MRI superior to static renal scintigraphy in detecting lesions in children with acute pyelonephritis
The diffusion-weighted magnetic resonance imaging (DW-MRI) facilitates rapid imaging of acute inflammatory or multifocal lesions in the renal parenchyma in children with acute pyelonephritis, demonstrating a higher sensitivity compared with 99mTc-dimercaptosuccinic acid static renal scintigraphy (DMSA-SRS), a study has found.
“[DW-MRI] could help establish the diagnosis of acute pyelonephritis in clinically unclear cases and provides more precise information about the extent of acute parenchymal involvement,” the investigators said.
The study included 31 children (median age 11 years) with a first episode of febrile urinary tract infection [UTI], none of whom had a previously detected congenital malformation of the urinary tract. DMSA-SRS and DW-MRI were performed within 5 days of acute pyelonephritis diagnosis to detect renal inflammatory lesions, and after 6 months to detect late lesions.
DW-MRI showed acute inflammatory changes in the renal parenchyma in all 31 patients, whereas DMSA-SRS detected inflammatory lesions in only 22 (100 percent vs 71 percent; p=0.002). Multiple lesions were seen with greater frequency on DW-MRI (84 percent vs 40 percent). [J Pediatr Urol 2018;doi:10.1016/j.jpurol.2018.02.014]
At the follow-up examination, none of the patients had a recurrent UTI or acute pyelonephritis during the interval between investigations. The incidence of scars was low, with both DW-MRI and DMSA-SRS detecting scarring of the renal parenchyma in five patients (16 percent), three of whom were the same patients.
The overall concordance of late findings (normal and scars) for both methods was found in 87.1 percent of patients, and the scars corresponded with the anatomical location of acute and late lesions.
“These results led us to conclude that DW-MRI is more sensitive for diagnosing acute pyelonephritis and shows a larger extent of the lesions than does DMSA-SRS,” the investigators said.
Furthermore, the fact that the procedure is done without contrast agent, lasts 8–10 minutes and can be performed without general anaesthesia in children aged older than 3 years contribute significant advantages to the DW-MRI examination. The only downside is this modality is about 2.5 times more expensive than DMSA-SRS.
As the investigators pointed out, DW-MRI could replace DMSA-SRS, which is associated with radiation burden, poor visualization of calyceal anatomy and limited specificity. Additional studies must be conducted to test its ability to discriminate which acute lesions will become clinically significant and develop into a scar, as well as confirm its utility in children under 3 years of age with the aim of replacing DMSA scintigraphy in detecting renal scars.