Abstract
Collecting duct carcinoma, also known as Bellini duct carcinoma, is a renal tumor with poor prognosis that accounts for only 1% of all renal cancers. We encountered a rare case of collecting duct carcinoma infiltrating into the entire right kidney. The patient was a man in his 60s. Abdominal ultrasonography demonstrated an enlarged right kidney, which appeared to be occupied by a tumor with poorly defined margins. The central echo complex of the kidney appeared extremely narrow due to tumor growth. However, the reniform shape was relatively well-preserved despite the large size of the tumor. Tumor echogenicity was almost isoechoic when compared with the cortex of the normal left kidney. Doppler imaging demonstrated that the tumor was scarcely fed by the tumor vessels. To the best of our knowledge, no previous reports have precisely described sonographic features of collecting duct carcinoma. Although 63 reports have been published in Japan since 1988, most have described only the findings from computed tomography and/or pathological examination. According to this literature, preservation of a reniform shape was found in 72% (21/29) of cases, and tumor hypovascularity was evident in 96% (52/54). On the other hand, diffuse infiltrating growth into the entire kidney, as in the present case, was seen in only 11% (7/62). Considering these past reports and the findings in the present case, sonography of collecting duct carcinoma could show the following features: 1) infiltrative growth; 2) preservation of reniform shape irrespective of tumor size; 3) deformity or narrowing of the central echo complex due to tumor growth; 4) hypovascularity on Doppler imaging; and 5) non-characteristic echogenicity depending on individual cases. When such imaging findings are apparent on sonography, collecting duct carcinoma should be included among the differential diagnoses.
