[1400] Benign Lymphoid Aggregates in the Bone Marrow

K Naemi, RK Brynes, R Dhillon, X Zhao, S Rezk. University of California, Irvine School of Medicine, Orange, CA; Los Angeles County + USC Medical Center, Los Angeles, CA

Background: Benign lymphoid aggregates (BLAs) are seen in approximately 2% of bone marrow specimens. Certain criteria have been proposed to help distinguish between benign and malignant aggregates. Benign aggregates are usually small (<600μm), have distinct borders, and have a random non-paratrabecular location. A detailed description of the distribution patterns of B and T lymphocytes within BLAs has not been investigated.
Design: 136 cases of BLA-containing bone marrow specimens were identified in the pathology files at UCIMC between 1993 and 2009. Of these, 13 cases showed loss of the aggregates on deeper sections. The remaining cases were examined for correlation with various clinical features listed in table 1. A panel of immunostains (CD3, CD20, Bcl-6, CD23, and Ki-67) was performed on all cases. Other additional stains, flow cytometry, and gene rearrangement studies were performed on select cases. The aggregates were categorized based on size, location (paratrabecular or random), and distribution of B and T lymphocytes. Lymphoma cases with malignant aggregates were used for comparison.
Results: Table 1 illustrates the distribution patterns of B and T lymphocytes in relation to our preset variables. In 23 cases originally diagnosed as BLAs, a suspicion of malignancy was raised based on our morphologic criteria. Additional studies and follow-up of these patients confirmed lymphoma in 3 cases with results still pending on some cases.

Table 1
Total casesMostly T cells, T cells in the middle, or mixture of B and T cellsB cells in the middle, or mostly B cells
Infectious diseases40236
Immunologic disorders23147
Associated neoplasms764612
Age <65796314
Age >65523516
*Including cases with germinal center formation

Conclusions: The distribution of B and T lymphocytes within lymphoid aggregates is a useful criterion to separate BLAs from lymphproliferative disease. BLAs are randomly distributed and usually consist of a central core of T cells surrounded by a rim of B cells, or have a mixed distribution of B and T cells. A predominance of B cells within the aggregates, and a central core of B cells surrounded by a rim of T cells (except in germinal centers), paratrabecular location, and large lymphoid aggregates that increase in size in deeper sections are all features that should raise suspicion of a malignant process.
Category: Hematopathology

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 199, Wednesday Afternoon


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