Cytologic diagnosis of Blastocystis hominis in peritoneal fluid: A case report

Background: Blastocystis hominis is the most common parasite identified in stool worldwide. Although it is commonly identified in stool preparations, it is unusual to encounter B hominis in abdominal fluid. Case: A 46-year-old woman presented with the clinical impression of acute peritonitis. The initial radiologic evalua tion showed free air in the abdominal cavity and an abdominal mass. Abdominal fluid submitted for cytologic examination was diagnostic of acute inflammation with mixed bacteria and abundant cystlike forms of B hominis. The patient underwent an exploratory laparotomy that revealed a poorly differentiated adenocarcinoma involving her bowel and peritoneum. Conclusion: The present case highlights the unusual identification of extraintestinal forms of B hominis in a peritoneal fluid sample from a patient with invasive, poorly differentiated adenocarcinoma and associated bowel perforation.