Castleman's Disease of the Renal Sinus Presenting as a Urothelial Malignancy: A Brief Case Report

Castleman's disease is a rare benign lymphoproliferative disorder that frequently affects lymph nodes of the mediastinal thorax and the neck. It very rarely affects the renal sinus. We report a case of Castleman's disease arising in the renal sinus in a 64-year-old man. The patient visited the hospital with the chief complaint of hematuria. Abdominal computed tomography revealed a homogeneous mass in the sinus of the left kidney, radiologically interpreted as a malignant urothelial tumor. Subsequently, nephroureterectomy was performed, after which microscopic examination of the specimen revealed a diffuse lymphoproliferative lesion with reactive lymphoid follicles of various sizes and prominent plasma cell infiltration of interfollicular spaces, highlighted by immunohistochemical staining for CD138. The lesion was diagnosed as Castleman's disease of the plasma cell type. Although preoperative diagnosis of Castleman's disease is difficult and the incidence is exceedingly rare, it should be considered in the differential diagnosis of renal sinus tumors.