B

Castleman disease often appears as a solitary, well-circumscribed retroperitoneal mass and may present with low-grade fever but usually without constitutional “B” symptoms or peripheral-blood abnormalities. Histology typically shows hyaline-vascular “onion-skin” mantle zones surrounding germinal centers with prominent, hyalinized penetrating vessels—the classic appearance seen in the provided photomicrograph and not found in NHL, angiolymphoid hyperplasia, or IgG4-related disease. [Sadamoto, 1998, PMID 9745857] [Singletary, 2000, PMID 10675469]