Castleman’s disease in the retroperitoneal space mimicking a paraspinal schwannoma: a case report

A 33-year-old Japanese man with epigastric discomfort underwent abdominal ultrasonic examination revealing a solid mass next to the right kidney. Computed tomography demonstrated a well-circumscribed mass with central calcification in the right psoas muscle. Because the mass presented a dumbbell-like shape extending to the intervertebral foramen, neurogenic tumor was suspected. Both iodine-123 metaiodobenzylguanidine and gallium-67 scintigraphies were negative in the mass, whereas thallium-201 mildly accumulated in the tumor, suggesting blood flow to the tumor. Positron emission tomography revealed accumulation of fluorine-18-2-fluoro-2-deoxy-d-glucose in the tumor at a standard uptake value of 4.7, whereas no other abnormal uptake suggestive of metastatic lesion was noted. On the basis of imaging studies, we mostly suspected paraspinal schwannoma, although malignancy was not completely excluded. Angiography showed feeding vessels from the right lumbar arteries, which were embolized with porous gelatin particles in order to reduce intraoperative bleeding. Surgical resection was performed using a retroperitoneal approach, which revealed the tumor in the swollen psoas muscle. Intraoperative pathological examination of a frozen section revealed no evidence of malignancy; thus, marginal excision of the tumor was performed. The tumor adhered tightly to surrounding muscle tissues, resulting in 940 g of intraoperative blood loss. The pathological examination demonstrated infiltration of lymphocytes surrounding small germinal centers with extensive capillary proliferation. Immunostaining revealed that proliferated lymphocytes were CD3-negative and CD79a-positive.