Dual isotope imaging with Ga-67 and Tc-99m mercaptoacetyltriglycine (MAG3) can assist in identifying pyonephrosis. A 70-year-old man with retroperitoneal fibrosis developed fever of unknown origin following bilateral ureteral stent placement.
Ga-67 scan reveals focal, intense activity in the left flank. Tc-99m MAG3 renogram shows a focus of photon deficiency in the superior pole of the left kidney. This photopenic lesion corresponds with the intense Ga-67 activity.
The pyonephrosis was diagnosed and confirmed with fine-needle aspiration. This diagnosis was not clear from the CT scan, which demonstrated persistent hydronephrosis of the left kidney. Subsequently, the patient was found to have a duplicated left collecting system. The upper pelvis had not been stented and became infected secondary to lack of drainage.