Teaching Case

A 61-year-old female patient. Presenting signs: haematuria. Risk factors: non-smoker, no family history, non-occupational exposure to amines, recurrent infectious cystitis.

Previous examination: cytology negative for neoplastic cells and cystoscopy negative for masses.

Past medical history: congenital left-renal aplasia, no concomitant pathologies.

Renal encapsulated solid mass (36 mm in maximum diameter) at the level of the lateral mid-third of the right kidney. The mass shows post-contrast enhancement lower than the surrounding tissue, at the late arterial phase (HU 57). At the nephrographic (HU 77) and excretory phase (HU 147), the tumour shows no significant contrast wash-out. At the level of the renal pelvis there is a tiny filling defect visible on the nephrographic phase. Area of altered tissue perfusion at the level of the superior pole, visible on the coronal plane. No hydronephrosis was detected.

Background: Collecting duct carcinoma is an extremely rare condition, accounting for 0.4–1.8% of all RCCs [1]. This tumour is most prevalent among men older than 50 years (M>F) [2], differing from medullary carcinoma, which is mostly frequent among men younger than 25 years (3:1 male preponderance) [3]. Most CDC are clinically aggressive tumours often presenting at an advanced stage with a poor prognosis [4]. CDC might be similar to urothelial carcinoma and its radiologic and pathologic findings differ from those of other RCCs. [5]

Clinical Perspective: Common presenting symptoms are gross haematuria and flank pain following the nephrosis given by the mass effect and general weakness. CDC is also found with a palpable abdominal mass on physical examination. The diagnostic work-up is usually initiated with urine cytology followed by selective lavage and cystoscopic brush biopsies. CT scans or MR imaging are required to evaluate the renal parenchyma and to stage the disease.

Imaging Perspective: On CT urography (CTU), a multiphasic helical protocol is  preferred to split bolus technique, which might be used to lower radiation exposure. It consists of a pre-contrast scan followed by a late arterial, early corticomedullary phase scan, a nephrographic phase and an excretory scan [6]. CDC often shows infiltrative growth, which differs from the typical expansile pattern of growth exhibited by most renal malignancies [7]. At CT, the mass appears hypoattenuating and hypovascular. Calcification is seen in up to 25% of patients. Apart from CTU, MR urography is a useful diagnostic procedure for staging purposes. Imaging findings that suggest the diagnosis of collecting duct carcinoma include a medullary epicenter and low-signal intensity on T2-weighted MR images [3].

Outcome: No standard therapy for CDC has been established. Therapeutic options may include surgery to remove the kidney, chemotherapy with gemcitabine and cisplatin and immunotherapy [4].

Take Home Message / Teaching Points:

1. CDC might be similar to urothelial/medullary carcinoma and its radiologic and pathologic findings differ from those of other RCCs [5].
2. Post-contrast enhancement is usually less conspicuous and late than RCC, however both can show early enhancement and de-enhancement.
3. CDC origin from the collecting duct is usually suggested by its medullary location.