Magnetic resonance imaging in endourology

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.

Shockwave Lithotripsy: Anecdotes and Insights

Shockwave lithotripters have evolved considerably since the introduction of the Dornier HM3 machine 20 years ago. Although shockwave lithotripsy (SWL) remains the preferred treatment for the majority of symptomatic upper urinary-tract calculi, newer lithotripters are not as effective and may have a higher risk of side effects. Lack of progress in lithotripter evolution is attributable to inadequate understanding of how and why shockwaves produce effects on stone and tissue. Current knowledge suggests that stones fragment by the mechanisms of compression fracture, spallation, squeezing, and acoustic cavitation, while tissue damage from shockwaves is secondary to cavitation and non-cavitational forces such as sheer stress. It appears likely that most tissue damage from shockwaves is caused by cavitation. As the understanding of SWL matures, new lithotripter designs may emerge that truly represent an improvement on the original Dornier HM3 machine.

MR imaging of kidneys: functional evaluation using F-15 perfusion imaging

BACKGROUND

Children with hydronephrosis are typically investigated by a combination of diuretic renal scintigraphy, ultrasound, and voiding cystourethrography. Unfortunately, there is no gold standard to assess obstruction.

PURPOSE

The purpose of our study was to evaluate the utility of dynamic contrast enhanced MR urography in the investigation of children with hydronephrosis to define urinary tract anatomy, to calculate differential renal function and to assess urinary tract obstruction.

MATERIALS AND METHODS

Dynamic contrast-enhanced MR imaging was performed in 40 children with unilateral hydronephrosis. There were 14 girls and 26 boys with an age range of 1 month to 14 years (mean 1.4 years). The information from traditional imaging modalities was compared to the information obtained from the single MR study.

RESULTS

The anatomic imaging with MR urography was superior to other modalities. The split renal function was estimated with MR urography by calculating the volume of enhancing renal parenchyma and was comparable to renal scintigraphy ( r=0.98). By using surgery versus non-surgery as the decision point, with MR urography the sensitivity was 100%, specificity 71%, positive predictive value 86%, negative predictive value 100%, and diagnostic efficiency 90%. For renal scintigraphy the sensitivity was 96%, the specificity 56%, positive predictive value 76%, negative predictive value 90%, and diagnostic efficiency 79%.

CONCLUSIONS

Dynamic contrast-enhanced MR urography provides superior anatomic and functional information when compared with ultrasound and diuretic renal scintigraphy. The information is gathered in a single study that does not use ionizing radiation. It is likely that MR urography will replace renal scintigraphy in the evaluation of hydronephrosis in children.