Lymphoid cell aggregates: a useful clue in the fine-needle aspiration diagnosis of follicular lymphomas.

Among the various types of lymphoma, follicular lymphoma (FL) is known to have significant limitations in cytologic diagnosis by the fine-needle aspiration (FNA) method. The diagnostic accuracy (DA) for non-Hodgkin's lymphoma (NHL) by FNA was evaluated by review of 82 cases of histologically proved NHL after prior FNA. The DA for all NHLs was 66% (54/82), and that for low-grade lymphomas, including small lymphocytic lymphoma, follicular small-cleaved cell lymphoma, and follicular mixed cell lymphoma, was 71% (12/17). The DA for FL was 69% (11/16). Review of individual surgical and cytologic materials from FLs revealed a tendency to show fibrosis in the cytologically false-negative group and diffuse areas of lymphoma in the true-positive group. The presence of "aggregation" of uniform lymphoid cells, probably due to cell adhesions with the support of dendritic reticulum cells, was seen in 55% of true-positive FL (6/11). In contrast, only 28% of true-positive diffuse large cell lymphomas (5/18) showed a mild degree of aggregation, and none of 7 cases of true-positive diffuse small-cleaved cell lymphoma showed this feature. The aggregation of cells was not pathognomonic of FL, but its presence with a homogeneous cellular constituent and the paucity of tingible-body macrophages helped us to predict FL. Also, it was a feature distinguishing FL from diffuse small-cleaved cell lymphoma (P = 0.025).