- A case of intraabdominal giant cystic lesion that raised concern for pseudomyxoma peritonei preoperatively is presented here. A young woman underwent work-up for abdominal distension. Abdominal computed tomography suggested a diagnosis of pseudomyxoma peritonei. However, cystic degeneration of a giant myoma was found at surgery. There was no evidence of malignancy on histopathologic examination. This case illustrates that giant cystic lesions can mimic mucinous adenocarcinoma and pseudomyxoma peritonei.