Diagnostic Difficulty in Interpretation of Tc-99m MAG3 Dynamic Renal Scan: Intrarenal Reflux or Delayed Concentration Function?

An 11-year-old boy with a neurogenic bladder had a Tc-99m MAG3 dynamic renal scan to evaluate the split renal function. The left kidney could not be visualized on perfusion imaging and early static studies but started to concentrate radionuclide at the 6th minute. At first glance, the scintigraphic appearance implied delayed concentration and stasis in the excretion phase. However, further evaluation of the images and the renogram curve suggested intrarenal reflux (IRR) resulting from reciprocal changes in the bladder and kidney curves. Because it is not a usual finding to see IRR in the early concentration phase when the bladder is relatively empty, there was further evaluation with renal parenchymal scintigraphy. The left kidney was nonfunctioning on a Tc-99m DMSA scan, suggesting IRR as the most probable diagnosis. Voiding cystourethrography also confirmed left IRR and hydronephrosis was demonstrated later. This case illustrates the potential misinterpretation of a Tc-99m MAG3 dynamic renal scan in the presence of nonfunctioning renal tissue and IRR. However, a careful review of the renogram pattern established the correct diagnosis, obviating the need for further investigation.