diagnostic interpretation can be made from a lymph node biopsy specimen. The significant differences in therapy and prognosis within various subclasses of SBLs mandate precise diagnostic subclassification.9 While a number of studies have focused on marginal zone lymphomas of the spleen, few studies have compared the different subtypes of splenic SBL after the description of splenic marginal zone lymphomas.10-12 In the most recent study by Piris et al,12 the primary diagnosis in 11 of 33 study cases was made by peripheral blood examination alone, with no supportive flow cytometric immunophenotypic or lymph node histopathologic evidence for the diagnoses of 9 chronic lymphocytic leukemias and 2 mantle cell lymphomas. The objective of our study was to define the morphologic features of SBL involving the spleen by studying the cases of splenic SBL in which a definitive diagnosis and subclassification was established according to the recent World Health Organization (WHO) classification, after integrating all available clinical and pathologic information. Am J Clin Pathol 2003;120:335-347 335 335 DOI: 10.1309/HWG084N3F3LRJ8XB 335 © American Society for Clinical Pathology Kansal et al / HISTOPATHOLOGIC FEATURES OF SPLENIC SMALL B-CELL LYMPHOMAS Materials and Methods