Abdomen / Pelvis for Tuesday, June 2nd, 2026

Contributed by Mayo Clinic Rochester
Minsoo Kim, and Kelly Horst.

History

3-year-old male with epilepsy and recent inpatient admission for breakthrough seizures in the setting of RSV infection, now presenting to the ED with lethargy.

Images (Click any image to enlarge)

CT of the abdomen and pelvis shows a diffusely enlarged left kidney with striated nephrogram, wedge-shaped areas of cortical hypoenhancement, and multiple hypoattenuating renal parenchymal lesions.
Renal ultrasound shows multiple small complex cystic structures within the left kidney without internal color Doppler flow.
MRI of the abdomen shows multiple renal parenchymal lesions corresponding to the findings on CT and ultrasound which demonstrate T1 hypointensity, mild T2 hyperintensity, diffusion restriction, and peripheral enhancement. T2-weighted image with fat saturation shown.
DWI.
ADC map.
Post-gadolinium MRI.

Question

What is the next best step in management?

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Correct answer

Empiric IV antibiotics

Discussion

Urinary tract infections (UTIs) are common in the pediatric population. Risk factors for UTI in this population include younger age, congenital anomalies of the urinary tract, bowel and bladder dysfunction, neurogenic bladder, sexual activity, and genetic susceptibility [1, 2]. In particular, vesicoureteral reflux is a risk factor for pyelonephritis, thought due to retrograde transport of bacteria to the kidneys from the bladder [1]. Renal abscess can arise as a rare complication of pyelonephritis or via hematogenous spread [3], and may present with nonspecific symptoms including fever, lacking other typical lower UTI symptoms [4]. E. coli is the most common causative organism [2, 5]. Ultrasound is recommended to evaluate the urinary tract anatomy without the use of ionizing radiation, typically after resolution of infection in order to minimize acute inflammatory changes [1]. Early ultrasound in UTI may be indicated when there is concern for renal or perinephric abscesses or high-grade obstruction [1]. However, ultrasound has been shown to lack sensitivity in detecting renal abscess, particularly for small lesions [4, 5]. The typical imaging appearance for a renal abscess is a well-circumscribed renal cortical lesion that is hypoechoic on ultrasound, hypoattenuating on CT, T1 hypointense and T2 hyperintense on MRI with diffusion restriction, and peripherally enhancing on contrast-enhanced imaging [3-5]. Most cases respond to antibiotic treatment, although intervention such as percutaneous drainage may be considered for large abscesses [3-5]. In our patient, ultrasound-guided aspiration was pursued due to concern for clinical deterioration. The patient eventually improved with IV ceftriaxone and was able to be discharged with outpatient follow-up.

Additional images

Follow-up outpatient US shows a hypoechoic area in the interpolar region, likely healing abscess/scarring.

References

  • Marsh MC, Junquera GY, Stonebrook E, Spencer JD, Watson JR. Urinary Tract Infections in Children. Pediatr Rev. 2024 May 1;45(5):260-270. doi: 10.1542/pir.2023-006017. PMID: 38689106.
  • John PP, Mike L, Mysorekar IU, Ruiz-Rosado JD, Clatworthy M, Schwartz L, Ching C, Kimbrough D, Shaikh N, Braga L, Rajadhyaksha E, Hains D, Watson J, Becknell B. Urinary tract infections in children. Nat Rev Urol. 2026 Feb 26. doi: 10.1038/s41585-026-01130-1. Epub ahead of print. PMID: 41748741.
  • El Abiad Y, Roukhssi R. Imaging-guided drainage of renal abscess: A case report and literature review. Urol Case Rep. 2021 Sep 13;39:101852. doi: 10.1016/j.eucr.2021.101852. PMID: 34603967; PMCID: PMC8463828.
  • Sun J, Shi L, Ye L, Xu Y. Pediatric renal abscess: clinical analysis and literature review. Front Pediatr. 2025 Apr 28;13:1407437. doi: 10.3389/fped.2025.1407437. PMID: 40356779; PMCID: PMC12066547.
  • Guo JQ, Gao MH, Ma YJ, Jia SL, Gao XJ, Li J. Pediatric renal abscess: a 12-year single-center retrospective analysis. Pediatr Nephrol. 2026 Mar 27. doi: 10.1007/s00467-025-07114-4. Epub ahead of print. PMID: 41888477.