Case Presentation: A 20-year-old male with a family history of Hepatoblastoma in his brother, presented with a two-week history of intermittent left lower quadrant abdominal pain. He was afebrile and initial work-up showed a normal White blood cell count (WBC), Hemoglobin (Hg) 7.1 g/dl, Mean corpuscular volume (MCV) 71 femtoliters and a positive stool occult test. A CT scan of the abdomen showed diffuse thickening of the left colon wall, streaky nodular stranding of the omental fat and mild ascites. A CT scan of the chest showed multiple pulmonary nodules. Colonoscopy revealed hundreds of non-bleeding polyps concerning for familial adenomatous polyposis (FAP) with biopsy results showing adenomatous polyps. Subsequent biopsy of a lung nodule showed metastatic adenocarcinoma of colonic origin. Two days after the colonoscopy, he developed worsening abdominal pain, and a distended rigid abdomen on an exam. Repeat CT scan revealed new large volume loculated ascites as well as peritoneal thickening consistent with peritonitis. There was no evidence of intestinal perforation on CT scan. Ascitic fluid analysis from paracentesis revealed 11,000 WBCs and cultures grew group C streptococci. He was started on broad-spectrum parenteral antibiotics with evidence of complete resolution of the collection on repeat CT scan. However, one week later, the patient returned with a fever and recurrent abscess on CT scan, which was not amenable to percutaneous drainage. He underwent surgical drainage of the abscess. He recovered from surgery well and was started on chemotherapy pending genetic testing for FAP.

Discussion: Colonoscopy is a relatively low risk procedure used for screening, diagnosis and treatment of diseases of the colon. Peritonitis is an infection of the peritoneum and is deemed spontaneous or primary if it occurs without any intra-abdominal source of infection. Primary peritonitis is a rare complication of colonoscopy and related procedures such as polypectomy. To our knowledge this is the first reported case of primary peritonitis following colonoscopy in a patient with malignant ascites. Malignancy is an overall immunocompromised state, which poses a risk for infections including peritonitis. Although causality cannot be established in our case, we display a temporal sequence of association between the colonoscopy and the onset of peritonitis.

Conclusions: Theoretically colonoscopy and related procedures increase the transmural migration of normal flora from the bowel into the peritoneal cavity, which can lead to peritonitis. However, due to lack of sufficient evidence prophylactic antibiotics are not recommended in patients undergoing colonoscopy. Physicians should be cognizant of this potential complication following colonoscopy, especially in patients who are vulnerable to infections such as those with malignancy.