Case Presentation: A 71-year-old woman with a history of bilateral staghorn calculi and morbid obesity presented with progressively worsening left flank pain. Three weeks prior, the patient underwent right-sided ureteroscopy with basket stone extraction and left-sided laser lithotripsy with attempted percutaneous nephrolithotomy following bilateral ureteral stent placement. Prophylactic intravenous (IV) meropenem was given perioperatively due to a history of persistent multidrug resistant bacteriuria. On admission, the patient was afebrile and tachycardic (105 bpm) with physical exam notable for severe left flank tenderness. Labs revealed leukocytosis (WBC 20,000 cells/µL; trending down from 29,000 cells/µL three weeks prior), procalcitonin 0.35 ng/mL, CRP 276 mg/L, and creatinine 1.67 mg/dL (baseline 1.4). Urinalysis showed >50 WBC/HPF and positive nitrites. A non-contrast abdominal CT showed a 7.4 x 6.8 cm left retroperitoneal lobulated collection consistent with hematoma. A follow up contrast CT 48 hours later showed expansion to 9.0 x 7.2 cm without obvious rim enhancement. A course of empiric IV cefepime was initiated for complicated urinary tract infection but her left flank pain continued to worsen. Pain on serial exams was deemed out of proportion to a simple hematoma raising suspicion for abscess. Interventional radiology placed a drain on day 8, revealing copious purulent drainage. Her pain improved rapidly following the procedure, and a follow up CT one week later showed resolution. The patient was discharged to a subacute rehabilitation facility to complete a three-week course of IV meropenem for polymicrobial abscess growing ESBL E. coli, Klebsiella pneumoniae, and Streptococcus anginosus.
Discussion: Retroperitoneal abscess following ureteroscopy is a diagnostic challenge. The reported incidence of retroperitoneal abscess or hematoma after ureteroscopy is low (up to 2.2%), compared to the 15% incidence of fevers or urinary tract infection. High intra-renal pressure during ureteroscopy and iatrogenic trauma during manipulations are proposed mechanisms. Risk factors for infection include large stones, staghorn calculi, severe hydronephrosis, and longer operative duration. Higher irrigation pressure is also an important risk factor after lithotripsy. Most reported perinephric abscesses after ureteroscopy present with both fevers and pain. Abscesses resulting from extracorporeal shock wave lithotripsy (ESWL) or spontaneous infection often present with only severe pain or tenderness. Our patient presented with left flank pain without fever, suggesting the infection spread mainly within the retroperitoneal space, like the abscess caused by ESWL. The abscess was initially misdiagnosed as a hematoma due to its homogeneous density mimicking blood and its lack of clear rim enhancement on contrast CT. However, rapid interval expansion three weeks post procedure and tenderness out of proportion to the imaging findings were key diagnostic cues pointing toward an inflammatory/infectious process.
Conclusions: Hospitalists should keep a high index of suspicion for retroperitoneal abscess in patients with presumed hematoma following ureteroscopy/lithotripsy, even in the absence of fever or traditional markers of infection. Evolving retroperitoneal fluid collections at atypical time intervals and pain out of proportion to the size of the collection are critical diagnostic clues.