Metastatic Anal Fistula Carcinoma after Rectosigmoid Cancer Surgery Treated with Robot-Assisted Abdominoperineal...

Robot-assisted surgery has become an established approach for rectal cancer, offering favorable short-term outcomes and oncologic results comparable to conventional laparoscopic surgery. With recent technological advances, its use has expanded to more complex scenarios, including reoperative surgery with severe adhesions or distorted pelvic anatomy. Metastatic anal fistula carcinoma is uncommon, and its surgical management is challenging, particularly in patients with prior rectal surgery because of severe adhesions and distorted pelvic anatomy. We report a rare case of metastatic carcinoma associated with an anal fistula that developed after curative resection of rectosigmoid cancer and was treated with robot-assisted abdominoperineal resection (R-APR) and gluteal myocutaneous flap reconstruction.

A 61-year-old man who had previously undergone laparoscopic high anterior resection for Stage IIIB rectosigmoid cancer presented 13 months later with anal pain and swelling. Imaging revealed a mass connected to the rectum through a chronic fistulous tract, and biopsy confirmed adenocarcinoma. A primary carcinoma arising in an anal fistula or local recurrence of rectosigmoid cancer was considered. R-APR was performed using the da Vinci Xi system. Severe adhesions around the prior anastomosis were meticulously dissected, allowing safe total mesorectal excision and resection of the tumor and fistula tract. The large perineal defect was reconstructed with bilateral gluteal myocutaneous flaps. No intraoperative complications occurred. Histopathological examination showed an adenocarcinoma that was morphologically identical to the previously resected rectosigmoid cancer with no evidence of associated in situ lesions. In addition, both tumors demonstrated CK7 (-)/CK20 (+) staining on immunohistochemical examination, which is most consistent with metastatic anal fistula carcinoma. Surgical margins were negative, and no recurrence was observed during 12 months of follow-up.

This case suggests that the robotic platform may facilitate safe dissection in complex reoperative pelvic procedures. Gluteal myocutaneous flap reconstruction provided effective coverage for a large perineal defect in this patient.