Answer: Castleman’s disease

Histology: The lymph node architecture has been effaced; the sinuses are obliterated by interfollicular vascularization. Germinal centers are small and regressed, composed predominantly of follicular dendritic cells associated with hyaline capillaries. Hyperplastic mantle zones that have a concentric, onion skin-like appearance surround these atretic germinal centers.

Discussion: Follicular lymphoma would be characterized by closely-packed follicles which obliterate the node architecture and are composed of monotonous, small cleaved lymphocytes. Dendritic cells are typically not prominent, the mantle zone is not hyperplastic, and the interfollicular spaces are not vascularized as in the current case. Mantle cell lymphoma may be difficult to distinguish from Castleman’s disease in its nodular phase. In this early phase, the neoplastic mantle cells encircle residual benign follicles. Mantle cell lymphoma often progresses to a diffuse pattern. The prominent interfollicular vascularization, as well as the regressive changes in the germinal centers are not typical of mantle cell lymphoma. Follicular hyperplasia would not efface the node architecture, and would result in enlarged germinal centers which are well polarized.
The current case is an example of a hyaline vascular type of Castleman’s disease. This lesion typically presents as a solitary mass (often mediastinal) in an asymptomatic patient. The lesion does not typically recur after surgery. In contrast, the plasma cell type of Castleman’s disease is often multifocal, is often associated with systemic symptoms like anemia and hypergammaglobulinemia, and is characterized by true follicular hyperplasia with sheets of interfollicular plasma cells. This disorder may persist or, rarely, progress to malignant lymphoma.