Two small non-invasive papillary urothelial carcinomas in the left renal pelvis and ureter

A 76-year-old male patient, suffering from repeated episodes of renal colic associated with hematuria, had undergone two non-contrast CT scans to detect renal calculi; however, both were negative. Urine cytology analysis, to detect urothelial cancer, also resulted negatively. A contrast enhanced CT scan was requested and performed, in both the venous and late excretory phase, with a photon-counting CT (PCCT), NAEOTOM Alpha®, for further assessment.

CT images acquired in the venous phase revealed two small lesions, measuring 7 mm × 5 mm in size, in the left ureteropelvic junction and, 8 mm × 7 mm, in the left middle ureter. Both lesions were contrast enhanced. Using spectral reconstructions, the enhancement was clearly improved in the iodine maps and in the Monoenergetic Plus images displayed at 40 keV, compared to standard CT images (displayed at 70 keV, corresponding to images acquired at 120 kV). In the virtual non-contrast (VNC) images, both lesions appeared isodense. The left renal pelvis was dilated. No abnormalities, neither in the right renal pelvis and ureter nor in the bladder, were seen.

Subsequently, a low grade noninvasive papillary urothelial carcinoma (staging pTa, N0, M0) was histologically confirmed through biopsy and ureteroscopy. The patient underwent laser ablation of the tumors through cystoscopy, without adjuvant therapy recommended.

Fig. 2: A small lesion is shown in the middle ureter (arrows). The lesion appears isodense in the VNC image (Fig. 2a), slightly enhanced in standard CT image (Fig. 2b) and clearly enhanced in the Monoenergetic Plus image displayed at 40 keV (Fig. 2c) as well as in the iodine/ VNC fused image (Fig. 2d).

Urothelial carcinoma, also called transitional cell carcinoma, originates in the urothelial cells. It is the most common cancer of the renal pelvis or ureter, making up about 90% of all upper urinary tract tumors. If the cancer is confined to the urothelium, it is non-invasive and curable in more than 90% of the patients. If it has infiltrated into deeper layers of the urothelial wall, the likelihood of cure is 10–15%. In case it has infiltrated through the urothelial wall or distant metastases have occurred, it is usually incurable with available treatment. The depth of infiltration is a major prognostic factor at the time of diagnosis, therefore, a proper early diagnosis is relevant. In CT imaging, the identification and characterization of small lesions at an early stage require both high spatial resolution and optimal tissue contrasts, and ideally, not at the cost of radiation dose efficiency. This is technically very challenging.

PCCT provides energy-resolved CT data at increased spatial resolution without electronic noise and with improved tissue contrasts. [1] An electric field, instead of physical separation, is applied to define smaller sub-pixels which are read out separately to increase the spatial resolution. This approach also improves the geometrical dose efficiency of the detector. In this case, the entire range of the abdomen and pelvis is acquired with 0.4 mm slices at a radiation dose of only 7.2 mGy. The CNR is optimized due to a combination of missing down-weighting of the lower energy X-ray photons, the absence of the electronic noise and the inherent spectral information. CT data acquired in a contrast scan can then be used for further spectral reconstructions, such as virtual non-contrast (VNC) images, virtual monoenergetic images (Monoenergetic Plus) displayed at different keV levels, iodine maps and iodine/ VNC fused images. In fact, reading these different image types in daily practice is quite straightforward, as they can be interactively toggled, using Interactive Spectral Imaging (ISI) technique available with image viewing. As one of the key benefits of PCCT, spectral information is available in any scan. It is highly recommended to utilize this information in image reading for routine diagnosis.

As shown in this case, the identification and characterization of the two small enhancing lesions, only a few millimeters in size, benefit from the advantages provided by PCCT, helping the physicians make a confident diagnosis.