Magnetic resonance urography

Update on MR urography (MRU): technique and clinical applications

Magnetic resonance imaging of the upper tract (pyelocalyces and ureters) or MR Urography (MRU) is technically possible and when performed correctly offers similar visualization of the upper tracts and for detection of non-calculous diseases of the collecting system similar specificity but with lower sensitivity compared to CTU. MRU provides the ability to simultaneously image the kidneys and urinary bladder with improved soft tissue resolution, better tissue characterization and when combined with assessment of the upper tract, a comprehensive examination of the urinary system. MRU requires meticulous attention to technical details and is a longer more demanding examination compared to CTU. Advances in MR imaging techniques including: parallel imaging, free-breathing motion compensation techniques and compressed sensing can dramatically shorten examination times and improve image quality and patient tolerance for the exam. This review article discusses updates in the MRU technique, summarizes clinical indications and opportunities for MRU in clinical practice and reviews advantages and disadvantages of MRU compared to CTU.

ACR Appropriateness Criteria® Acute Pyelonephritis

Pyelonephritis refers to infection involving the renal parenchyma and renal pelvis. In most patients, uncomplicated pyelonephritis is diagnosed clinically and responds quickly to appropriate antibiotic treatment. If treatment is delayed, the patient is immunocompromised, or for other reasons, microabscesses that form during the acute phase of pyelonephritis may coalesce, forming a renal abscess. Patients with underlying diabetes are more vulnerable to complications, including emphysematous pyelonephritis in addition to abscess formation. Additionally, diabetics may not have the typical flank tenderness that helps to differentiate pyelonephritis from a lower urinary tract infection. Additional high-risk populations may include those with anatomic abnormalities of the urinary tract, vesicoureteral reflux, obstruction, pregnancy, nosocomial infection, or infection by treatment-resistant pathogens. Treatment goals include symptom relief, elimination of infection to avoid renal damage, and identification of predisposing factors to avoid future recurrences. The primary imaging modalities used in patients with pyelonephritis are CT, MRI, and ultrasound. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Tumors of Renal Collecting Systems, Renal Pelvis, and Ureters: Role of MR Imaging and MR Urography Versus Computed Tomography Urography

Hematuria evaluation remains a common problem, particularly in patients who smoke and are at risk for urothelial tumors. Lifetime surveillance of the urothelium is often required once urothelial cancer is diagnosed. Computed tomography urography (CTU) has exquisite sensitivity and specificity for identification of renal and urothelial lesions. The examination is well accepted by patients and physicians. Possible harms include radiation exposure and contrast-induced nephropathy. MR imaging is also an accurate test, but requires longer exam times, and may not demonstrate stones. We present the technical and interpretation skills required to use MR urography and CTU effectively.

Magnetic resonance urography in the pediatric population: a clinical perspective

Diagnostic imaging in pediatric urology has traditionally relied upon multiple modalities based on availability, use of ionizing radiation, and invasiveness to evaluate urological anomalies. These modalities include ultrasonography, voiding cystourethrography, fluoroscopy and radionuclide scintigraphy. Magnetic resonance urography (MRU) has become increasingly useful in depicting more detailed abdominal and pelvic anatomy, specifically in duplex collecting systems, ectopic ureter, ureteropelvic junction (UPJ) obstruction, megaureter and congenital pelvic anomalies. Here we discuss the clinical role of MRU in the pediatric population and its future direction.

MR urography (MRU) of non-dilated ureter with diuretic administration: Static fluid 2D FSE T2-weighted versus 3D gadolinium T1-weighted GE excretory MR

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T2w-MRU with multiple orientations and diuretic is sufficient to identify non-dilated ureter.

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T2w-MRU offers information on ureteral contractions and could be proposed to detect initial obstruction before hydronephrosis occurs (for instance in cases of endometriosis).

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T2w-MRU could also be used to evaluate potential renal donors or in patients unable to receive gadolinium.

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CE-MRU rapidly produces an overdistended bladder with a risk of false positive diagnosis of mild obstruction.

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CE-MRU is less convenient for patients.

Objective

The goal of this prospective study was to compare the efficiency of two types of MRU after diuretic administration to identify the non-dilated ureter.

Methods

MR pelvic examinations were performed in 126 patients after receiving furosemide. Each patient underwent in addition to their protocol for context, two types of MRU: 2D T2-weighted FSE (T2w-MRU) and 3D Gd T1-weighted GE (CE-MRU). Four segments were checked for each ureter.

For the first part of the analysis, readers evaluated the whole image quality using a four points subjective scale and for the second part, they were asked to score separately each ureteral segment as present or absent.

Results

1008 ureteral segments were checked. For the image quality, readers did not find any significant difference (3.8 ± 0.5 vs 3.6 ± 0.7, p value: 0.13) between MRU methods. The interobserver agreement was excellent with a κ correlation coefficient as high as 0.89 for T2w-MRU and 0.92 for CE-MRU, respectively.

For the detection of the segments and considering the 9 rotations for the T2W MRU, there were no statistically significant differences between the two groups.

Conclusion

T2-weighted MRU with multiple orientations and diuretic is sufficient to identify the non-dilated ureter. It offers information on ureteral peristaltism. It can be suggested that this sequence is able to detect an initial obstruction before hydronephrosis occurs.

Diagnostic value of combined static-excretory MR Urography in children with hydronephrosis

The aim of this study was to determine the feasibility, accuracy and diagnostic potential of combined static-excretory MR Urography in children with sonographically detected hydronephrosis. We prospectively evaluated 28 children (11 girls and 17 boys), mean age 8.3 years (range 2 months–16 years). Static-excretory MR Urography was performed in all cases. The results of MR Urography were compared with the results of other imaging modalities, cystoscopy and surgery. In 28 children, 61 renal units were evaluated by MR Urography (the renal unit is the kidney and its draining ureter). The final diagnoses included: normal renal units (n = 23); uretropelvic junction obstruction (n = 14); megaureter (n = 8); midureteric stricture (n = 1), complicated duplicated systems (n = 5), post ESWL non-obstructive dilation (n = 2), extrarenal pelvis (n = 4), dysplastic kidney (n = 4). Complex pathology and more than one disease entity in were found in 7 children. The MRI diagnosis correlated with the final diagnosis in 57 units, with diagnostic accuracy 93.4%. In conclusions static and excretory MRU give both morphological and functional information in a single examination without exposure to ionizing radiation and iodinated contrast agent. It is a valuable imaging technique for children with upper urinary tract dilatation; especially in cases of complex congenital pathologies and severely hydronephrotic kidney.

Collecting duct carcinoma of the kidney: Imaging observations of a rare tumor

Collecting duct carcinoma (CDC) is a rare type of renal neoplasm. Early diagnosis is possibly the only factor leading to a prolonged survival for patients with CDC. The purpose of the present study was to characterize the imaging features of CDC and improve its diagnosis. Radiological data of six patients were retrospectively reviewed by three experienced radiologists, including six cases examined with non-contrast computed tomography (CT) scans, five with contrast-enhanced CT scans, one with magnetic resonance urography, one with renal dynamic imaging and two with conventional whole-body ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT scans. All patients were pathologically confirmed with CDC. In total, seven tumors were detected in the six cases, with a mean size of 5.3 cm. Of the tumors, two were solid and the rest were complex solid and cystic. In addition, six tumors were located in medullary areas and only one tumor was found in the cortical location. Cystic components were observed in five tumors. Weak enhancements were observed in all six tumors examined with contrast-enhanced CT, and heterogeneous enhancements were also observed in the majority of these tumors with the exception of one tumor. Infiltrative growth and expansible growth were found in five and two tumors, respectively. Metastatic lesions were detected in all six patients. On MR urography, the involved kidney exhibited similar imaging observations to the CT scan. Renal dynamic imaging revealed a decreased renal function in the involved kidney and an increased renal function in the contralateral kidney. On PET/CT imaging, a marked uptake of ¹⁸F-FDG was found in primary and metastatic lesions. The results of the present study indicated that medullary location, weak and heterogeneous enhancement, infiltrative growth, damage of renal function in the involved kidney and a marked uptake of ¹⁸F-FDG are imaging observations commonly identified in patients with CDC. When a renal tumor exhibits these imaging features, CDC may be suggested as a valuable differential diagnosis.

Appearances of the circumcaval ureter on excretory urography and MR urography: A single-center case series

Objectives:

To describe Magnetic Resonance Urography (MRU) appearances of the circumcaval ureter, a rare congenital cause of hydronephrosis.

Materials and Methods:

Seven cases of circumcaval ureter, suspected on intravenous urography (IVU), underwent subsequent static MRU using heavily T2-weighted sequences.

Results:

The various appearances of circumcaval ureter on IVU and MRU were studied and compared. The circumcaval portion of the ureter was especially well seen on axial MRU sections, though this portion was routinely not visualized on IVU. In one case with a ureteric calculus, MRU also depicted a circumcaval course of the ureter, thus providing a complete diagnosis. In yet another case, where a circumcaval ureter was suspected on IVU, MRU proved the actual cause of ureteric obstruction to be a crossing vessel.

Conclusion:

Static MRU using heavily T2-weighted coronal and axial sequences can make or exclude the diagnosis of circumcaval ureter unequivocally.

The role of static magnetic resonance urography in the evaluation of obstructive uropathy

OBJECTIVE

To assess the diagnostic accuracy of static magnetic resonance urography (MRU) in hydronephrosis and to compare parameters of hydronephrosis in MRU with intravenous urography (IVU).

MATERIALS AND METHODS

Sixty-nine patients were included in this study of which 55 patients with a total of 63 hydronephrotic units underwent both IVU and MRU. MRU was performed on a 1.5 T scanner using heavily T2-weighted sequences. The level, grade, and cause of obstruction on each modality were interpreted by 2 radiologists. These were compared with the final diagnosis based on other appropriate modalities including imaging, intraoperative and histopathologic diagnosis.

RESULTS

The sensitivity and specificity MRU in detecting hydronephrosis were 95% and 100%, respectively. In determining the level of obstruction, the strength of agreement between IVU and MRU using kappa statistics was κ = 0.66, which corresponds to a good level of agreement. The Spearman correlation coefficient for the grade of hydronephrosis on MRU and IVU was 0.92 (95% confidence interval 0.86-0.95), with a P value of < .0001. The correct diagnosis was made in 89.2% of the cases by IVU and in 93.8% of the cases by MRU.

CONCLUSION

Along with a high sensitivity and specificity in detecting the presence, level, and grade of hydronephrosis, MRU without contrast also shows a good agreement with IVU. Static MRU can reliably replace IVU when the latter is contraindicated or technically difficult.

Contrast-material-enhanced MR urography in evaluation of postoperative lower urinary tract fistulae and leakages

Urinary fistulas and leakages of lower urinary tract are serious complications of various surgical procedures. Radiologists need to have enough information about these situations to perform precise diagnosis and treatment. Various techniques [such as intravenous pyelography, ultrasound, computed tomography (CT), CT urography, cystoscopy, cystography and magnetic resonance (MR) imaging] are used for the diagnosis of these conditions. Application of all these techniques reduces the comfort and cooperation of the patients and increases the cost. Here we present four postoperative patients with lower urinary tract fistula or leakage. To the best of our knowledge, there is no report regarding the use of contrast-material-enhanced MR urography (CE-MRU) in the demonstration of postoperative lower urinary tract fistulae and leakages. In conclusion, CE-MRU could show the existence and location of the urinary fistulae and leakages clearly without the need for another investigation technique, as described in our patients. Also, CE-MRU is a safe and relatively inexpensive technique that avoids exposure to radiation as well as nephrotoxic and more allergic contrast-material administration.

Magnetic resonance urography in duplex kidney with ectopic ureteral insertion

This is a report on the use of magnetic resonance urography (MRU) in a 6-year-old girl who presented with urinary incontinence. She had a left duplex kidney with poorly functioning upper moiety and ectopic insertion of the dilated upper pole ureter. MRU has been shown to be superior to conventional imaging techniques in delineating poorly functioning moieties of duplex kidneys and ectopic ureters.