Case Study - May 2012

What are the abnormalities shown?

What should be done next?

What are the possible causes?

How does a MAG3 renogram work?

Reveal Answer

Right sided bifid ureter which joins in the middle third to form a single ureter and single ureteric orifice (confirmed on cystoscopy).

The left pelvicalyceal system appears to be dilated with a sharp transition point at the pelvico-ureteric junction, consistent with possible left pelvicoureteric junction obstruction.

If the patient is symptomatic from the left sided abnormality pain (particularly on drinking large quantities of fluid, known as Reidels crisis), recurrent infections or stones then the patient should have a MAG3 renogram to assess drainage. If they wanted treatment, they could be offered a open or laparoscopic pyeloplasty.

Congenital – intrinsic obstruction, crossing vessels, high ureteric insertion, vesicoureteric reflux and scarring, polyps and congenital valves. Acquired – stones, tumour, extrinsic cause (retroperitoneal
fibrosis), inflammation, chronic infection.

The patient is given IV technetium-99m mercaptoacetyltriglycine (MAG3). MAG3 is taken up by the
kidneys by tubular secretion (98%) and glomerular filtration (2%). 90% of it is protein bound and 40% of the MAG3 in the blood is taken up into the kidneys everytime blood circulates through the kidneys. 70% of the MAG3 is in the urine 30mins after injection. Serial images are taken with a gamma camera to assess
uptake of the radioactive compound by the kidneys and then subsequent drainage. Region of interests are drawn by hand to allow the software to calculate where the kidneys are. Four stages of the renogram can be measured –perfusion, uptake, excretion and clearance and demonstrated graphically.

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