The occurrence of black pigmentation in the peritoneal cavity is rare, and its rapid clinical diagnosis may be difficult. Here, we report a case with pigmented peritoneal deposits diagnosed via a histopathological examination at postoperative period. A 74-year-old woman was diagnosed with stage 2 pelvic organ prolapse on the POP-Q system, and planned to undergo a laparoscopic sacrocolpopexy. She had an obstetric history of two uncomplicated vaginal births, and a medical history of colon cancer. During the surgery, variously sized, irregularly shaped and partially swollen black pigments were observed mainly in the small pelvic cavity. Because malignant melanoma dissemination was suspected by macroscopic findings, sampling tissues were submitted to the rapid histopathological examination with frozen sections. However, the histopathological examination could not rule out malignancy because of the presence of cell nests similar to melanocytes with large nucleoli. Thereafter, to prevent the spread of the suspected cancer cells, the surgical procedure was switched to a vaginal approach. No malignant lesions were observed in a whole-body examination performed after the operation. Additionally, immunohistochemistry showed no evidence of malignancy or atypia in black pigmented tissues. When we checked the colon cancer operation records and pictures at 5 years ago, it was revealed that the black pigments were markings painted during this surgery. The present case serves as a reminder for differential diagnosis of black pigments in the abdominal cavity.
