Presentation
Recurrent urinary tract infections, with most recent infection 4 months ago.
Patient Data
There is heterogeneous uptake of tracer in both kidneys, more marked on the left. In the left kidney, the outline is irregular with multiple wedge shaped areas of photopaenia in keeping with multiple renal cortical scars. In the right kidney, there is a focal defect in the interpolar region as well as irregularity at the inferior pole also in keeping with further scarring.
Renal function is asymmetric, with the left kidney contributing 35.7% to overall function and the right contributing 64.3%.
Case Discussion
99mTc-DMSA is a useful tracer for evaluating the renal parenchyma, and is particularly useful for the evaluation of renal cortical scarring, as in this case. Children with recurrent urinary tract infections, especially in the setting of vesico-ureteric reflux, are at risk of renal cortical scarring and reflux nephropathy. In some cases, extensive scarring can impact overall renal function - as in this case where the function of the left kidney has been reduced.
Patients ideally should not be imaged within 2-3 months of the most recent urinary tract infection as pyelonephritis can mimic the appearance of renal cortical scarring on DMSA scan.
Differential renal function can be calculated by geometric mean on planar imaging, which takes into account the relative depths of the kidneys to correct the amount of counts which are reaching the gamma camera.
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