| Pearls | - UTUCs have an estimated incidence of 2 cases per 100,000 population in developed countries and are increasingly found incidentally. They comprise 5–7% of all UC and less than 10% of all renal tumors. They are mostly seen in patients older than 60 years (mean age of 73) and are 2–3 times more common in males as opposed to females. Significant risk factors include tobacco and smoking, alcohol, occupational carcinogens (e.g., aniline dyes), medication toxicity (e.g., cyclophosphamide), and known history of UC . Up to 2/3 of UTUCs develop in the renal pelvis, making it the second most common site for UC after the bladder. Multifocal in nature, up to 50% of patients with a UTUC develop a metachronous bladder UC and up to 4% of patients with a bladder UC develop a metachronous UTUC
- CTU is the standard imaging modality as recommended by the American College of Radiology (ACR) Appropriateness Criteria and American Urological Association (AUA) guidelines for adult patients who present with hematuria. Phases in renal imaging include noncontrast, corticomedullary (intense enhancement of the cortex) or arterial phase, nephrogenic (enhancement across the renal parenchyma) or venous phase, and excretory or delayed phase. The CTU protocol at least includes non-contrast, nephrographic, and excretory phases, which ensure optimal visualization of the renal parenchyma, collecting system, and any potential urothelial abnormalities. Ideally, we want to maximize the distension and opacification of the urinary tract during the excretory phase, which is crucial for detecting lesions such as urothelial thickening, focal filling defects, and mass-forming tumors.
- For image acquisition, we use dual-source MDCT scanners Following noncontrast imaging, a single bolus of 100–120 mL of intravenous (IV) contrast (Omnipaque, 350 mg/mL) is peripherally injected at 4–5 mL/s. Arterial (corticomedullary) phase imaging is acquired 30–35 s postinjection using bolus tracking at the abdominal aorta, followed by venous (nephrogenic) phase at 60–70 s, and delayed (excretory) phase at 5–8 min. Using a soft-tissue kernel and slice thickness of 0.75 mm at 0.5 mm intervals and collimation at 128 Å~ 0.6 mm, multiplanar reconstructions (MPR) in coronal and sagittal planes are generated after standard axial image acquisition. In a split-bolus protocol, contrast is administered at two intervals 5 min apart and a combined nephrogenic and excretory phase is imaged at around 7 min. Although it does lower radiation exposure, because a fraction of the contrast is excreted at a time, the collecting system may not achieve optimal distension.
- An optimized multiphase CTU protocol, including a corticomedullary phase, achieves a pooled sensitivity of 92% (CI 0.85–0.96) and specificity of 95% (CI 0.88–0.98) for detecting UTUC. However, other lesions that mimic UTUC or vice versa can be challenging. Sensitivity decreases to 89% for lesions < 5 mm and 40% for lesions < 3 mm, with sessile (flat) type lesions even more difficult to diagnose [4]. Smaller intraluminal neoplasms are obscured by dense contrast in the renal collecting system with standard soft-tissue window settings, so use of wide window settings can help increase detection (i.e. window level 50, window width 500). Other techniques to maximize distension of renal collecting system include oral or intravenous hydration, which improve distention and dilutes contrast. Typically, 500–1000 mL of water per oral prior to the study at our institution.
- UTUC presents with a variety of classical imaging patterns on CTU, ranging from subtle urothelial thickening to large, infiltrative masses. Early signs include smooth or nodular thickening along the renal collecting system or ureters, which become visible during nephrographic phase as enhancing lesion and excretory phase as filling defects or irregular luminal narrowing (Missing the calyx in excretory phase, often described as an “amputated calyx,” reflects tumor invasion in the calyx, while focal dilatation of calyces without smooth contours may also signal malignancy These findings highlight the importance of contrast-enhanced CT for detecting even low-grade lesions.
- Xanthogranulomatous pyelonephritis, chronic infection such as tuberculosis, and intraluminal blood clots and fungus balls, as well as other neoplasms such RCC, oncocytic neoplasm, lymphoma, and metastases can mimic UTUCs on CTU. Notably, benign entities like blood clots, sloughed papillae, and fungus balls remain intraluminal and lack attachment to the urothelial wall. Their absence of enhancement on post-contrast imaging further helps distinguish them from UTUCs, which may show enhancement and adherence to surrounding tissues. Similarly, fibrosis and chronic inflammation can appear deceptively neoplastic. Other benign identities that can be radiologically indistinguishable include polyureteritis cystica and malacoplakia that cam mimic multifocal UTUC. Squamous cell carcinoma (SCC), although not as common in Western countries, is another mimicker of UTUC on imaging and should be a consideration in patients from regions where schistosomiasis is prevalent.
- Accurate diagnosis and staging of upper tract urothelial carcinoma in patients presenting with hematuria in the ED requires a combination of optimized imaging protocols, including CTU and advanced 3D postprocessing, as well as clinical correlation. While multidetector CT urography remains the cornerstone of evaluation, awareness of imaging pitfalls and mimics is essential to prevent diagnostic errors. Use of correct and optimal scan protocols can strongly impact the diagnostic accuracy, and it is essential to ensure this consistently to be certain that a diagnosis will be made in a timely fashion. Tailoring the imaging strategy to patient presentation and leveraging postprocessing tools improves diagnostic precision and outcomes in UTUC management..
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