a 64-year - old man visited our hospital with the chief complaint of microscopic hematuria for the past 2 months . abdominal computed tomography ( ct ) revealed a homogeneous solid tumor with slightly low attenuation in the left renal sinus ( fig . altogether , these abdominal ct findings were suggestive of invasive urothelial carcinoma arising in the left pelvis with involvement of renal sinus soft tissue . nephroureterectomy was performed , and the cut surface of the renal sinus revealed a grayish - white solid tumor of rubbery consistency . the tumor was primarily located in the renal pelvis , but extensions to the renal calyces and proximal ureter were suspicious . the pelvic tumor mass measured 42.5 cm and exhibited peripelvic infiltrative features ( fig . 2 ) . however , the mucosal surfaces of the renal pelvis , ureter and calyces were smooth , and there was no evidence of urothelial malignancy . additionally , the mucosal layers of the renal pelvis , calyces and ureter were intact without abnormal urothelial changes . microscopically , the tumor occupying the renal sinus contained widely scattered , hyperplastic lymphoid follicles , characteristic of a lymphoproliferative lesion . the follicles varied in size and showed polarized germinal centers ; moreover , interfollicular spaces were markedly infiltrated by mature plasma cells , highlighted by cd138 immunostaining ( fig . 3 ) . immunostaining for  and  immunoglobulin light chains indicated that the plasma cells were polyclonal in origin . immunostaining for human herpes virus 8 ( hhv-8 ) was performed , the results of which were negative . these histological and immunohistochemical findings were compatible with a diagnosis of castleman 's disease of the plasma cell type . three months after the operation , there was no evidence of disease recurrence on follow - up abdominal ct . the occurrence of castleman 's disease in the renal sinus is exceedingly rare.1 to the best of our knowledge , only a few cases have been reported.1,3 - 6 the clinicopathological characteristics of the reported cases , involving six males and one female , are summarized in table 1 . although castleman 's disease generally shows no gender preference,2 cases involving the renal sinus appeared to show a male predominance . the median age for castleman 's disease is in the fourth decade.2 however , the mean age of the cases involving the renal sinus was 65 years . the main presenting symptoms included abdominal pain , weight loss , anorexia , and microscopic hematuria . five cases were of the plasma cell type , one of the hyaline vascular type and one of mixed type . the patient in the present case , a 64-year - old male , presented with symptoms of microscopic hematuria , and his disease was histologically classified as plasma cell type and clinically as unicentric type . although the exact pathophysiology of castleman 's disease is unknown , recent reports suggest that hhv-8 infection may stimulate b lymphocytes to induce interleukin 6 ( il-6 ) production in the mantle zone ; il-6 overproduction has been shown to be associated with the systemic manifestations of castleman 's disease , especially in cases of multicentric disease.7 in our case , immunostaining for hhv-8 was performed , but the result was negative . preoperative diagnostic imaging methods are not useful in differentiating castleman 's disease arising in the renal sinus from other diseases because of a lack of tumor - specific imaging features . previously , nishie et al.1 described the ct and magnetic resonance imaging features of three cases of castleman 's disease involving the renal sinus . they reported that the renal sinus lesions formed in castleman 's disease can appear as homogeneous masses with mild enhancement , such as is often observed in malignant lymphomas . thus , it is difficult , on the basis of radiological findings , to differentiate castleman 's disease from malignant lymphomas infiltrating the renal sinus . other differential diagnoses may include invasive urothelial carcinoma , granulomatous diseases , sarcomas , and metastases . consequently , pathological evaluation is currently the only method of identifying castleman 's disease of the renal sinus . here we have described an extremely rare case of unicentric castleman 's disease of the plasma cell type arising in the renal sinus . although preoperative diagnosis of castleman 's disease is difficult and accurate diagnosis is only possible by histopathologic evaluation , it should be considered in the differential diagnosis of renal sinus tumors .
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 .