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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.
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.
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
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