- The ureter is a muscular tube 25-30 cm in length that begins at the ureteropelvic junction (UPJ) and courses entirely in the retroperitoneum to the bladder. The proximal portion lies anterior to the psoas muscle and runs along with the gonadal vein. The mid portion of the ureter enters the pelvis as it crosses anterior to the iliac vessels. Distally, the ureter courses inferiorly and laterally along the pelvic sidewalls before taking an abrupt turn medially to enter the bladder at the ureterovesical junction (UVJ). The ureter passes through the bladder wall obliquely, creating a valve effect to prevent reflux.
- Normal imaging findings include kinking and tortuosity of the proximal ureter. Normal anatomic narrowings are encountered at the UPJ, where the ureter crosses the iliac vessels, and at the UVJ. Undulations and narrowings from peristalsis are common.
Imaging Techniques and Indications
- IVP has been largely abandoned in the United States and replaced with CTU given higher accuracy for renal and ureteral disease.
- US rarely identifies the normal ureter due to its small size and deep retroperitoneal course surrounded by echogenic fat and bowel. Generally, only a dilated ureter may be visualized for part or all of its length to the bladder. When US identifies hydronephrosis, it is important to carefully evaluate the UVJ, as US frequently detects obstructing stones as an echogenic, shadowing lesion with twinkle artifact.
- CT urography (CTU) is commonly performed to work-up hematuria (gross and microscopic), ureter trauma, strictures, and other diseases. Because microscopic hematuria is a common complaint and often benign, the American Urologic Association recently updated their guidelines, establishing 3 risk groups for patients with microscopic hematuria; only those in the high-risk group should undergo CTU, while patients in the other groups should only be imaged with renal US.
- There are many ways to perform CTU. The minimum exam consists of NECT, to look for stones, followed by CECT in the delayed phase, to opacify the ureters and bladder. Most institutions also image the kidneys and ureters in the nephrographic (&/or corticomedullary) phase to increase the sensitivity for renal cell carcinoma and urothelial carcinoma (UC), as small urothelial masses enhance and can be readily detected on these earlier phases.
- Split bolus techniques combine early and delayed phases into one scan and are commonly employed to decrease radiation doses. Various maneuvers such as IV hydration and Lasix administration are used at some institutions to better opacify the ureters but add complexity with minimal benefit and are not widely adopted. Perhaps the easiest and safest is oral hydration prior to the scan with 1 L of water.
- Unopacified segments of ureter are commonly encountered at CTU. Historically, this was felt to be a problem as disease in this segment could not be ruled out. However, with accumulated experience and data, it is clear that UC is not underdiagnosed in unopacified segments, and repeat imaging is of little benefit.
- Therefore, if unopacified segments are encountered, the ureter should still be carefully evaluated for any focal mass, enhancement, or abrupt change in caliper as this could indicate malignancy.
- Minor changes in ureter caliber are normal and a part of peristalsis; the ureter wall remains thin and does not show focal enhancement.
- MR urography (MRU) can show the ureters well through both heavily T2-weighted imaging (similar to MRCP) and dynamic contrast imaging. The advantage is higher temporal resolution, but the spatial resolution is less than CTU. MRU is also a technically more challenging study, often requiring bladder catheterization, IV or oral hydration, and IV Lasix administration. Younger pediatric patients are often sedated for the procedure.
- Because of this, the main indication for MRU is evaluation of congenital anomalies in a child. MRU sensitivity for UC is slightly less than CTU, and therefore CTU is the preferred modality in adults at most institutions.
- MRU however does have the added benefit of being able to perform renal function quantitative measurements similar to nuclear medicine renal scans.
- Retrograde pyelography is often performed by the urologist through a cystoscope after cannulating the ureteral orifice. Antegrade pyelography can be performed by injection of contrast after placement of a nephrostomy tube. Both serve an important diagnostic role to further investigate abnormal findings on CT or MR, and these techniques also have the added benefit of biopsy or intervention to be performed simultaneously.
Approach to Ureter
- Ureter pathology should always be suspected when hydronephrosis is detected. The ureter should be carefully followed to look for the point of obstruction, which is often identified as an abrupt change in caliber, wall thickening/mass, or intraluminal filling defect. By far and away, the most common obstructing pathology is a stone. Stones can become lodged anywhere along the ureter but most commonly are found at the UVJ followed by the UPJ. In patients with cancer, malignant obstruction is not uncommon. This may occur either due to extrinsic mass effect upon the ureter, encasement or invasion by a retroperitoneal mass, or (less commonly) from metastasis to the ureter.
- Malignant obstruction also occurs due to primary UC of the ureter. The ureter is the least commonly involved part of the urinary tract, and the distal ureter is the most common location of UC.
- Less common etiologies of ureter strictures include iatrogenic (often from stone treatments, GYN surgery), crossing vessels, endometriosis, infection (TB/schistosomiasis), and benign masses (IgG4, malakoplakia, fibroepithelial polyp).
- Congenital anomalies of the ureter are common with partial duplication (bifid ureter) frequently seen incidentally in adults. Complete ureter duplication and ureterocele is commonly diagnosed in childhood but may present in adults.
- Dilated, nonobstructed ureters are commonly encountered (90% in the 3rd trimester of pregnancy). When patients are symptomatic, imaging for stones may be necessary.
- Barocas DA et al: Microhematuria: AUA/SUFU buideline. J Urol. 204(4):778-86, 2020
- Raman SP et al: Upper and lower tract urothelial imaging using computed tomography urography. Urol Clin North Am. 45(3):389-405, 2018
- Potenta SE et al: CT urography for evaluation of the ureter. Radiographics. 140209, 2015
- Silverman SG et al: What is the current role of CT urography and MR urography in the evaluation of the urinary tract? Radiology. 250(2):309-23, 2009
- Grattan-Smith JD et al: MR urography in children: how we do it. Pediatr Radiol. 38 Suppl 1:S3-17, 2008
- Van Der Molen AJ et al: CT urography: definition, indications and techniques. A guideline for clinical practice. Eur Radiol. 18(1):4-17, 2008
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