Unicentric hyaline-vascular Castleman’s disease in a 29-year-old man. (A) Ultrasonography demonstrated a low echogenic mass 5.4 × 5.2 cm in size (arrow) and there was no significant relationship with the left kidney. (B) Unenhanced CT of abdomen showed a well circumscribed, oval retroperitoneal pararenal mass (arrow) with homogeneous density. (C) Arteriograms showed arterial feeding to the mass from the abdominal aortic. (D) T2WI showed a slightly higher signal and the center of the mass displayed patchy low signal (arrow). (E) Photograph of a cut section of resected specimen demonstrated alternating reddish-brown and gray coloration. The reddish-brown areas represented cell components and the gray areas (arrows) represented fibrous tissue corresponding to the MRI findings. (F) Histological examination of the abdominal tumor (×400). Hyaline degeneration of small vessels with a wide surrounding by lymphoid follicle and lymphocytes arranged in an onion-skin pattern, confirming a diagnosis of Castleman’s disease. Immunophenotyping was positive for CD3, CD10, CD20, CD21, and CD23 antigens.