EXCRETORY MAGNETIC RESONANCE (MR) UROGRAPHY

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Figure 1

History: Ultrasound and CT exams on a 60 year old female with left flank pain revealed moderate left hydronephrosis without calculus. A left-side retrograde pyelogram was performed by a urologist (Figure 1), which revealed moderate hydronephrosis and normal caliber left ureter, compatible with ureteropelvic junction (UPJ) obstruction. The patient was then referred to Main Street Radiology for magnetic resonance angiogram (MRA) of the renal arteries as well as an MR urogram.


Technique: Gadolinium-enhanced MRA of the renal arteries is first performed utilizing a 3D breath-hold sequence during the dynamic injection of contrast utilizing a power injector. 10 mg of furosemide is injected with the MR contrast to facilitate excretion and to achieve uniform distribution of contrast in the urinary tract. MR urography images are also obtained utilizing a 3D breath-hold sequence, approximately 2 minutes following the administration of contrast.


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Figure 2

Findings: On the MR urographic image (Figure 2), findings of left UPJ obstruction are visualized. Incidental note of a small and scarred right kidney is made. An oblique image from the MRA (Figure 3) demonstrates early branching of the main renal artery with the inferior branch (arrow) crossing the expected location of the obstruction.


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Figure 3

Discussion: There are numerous causes of UPJ obstruction, including calculus, tumor, crossing vessel, and congenital/inflammatory stricture. When calculus and tumor are excluded with CT and retrograde pyelogram, and corrective surgical procedure is planned, the presence of a crossing vessel should be determined prior to intervention. Traditionally, conventional catheter arteriography was performed; however, with the advent of gadolinium-enhanced MRA, vascular anatomy can be imaged without performing an invasive procedure. An excretory MR urogram can be obtained on the same scan, which is analogous to a conventional IVP, providing anatomical correlation with the urinary tract.

In studying the urinary tract, MR urography has been utilized as an alternative to conventional IVP for patients who cannot receive iodinated contrast due to allergy or renal insufficiency. Non-nephrotoxic gadolinium is used for MR urography. The accuracy in detecting the site of obstruction has been reported to be greater than 99%.

To the best of our knowledge, MSR is the only facility in Queens performing MR urography. Superior equipment and highly-trained personnel enable MSR to perform procedures traditionally reserved for major academic centers.