Acute Bacterial Nephritis in an 8-Year-Old Boy Presenting with Abdominal Pain: A Diagnostic Challenge

Case Report

Acute Bacterial Nephritis in an 8-Year-Old Boy Presenting with Abdominal Pain: A Diagnostic Challenge

Cindy Gomes ID ^1*
Claúdia Rodrigues ¹
Ana Isabel Duarte ID ²

1Department of Pediatrics, Unidade Local de Saúde Médio Tejo, Torres Novas, Portugal.

2Department of Pediatrics, Unidade Local de Lezíria, Santarém, Portugal.

*Corresponding Author: Cindy Gomes, Department of Pediatrics, Unidade Local de Saúde Médio Tejo, Torres Novas, Portugal.

Citation: Gomes C, Rodrigues C, Duarte AI. (2026). Acute Bacterial Nephritis in an 8-Year-Old Boy Presenting with Abdominal Pain: A Diagnostic Challenge, International Clinical and Medical Case Reports, BioRes Scientia Publishers. 5(3):1-3. DOI: 10.59657/2837-5998.brs.26.064

Copyright: © 2026 Cindy Gomes, this is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Received: May 26, 2026 | Accepted: June 17, 2026 | Published: July 13, 2026

Abstract

Acute bacterial nephritis, also known as acute lobar nephronia or focal bacterial nephritis, is an uncommon localized infection of the renal parenchyma without liquefaction. It may mimic other causes of acute abdominal pain in children, particularly when urinary symptoms are absent. We report the case of an 8-year-old previously healthy boy presenting with high fever and right-sided abdominal/flank pain, initially interpreted as mesenteric adenitis. Persistent fever, worsening inflammatory markers, and absence of an obvious infectious focus prompted contrast-enhanced abdominal computed tomography, which revealed hypoperfused areas in the upper pole of the right kidney, consistent with acute bacterial nephritis. He improved with intravenous cefuroxime followed by oral cefuroxime-axetil, completing four weeks of therapy. Follow-up ultrasound and 99mTc-DMSA scintigraphy confirmed complete resolution without renal scarring. This case highlights the need to consider acute bacterial nephritis in children with persistent fever and abdominal pain, even without urinary complaints.

Keywords: acute lobar nephronia; acute bacterial nephritis; focal bacterial nephritis; urinary tract infection; abdominal pain; child

Introduction

Acute bacterial nephritis (ABN), also referred to as acute lobar nephronia or focal bacterial nephritis, is a localized, non-liquefactive bacterial infection of the renal parenchyma. It represents an intermediate entity in the spectrum of upper urinary tract infections, between uncomplicated acute pyelonephritis and renal abscess [1].

The condition was first described radiologically in adults by Rosenfield et al. in 1979 and was subsequently reported in children by Lawson et al. in 1985 [2,3]. In pediatrics, ABN remains diagnostically challenging because it may present with nonspecific fever, abdominal or flank pain, and elevated inflammatory markers, while urinary symptoms, pyuria, and positive cultures may be absent [1,4].

Early recognition is important because ABN usually requires longer antimicrobial therapy than uncomplicated pyelonephritis and may progress to renal abscess or renal scarring when treatment is delayed or insufficient [5-7]. We report a case of ABN in a previously healthy child presenting predominantly with fever and abdominal pain, initially suggestive of mesenteric adenitis.

Case Presentation

An 8-year-old previously healthy boy presented to the emergency department on the first day of illness with high fever, with a maximum axillary temperature of 40 degrees Celsius, and abdominal pain localized to the right flank and right iliac fossa. The pain worsened with deep inspiration, coughing, and movement. He also had anorexia and a slight cough, without respiratory distress. There was no vomiting, diarrhea, dysuria, urinary frequency, hematuria, or other gastrointestinal or urinary complaints.

Physical examination revealed tenderness on palpation of the right flank and right iliac fossa, without signs of peritoneal irritation. Initial laboratory tests showed leukocytosis of 30,580/µL with neutrophilia of 27,800/µL and elevated C-reactive protein (CRP) of 12.48 mg/dL. Renal function, electrolytes, and liver enzymes were normal. Because acute appendicitis was initially suspected, the child was evaluated by Surgery and underwent abdominal ultrasound, which suggested mesenteric adenitis. He was discharged with symptomatic treatment.

On the third day of illness, he returned to the emergency department because of persistent right-sided abdominal pain and worsening fever, with high temperatures that were difficult to control with antipyretics. He had no new respiratory, gastrointestinal, or urinary complaints. Physical examination again showed right flank and right iliac fossa tenderness, with no peritoneal signs. Repeat laboratory evaluation showed improvement in leukocytosis to 16,830/µL and neutrophilia to 14,640/µL, but worsening inflammatory response, with CRP of 27.76 mg/dL. Renal function, electrolytes, and liver function remained normal.

Given the absence of a clear infectious focus, additional investigations were performed. Chest radiography showed no pulmonary consolidation. Respiratory viral testing was positive for SARS-CoV-2; however, SARS-CoV-2 serology showed positive IgG and negative IgM, suggesting previous rather than acute infection. A midstream urine sample showed proteinuria of 50 mg/dL and ketonuria of 150 mg/dL, without relevant urinary symptoms. Blood and urine cultures were negative.

Because of persistent fever, localized abdominal/flank pain, and worsening inflammatory markers, contrast-enhanced abdominal computed tomography (CT) was performed. CT identified hypoperfused areas in the upper pole of the right kidney, without cavitation, consistent with acute bacterial nephritis.

The child was admitted and started intravenous cefuroxime. Abdominal pain progressively improved, although fever persisted until the seventh day of hospitalization. On the fourth day of hospitalization, because fever persisted despite clinical improvement, laboratory tests and imaging reassessment were repeated. Inflammatory parameters had clearly improved, and imaging findings were stable, with no evidence of abscess formation.

During hospitalization, abdominal pain resolved by the fifth day, appetite gradually improved, and oral tolerance remained good. After seven days of intravenous antibiotic therapy and sustained apyrexia, follow-up renal ultrasound showed parenchymal heterogeneity with hypo- and hyperechoic areas in the upper pole of the right kidney. After multidisciplinary discussion, oral cefuroxime-axetil was prescribed to complete a total of four weeks of antimicrobial therapy.

At follow-up, the child remained asymptomatic. A control ultrasound performed at the end of antibiotic therapy showed complete resolution of the previous parenchymal changes, particularly in the right kidney. Subsequent renal scintigraphy with 99mTc-dimercaptosuccinic acid (DMSA) showed both kidneys with normal morphological and functional appearance, without focal defects or evidence of renal scarring.

Discussion

ABN is uncommon but clinically relevant because it may be underdiagnosed in children with persistent fever and abdominal pain. The clinical presentation is often insidious and can mimic appendicitis, gastroenteritis, pneumonia, or mesenteric adenitis [1,4,5]. In the present case, the initial localization of pain to the right iliac fossa and the first ultrasound findings led to the presumptive diagnosis of mesenteric adenitis.

The absence of urinary symptoms does not exclude ABN. Recent pediatric series have emphasized that pyuria and positive urine cultures may be absent, particularly when renal involvement is focal or when urine sampling occurs early in the disease course [1]. This feature was clinically relevant in our patient, who had no dysuria, frequency, or hematuria, and whose urine and blood cultures remained negative.

Laboratory findings are also nonspecific. Leukocytosis, neutrophilia, and markedly elevated CRP are commonly described, but these abnormalities do not identify the source of infection [1,5]. Therefore, persistent fever, localized flank or abdominal pain, and increasing inflammatory markers despite an initially reassuring or nonspecific evaluation should prompt reconsideration of the differential diagnosis.

Imaging is central to diagnosis. Ultrasound is often the first imaging modality used in children because it is widely available and avoids ionizing radiation; however, it may be normal or nonspecific in early ABN [4,5]. Contrast-enhanced CT is considered the most sensitive diagnostic test, typically showing poorly defined, wedge-shaped or lobar hypoperfused areas without liquefaction or abscess formation [1,4]. In this case, CT was decisive after the initial ultrasound suggested a non-renal diagnosis.

Antibiotic therapy for ABN is generally longer than for uncomplicated acute pyelonephritis. Cheng et al. showed that a three-week intravenous-plus-oral antimicrobial regimen was more effective than a two-week regimen in pediatric acute lobar nephronia [6]. Persistent fever during the first days of adequate therapy may occur and does not necessarily indicate therapeutic failure if clinical condition and inflammatory markers improve [5,6]. In our patient, fever resolved only on the seventh day of hospitalization, while pain and laboratory markers improved progressively.

Post-treatment imaging follow-up is justified because ABN has been associated with renal scarring and, less commonly, progression to abscess [6,7]. In this case, the favorable clinical course, normalization of ultrasound findings, and normal DMSA scintigraphy confirmed resolution without detectable permanent renal damage.

This report reinforces the diagnostic value of maintaining a high index of suspicion for ABN in children with persistent fever, localized abdominal or flank pain, and elevated inflammatory markers, even when urinary symptoms and urine cultures are absent.

Conclusion

Acute bacterial nephritis should be included in the differential diagnosis of children presenting with persistent fever, right-sided abdominal or flank pain, and elevated inflammatory markers, even in the absence of urinary complaints, pyuria, or positive urine culture. A nonspecific initial ultrasound does not exclude the diagnosis. Timely CT imaging, appropriate prolonged antibiotic therapy, and post-treatment imaging follow-up are essential to confirm resolution and reduce the risk of renal abscess or long-term renal scarring.

Declarations

Author Contributions

Cindy Gomes contributed to the conception of the manuscript, acquisition and interpretation of clinical data, literature review, drafting, critical revision, and final approval of the manuscript.

Claúdia Rodrigues contributed to the conception of the manuscript, drafting and critical revision.

Ana Isabel Duarte contributed to the conception of the manuscript, drafting and critical revision.

Competing Interests

The author declares no competing interests.

Grant Information

The author received no specific funding for this work.

Acknowledgments

None.

References

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