[A Case of Retroperitoneal Primary Castleman's Disease which was Difficult to Differentiate from Liposarcoma].

: A 38-year-old man had a right lower retroperitoneal mass found by abdominal echography in a medical examination, and he consulted the internal medicine of Sumitomo Hospital. On the suspicion of malignant lymphoma, he received a laparotomy with biopsy. Pathological examination revealed that the tumor was either benign lymphadenopathy or low-grade malignant lymphoma, and he was follow-up. Two years later, he was introduced to our department because the follow-up computed tomography revealed signs of a tumor and a mass of adjunctive adipose tissue that increased markedly. Thus, we suspected that the tumor was liposarcoma before the operation, and performed retroperitoneal tumor resection. However, we found that the tumor was pathologically a hyaline vascular type of Castleman's disease and the pathological examination showed no malignant cells in the peritumoral adipose tissue. Since Castleman's disease lacks the characteristic symptoms or image findings, the preoperative diagnosis is generally difficult. Cases with growth of the peritumoral adipose tissue are rare, and the differentiation from the liposarcoma is usually difficult. We discussed how to perform the differential diagnosis of Castleman's disease, and especially about the differential diagnosis of liposarcoma.