Case Seven - Acute Pyelonephritis
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Findings: A 99m Technetium-mercapto acetyl glycine (99mTc-MAG3) renogram demonstrates diminished but not delayed uptake of radiopharmaceutical by the left kidney. The delayed, static images show a faintly outlined left kidney with regions of relatively decreased activity. On CT, an edematous left kidney is seen with multiple large areas of decreased enhancement in the periphery. Ultrasound images reveal an enlarged left kidney with heterogeneous echo texture as well as several discrete areas of hyopechogenicity which correspond to the regions of low attenuation seen on CT.
Diagnosis: Acute Pyelonephritis.
Discussion: UTI’s occur in up to 3% of girls and 1% of boys. Early diagnosis and treatment are important in preventing renal scarring which increases the risk for subsequent hypertension and renal failure. Radionuclide renal imaging with either 99mTc-dimercaptosuccinic acid (99mTc-DMSA) or 99mTc-MAG3 can demonstrate defects in renal function secondary to either acute parenchymal inflammation or renal scarring. 99mTc-MAG3, which was used in this case, is excreted both by glomerular filtration and active tubular secretion. This makes it useful in approximating effective renal plasma flow. Radionuclide renal imaging findings seen in acute pyelonephritis include decreased or absent uptake of tracer in the renal cortex causing distortion or indentation of the normal renal outline and/or significant reduction in the function of one kidney. Both of these findings were present on the 99mTc-MAG3 study presented with regions of decreased radionuclide activity in the left kidney as well as differential or relative renal function of 13% on the left and 87% on the right.
Findings consistent with acute pyelonephritis were also seen on CT and ultrasound. In addition, regions of parenchymal necrosis were identified.
References:
Clarke et al. Technetium-99m-DMSA Studies in Pediatric Urinary Tract Infection.
The Journal of Nuclear Medicine 1996;37:823-828.
Murray et al. Nuclear Medicine in Clinical Diagnosis and Treatment. 1994;201-204, 249-256.
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