A 10-year-old girl without significant past medical history presented with 1 week of fever and intermittent vomiting with 1 day of abdominal pain and localized discomfort over the left hypochondrium. Two weeks prior to this presentation, she had 4 days of fever with diarrhea and vomiting which resolved spontaneously. There was no recent history of trauma, sick contact, or travel history, except for a superficial scratch (<2 cm open wound) caused by a household cat 3 months prior, which healed without intervention.
On physical examination during admission, she was alert and non-toxic, had costovertebral angle tenderness on the left side, but did not report any dysuria or increase in urinary frequency. She was febrile at 38.5 C, with other vitals being stable. Laboratory evaluation revealed leukocytosis and elevated inflammatory markers (Table 1). Urinalysis done was unremarkable and no microorganism was isolated from her urine culture. She had microcytic hypochromic anemia and was subsequently diagnosed to have alpha 2:thalassemia minor during this admission.
Due to the concerns of pyelonephritis or colitis, an ultrasound of the abdomen was ordered on the second day of admission. Imaging of both kidneys showed multiple cysts and a heterogeneous structure 4.2 cm x 4.0 cm x 3.1 cm (Figure 1A) extending from the left mid to the lower pole, consistent with a renal abscess, and much of it appeared liquefied. Her parents declined genetic testing for polycystic kidney disease and there was no known family history of kidney cysts.
Intravenous (IV) gentamicin (5 mg/kg/day) was initiated on admission for concerns of pyelonephritis but was switched to IV ceftriaxone (100 mg/kg/day) after a renal abscess was detected, for better abscess penetration. Subsequently, an image-guided drainage of the renal abscess was done, where 15 mL of brown frank pus was aspirated and the drain was left in situ. The fluid culture revealed a group C Salmonella species (serotyped as Salmonella serovar Oranienburg by Singapore National Public Health Laboratory) that was susceptible to ampicillin, ceftriaxone, and co-trimoxazole. All other microbiological investigations including blood culture, repeat urine culture, acid-fast bacilli smear of the pus, Mycobacterium tuberculosis polymerase chain reaction, mycobacterial culture and fungal culture were unremarkable. A stool culture was not performed as her diarrhea resolved prior to admission. As group C Salmonella is an atypical cause of renal abscess, an immunological screen consisting of immunoglobulin levels and CD3, CD4, and CD8 T cells count was performed, which was unremarkable.
Serial kidney ultrasounds were done on day 3, day 10, and day 27 post-drainage. Her fever lysed by the second day post-drainage, and by day 3 post-drainage, the renal abscess decreased to 2.0 cm x 1.9 cm x 1.9 cm (Figure 1B). Her C-reactive protein normalized by day 10 post-drainage (4.1 mg/L), with a further decrease in renal abscess size to 2.1 cm x 1.4 cm x 1.6 cm (Figure 1C). Hence, the drain was removed. After receiving 2 weeks of intravenous ceftriaxone, she was discharged with another 4 weeks of oral co-trimoxazole (4 mg/kg/dose twice daily of trimethoprim component). By day 27 post-drainage, the abscess had resolved completely on the ultrasound scan (Figure 1D).