Misinterpretation of radioisotope imaging in pelvic kidneys.

We report the case of a gentleman referred with apparent worsening function in a hydronephrotic left-sided pelvic kidney. Imaging with Tc-99m-Mercaptoacetyltriglycine (MAG 3) in 1999, showed that the left kidney contributed 46% of renal function with no evidence of obstruction. Three years later, repeat scanning showed ectopic kidney function had decreased to 20% and with worsening pain, nephrectomy had been suggested. Review of the second MAG 3 scan revealed that only posterior images had been obtained. With pelvic kidneys, the pelvis forms a barrier between the radioactively labelled tracer and the gamma camera, thus, reducing the amount of radiation detected and underestimating function. A subsequent Dimercaptosuccinic acid scan (DMSA) was carried out with posterior and anterior images, the latter showing split renal function was identical to that seen on the initial scan. In patients with pelvic kidneys, anterior views must be obtained during radionuclide scanning if unnecessary nephrectomy is to be avoided.