Magnetic resonance imaging in the evaluation of ureteropelvic junction obstructed kidney

Magnetic resonance imaging in the evaluation of pelvi-ureteric junction obstruction: an all-in-one approach

OBJECTIVE

To study the ability of comprehensive magnetic resonance imaging (MRI) to replace multiple imaging methods in the evaluation of patients with pelvi-ureteric junction obstruction (PUJO).

PATIENTS AND METHODS

Between May 2003 and November 2005, 46 consecutive patients (22 male and 24 females; mean age 31.6 years) with symptomatic primary PUJO were included. All had comprehensive MRI, including MR urography (MRU), dynamic MRI and MR angiography (MRA). Morphological results of MRU were compared with that of renal ultrasonography or intravenous urography, while the anatomical results of MRA were compared with the operative findings. A correlation between MR clearance and radioisotope clearance was done using linear regression analysis.

RESULTS

MRU showed the morphology of the collecting system in all patients, and the ureter below the PUJ in 31 of 46 (67%), but renal stones were missed in three of 10 patients. MRA showed crossing vessels in 22 patients (48%). There was a strong correlation between MR clearance and radioisotope clearance (r = 0.823, P < 0.001). From the MRI results, 35 patients (19 with crossing vessels and 16 with marked hydronephrosis) had pyeloplasty and 11 had an endopyelotomy. Findings during pyeloplasty showed one false-negative and one false-positive result of the preoperative MRI. Therefore, the sensitivity, specificity and accuracy of MRA were 95%, 94% and 94%, respectively. The outcome was successful in 44 (96%) patients. One failure after pyeloplasty was managed with endopyelotomy and the other was treated with pyeloplasty after endopyelotomy.

CONCLUSION

Comprehensive MRI is a valuable and accurate single-imaging method for evaluating patients with PUJO.

Contrast-enhanced magnetic resonance angiography for the detection of crossing renal vessels in children with symptomatic ureteropelvic junction obstruction: comparison with operative findings

BACKGROUND

Crossing renal vessels (CRV) are associated with ureteropelvic junction (UPJ) obstruction, particularly when presentation is beyond the neonatal period. Their presence may influence surgical management.

OBJECTIVE

To evaluate the accuracy of contrast-enhanced magnetic resonance angiography (CE-MRA) in the identification of CRV in children requiring surgical treatment of symptomatic UPJ obstruction, against a gold standard of laparoscopic or open surgical findings.

MATERIALS AND METHODS

We reviewed CE-MRA studies (3-D T2-weighted turbo spin-echo and multiphase 3-D spoiled gradient echo following intravenous gadolinium administration) of 14 children, age range 6-15 years, performed prior to surgery for suspected CRV-related UPJ obstruction. Consensus reviews of the CE-MRA studies were compared with surgical findings.

RESULTS

CE-MRA demonstrated CRV at the level of the obstruction in nine and no crossing vessels in five children. These were all verified intraoperatively (chi2=14.0; P<0.001). In eight of the nine patients with CRV there was no evidence of intrinsic obstruction at surgery. In the remaining patient there was fibrosis of the upper ureter.

CONCLUSION

CE-MRA is an accurate means of identifying CRV in children older than 6 years with symptomatic UPJ obstruction.

Functional MRI of the kidney: tools for translational studies of pathophysiology of renal disease

Magnetic resonance imaging (MRI) provides exquisite anatomic detail of various organs and is capable of providing additional functional information. This combination allows for comprehensive diagnostic evaluation of pathologies such as ischemic renal disease. Noninvasive MRI techniques could facilitate translation of many studies performed in controlled animal models using technologies that are invasive to humans. Such a translation is being recognized as essential because many proposed interventions and drugs that prove efficacious in animal models fail to do so in humans. In this article, we review the state-of-the-art functional MRI technique as applied to the kidneys.

Role of multiphasic helical computed tomography in planning surgical treatment for pelvi-ureteric junction obstruction

OBJECTIVE

To evaluate the role of multiphasic helical computed tomography (CT) in planning surgical treatment for pelvi-ureteric junction obstruction (PUJO).

PATIENTS AND METHODS

Multiphasic helical CT was used in 60 consecutive patients (mean age 32 years, sd 13.72) with primary PUJO. The different images were interpreted before surgery by a urologist and radiologist. The number, type and relation of the crossing vessels to the PUJ were detected. Pyeloplasty (open or laparoscopic) was used in patients where there was a significant crossing vessel (i.e. > 2 mm in diameter and passing at the PUJ) or with ballooning of the renal pelvis. Endopyelotomy (antegrade or retrograde) was used in the other patients. Subjective and objective success rates were determined 3-6 months after treatment and then every 6 months.

RESULTS

Hyperdense renal stones were detected in precontrast images in 15 patients, significant crossing vessels in 33 (55%), and anterior malrotation of the renal pelvis in 23 (38%; 19 associated with significant crossing vessels, i.e. ureterovascular hydronephrosis). A large para-pelvic cyst compressing the PUJ and upper ureter was detected in one patient. Pyeloplasty was used in 45 patients, among whom the sensitivity of multiphasic helical CT in detecting crossing vessels was 97%, the specificity 92% and accuracy 96%. Uncomplicated endopyelotomy was used in 14 patients and percutaneous aspiration of the para-pelvic cyst in one.

CONCLUSION

Multiphasic helical CT can accurately delineate the spatial anatomy of the renal and peri-renal area; it may be important in planning surgical treatment for PUJO, especially when endopyelotomy is considered.

Radiologic evaluations affecting surgical technique in ureteropelvic junction obstruction

Ureteropelvic junction obstructions can be explored by radiographic methods including ultrasonography, intravenous pyelography, radionuclide scanning, magnetic resonance imaging and computerized tomography. The decision to operate on an ureteropelvic stricture is best given by the results of a radionuclide scan, which can demonstrate the obstruction. The operative technique is influenced by the presence of a polar artery, as this presence represents a danger when endopyelotomy is performed. The presence of a polar artery may be demonstrated by computerized tomography using helicoidal reconstruction. Magnetic resonance imaging with injection of gadolinium is also useful when available. The outcome and the results of the surgical procedure are also evaluated by radionuclide scanning.

Captopril MR renography in a swine model: toward a comprehensive evaluation of renal arterial stenosis

PURPOSE

To test the feasibility of captopril magnetic resonance (MR) renography and to validate the technique in an animal model of renal arterial stenosis.

MATERIALS AND METHODS

Seven pigs with induced renal arterial stenosis were studied. MR renography was performed with a T1-weighted approach by using three-dimensional fast imaging with steady-state precession, or FISP, sequences after administration of a bolus of 0.1 mmol of gadopentetate dimeglumine per kilogram of body weight. Captopril was administered to improve the specificity.

RESULTS

The results demonstrate that differences in renographic curves and indices are observed only if an anatomically substantial stenosis, typically a diameter reduction of more than 70%, is present and captopril is administered.

CONCLUSION

In this preliminary experience in an animal model, captopril MR renography provided data consistent with expectations based on conventional renographic results.

Ureteropelvic junction obstruction: use of helical CT for preoperative assessment--comparison with intraarterial angiography

PURPOSE

To evaluate helical computed tomography (CT) in the preoperative assessment of crossing arteries in kidneys with ureteropelvic junction (UPJ) obstruction and to compare the results with those obtained by means of angiography.

MATERIALS AND METHODS

Forty-one consecutive patients with symptomatic UPJ obstruction in 42 obstructed kidneys underwent renal helical CT and renal intraarterial digital subtraction angiography (DSA; flush aortography and bilateral selective renal injections). The helical CT and DSA images were interpreted in a blinded manner by two readers, and the results were compared.

RESULTS

DSA showed 126 renal arteries in the 41 patients; 56% of patients had supernumerary renal arteries. Helical CT depicted 121 (96%) of these 126 renal arteries prospectively. Retrospectively, 124 (98%) renal arteries were visible on CT images. Twelve (29%) of the 42 kidneys with UPJ obstruction had identifiable arteries crossing the UPJ on DSA images. If DSA is used as the standard of reference, CT angiography was 100% sensitive and 96.6% specific for depicting these crossing arteries.

CONCLUSION

Renal helical CT seems suitable to replace intraarterial DSA in the preoperative assessment of crossing arteries in kidneys with UPJ obstruction.

Functional imaging of the kidneys with fast MRI techniques

Availability of faster and stronger gradient systems have given rise to a multitude of fast MRI data acquisition strategies which have tremendously increased the scope of MRI applications. These have led to the realization of long desired comprehensive approaches to evaluate anatomy and function using a single modality. In this work, we describe some of our own experiences with functional evaluation of the kidneys using MRI. Examples that suggest the feasibility of comprehensive approaches for evaluation of renal disease are also provided. We also introduce BOLD renal MRI, a method that may allow basic understanding of human renal physiology and pathophysiology in a way that has not been previously possible.