An Uncommon Diagnosis Mimicking Peritoneal Carcinomatosis

Abstract

Peritoneal carcinomatosis is a term that characterizes the presence of extensive metastasis inside the peritoneal cavity, usually spread from a near-by primary malignancy. This diagnosis is associated with a grim prognosis, indicating intraperitoneal seeding or haematogenous dissemination from several types of tumors, including gastric, ovarian, pancreatic and colorectal cancers. There are, however, multiple non-neoplastic disease processes that can imitate peritoneal carcinomatosis on high-grade imaging. Our case presentation illustrates a rare and benign differential diagnosis in a patient who exhibited findings suspicious for peritoneal metastases with malignant ascites. A 79 year-old male with a PMH of DM, COPD, and BPH presented to the ER with the chief complaint of abdominal pain, distention, nausea, and malaise. He admits that the abdominal pain has been intermittent over the past 3 months and increasing severity. He admitted to a laparoscopic robotic singlesite cholecystectomy performed 7 months prior to this admission. A colonoscopy and endoscopy 1 year prior to this admission was normal. Abdominal CT demonstrated ascites and seven enhancing peritoneal lesions resembling implants. Abdominal MRI confirmed the findings. Paracentesis removed 2500ml of clear fluid, but cytology was non-diagnostic. A diagnostic laparoscopy found a 1.5cm abdominal wall nodule that was adherent to the anterior abdominal wall; no other peritoneal implants could be visualized. The liver appeared normal and there were no other gross abnormalities. Pathology of the lesion demonstrated granulomatous inflammation with fibrosis, with pigmented material resembling bile or a gallstone. Follow-up with the patient 2 weeks later demonstrated resolution of the ascites and abdominal pain. This case represents an extremely uncommon etiology of findings that were initially suspicious for peritoneal metastases. After thorough literature review, an explanation for this finding includes the spillage of bile during his laparoscopic cholecystectomy, which triggered an inflammatory response to the bile deposits trapped inside the peritoneum, mimicking the nodular implants of peritoneal carcinomatosis seen on computed tomography and magnetic resonance imaging. However, it is unclear why this occured in this patient specifically. Lingering questions include the possibility of genetic predisposition, the possibility of infection leading to an abnormal immune response resulting in granuloma formation, and the possibility of an existing disease such as Wegener's granulomatosis which lead to these findings. To conclude, a vast array of disease processes, including benign pathology, can mimic peritoneal carcinomatosis on imaging; thus, obtaining biopsies with appropriate histopathology and microbiology is vital in clenching the final diagnosis.