Follicular Hyperplasia with Castleman-Like Changes Suspicious for Follicular Lymphoma

Lessons From the Friday Unknowns

Histologic sections show multiple lymph nodes in which there are numerous follicles, most of which are small, but with some variation in size.

The follicles are abnormally distributed in the cortex and medulla of the lymph node, and a few follicles are present in perinodal adipose tissue.

Most of the follicles also show Castleman-like changes with regression of germinal centers, decreased germinal center B-cells, increased follicular dendritic cells and some follicles show expanded mantle zones with onion skin-like changes.

Radial arterioles are prominent and show some sclerosis of their walls, but well-developed hyaline vascular lesions are not identified.

The follicles are composed of B-cells, positive for CD20 and PAX-5 and negative for CD3 and CD5. In the germinal centers of follicles, CD10+ cells are greatly decreased but BCL-6+ cells are present. The BCL-6 positive cells are negative for BCL-2. The antibody specific for CD23 highlights many follicular dendritic cells within the follicles. Mantle zone B-cells are negative for CD5. Kappa and lambda highlight scattered polytypic plasma cells that are also positive for MUM1/IRF4. Cyclin D1 and HHV-8 are negative. The antibody specific for Ki-67 highlights germinal center cells and shows that some of the follicles are polarized with dark and light zones. In other follicles replaced mostly by follicular dendritic cells, Ki-67+ cells are decreased and/or pushed to the periphery of the germinal centers.