Severe ureteral obstruction secondary to an upper urinary tract urothelial carcinoma

A 55-year-old female patient, suffering from hematuria for the past few weeks, came to the hospital for a check-up. An ultrasound examination revealed a dilatation of the left renal calyces and pelvis, however, could not report upon the cause. A urine cytology analysis did not prove urothelial carcinoma (UC), and the patient reported no other significant symptoms. A contrast CT examination was requested for further evaluation.

CT images, with spectral reconstructions, showed dilated left renal calyces and pelvis which were hyperdense in the Virtual Non-Contrast (VNC) images, suggesting blood content (Fig. 1). Two small lesions, measuring 6 x 5 mm in the central part of the renal pelvis and 4 x 5 mm at the pelviureteric junction, were visualized in the Monoenergenetic Plus images displayed at 45 keV, as well as in the iodine maps fused with VNC. Both lesions were not visible in standard CT images (Monoenegetic images displayed at 70 keV, corresponding to images acquired at 120 kV), presumably due to their small size and being obscured by the hyperdense blood content. The small lesion at the pelviureteric junction could most probably be considered as a discrete tumor infiltration and the cause of a severe ureteral obstruction (Figs. 2 & 3). A delayed scan, performed 4 hours later, showed no excretion of contrast agent (Fig. 4). Subsequently, an ureteroscopy was performed and the histological results confirmed the diagnosis of an UC. The patient was then scheduled for surgery.

Fig. 2: Coronal images show a small lesion in the central part of the left renal pelvis, unidentifiable in a standard image (Fig. 2a), but significantly enhanced and clearly visible in a Monoenergetic Plus image displayed at 45 keV (Fig. 2b, arrow) and an iodine map fused with VNC (Fig. 2c, arrow).

Fig. 4: A VRT image from a delayed scan (4 hours later) shows no excretion of the left kidney due to a severe obstruction at the pelviureteric junction.

Urothelial tumors affecting the upper urinary tract are relatively rare, accounting for only approximately 1% of all urothelial tumors. The most common histological type is UC found in 90% of the cases. It can cause ureteral obstruction leading to hydronephrosis, infection or spontaneous rupture. Traditionally, a CT evaluation for hematuria with suspected UC would require both non-contrast and contrast scans. [1] In this case, only one contrast scan is performed, acquiring spectral CT data which can be used for further spectral reconstructions, such as VNC, Monoenergetic Plus and iodine maps. The blood content in the renal pelvis is identified in the VNC images and the proportion of the bleeding to the renal pelvis can also be determined. Both lesions, especially the tiny discrete infiltration at the pelviureteric junction causing severe ureteral obstruction, are not visible and could have been missed in standard CT images. However, they are significantly enhanced and clearly visible in the Monoenergetic Plus images displayed at 45 keV as well as in the iodine maps fused with VNC images. This case is performed with NAEOTOM Alpha, a newly developed CT scanner with photon-counting detectors. It provides energy-resolved CT data with a very high spatial resolution, without electronic noise. [2] One of the key benefits of photon-counting CT is the availability of spectral CT data in any scan, without having to consider and decide on the type of the scan before data acquisition or to recall the patient after scanning. This has a major impact on improving clinical routine practice and helping the physicians make confident diagnoses.