Purpose/Background: Pneumoperitoneum on imaging typically signifies hollow-viscus perforation requiring urgent exploration. [1] A minority of patients demonstrate benign or non-surgical pneumoperitoneum due to mechanical ventilation, postoperative residual air, or infection by gas-forming organisms.[2-3] The Proteus mirabilis species are anaerobic Gram-negative bacilli (GNB) capable of urease production and gas formation under high-glucose or low-oxygen conditions.[4] We present an unusual case of Proteus-associated peritonitis in a patient with neurogenic bladder and cystitis, imitating pneumoperitoneum without intra-abdominal perforation.
Results/Outcomes: We report a case of a 74-year-old male with a medical history of alcohol use disorder and a neurogenic bladder presenting with diffuse abdominal pain. Examination showed abdominal distension, peritonitis and guarding. CT scan revealed a right upper quadrant fluid collection extending along the mid-right abdomen. Within this collection was extraluminal air raising concern for abscess formation and pneumoperitoneum. Also noted was a distended bladder with wall thickening consistent with cystitis.
Given the imaging and clinical peritonitis, the patient underwent urgent exploratory laparotomy via a midline incision. On entry there was murky fluid encountered most prominent in the right paracolic gutter. The gallbladder was noted to be distended, and the small and large bowel were examined without evidence of perforation or ischemia. Subcapsular oozing from the inferior pole of the spleen was noted, likely traction related in the setting of mild coagulopathy. The abdomen was packed and left open. On re-exploration, no hollow-viscus perforation was noted. Oozing from the spleen was again noted and a splenectomy was performed, followed by abdominal closure. Peritoneal cultures obtained intra-operatively grew Proteus mirabilis, urine culture yielded 10,000 CFU/mL oxidase-negative non-lactose-fermenting GNB. Blood cultures were sterile. Empiric ceftriaxone and metronidazole was initiated. Following culture reports, therapy was narrowed to oral ciprofloxacin for six weeks to cover chronic prostatitis and urinary source peritonitis. The patient improved and was discharged in stable condition.
Conclusion/Discussion: Proteus mirabilis is a cunning pathogen. It is known for urinary tract infections and its ability to produce urease allows it to form gas.[4] In our patient, the coexistent cystitis and peritoneal fluid Proteus growth suggests seeding of bacteria from the urinary tract into the peritoneal fluid with production of intraperitoneal gas. Emphysematous infections of the bladder, kidneys, and gallbladder have been seen, but translocation into the peritoneal cavity without peritoneal dialysis or paracentesis is rare. [4-6]
For surgeons, pneumoperitoneum is an anxiety-provoking imaging finding. This case highlights the importance of intraoperative judgment. When exploration reveals no perforation, resection is not warranted. The wiser approach is thorough exploration, irrigation, source control, and sending cultures. In this case, a few milliliters of murky fluid told the story that the CT could not.
Pneumoperitoneum does not always equate to gastrointestinal perforation. [1] Gas-forming organisms, such as Proteus mirabilis, can blur the line. [4] As surgeon’s, having awareness of these mimics can help reinforce the value of intra-operative judgement over imaging alone.
