A previously healthy 62-year-old woman was taken to surgery for partial thyroidectomy for a suspected colloid nodule. A small level VI lymph node was found incidentally during surgery. The lymph node was 0.5 cm in greatest dimension. The architecture was effaced by a nodular proliferation of neoplastic cells (panel A). The follicles showed a reverse pattern with large centroblasts at the periphery of the neoplastic follicles and the small centrocytes in the center (panel B). Immunohistochemistry was performed on the tissue; the neoplastic cells were immunoreactive with CD20, CD10, bcl-2, bcl-6, and CD21 (panels C-G) and negative for CD3, CD5, and bcl-1. Fluorescent in situ hybridization with break-apart probes showed disrupted bcl-2 (panel H) and bcl-6 genes with an intact C-myc gene.

The patient was diagnosed with follicular lymphoma, grade 3B, follicular pattern. The unique morphologic feature of this case is that of a reverse variant of follicular lymphoma. The reverse (peripheral) grouping of the large cells in the follicles makes grading difficult. Positron emission tomography scan was performed on the patient and showed extensive neck, chest, and abdominal lymphadenopathy with abnormal fludeoxyglucose uptake. At diagnosis, the patient was asymptomatic and this was an incidental finding in a small lymph node.