Fibromatosis in vertical rectus abdominis myocutaneous flap imitating tumor recurrence after surgery for locally advanced rectal cancer: case report

BACKGROUND: Abdominoperineal excision is performed in patients with locally advanced, low rectal carcinoma. Reconstruction of the dorsal vagina and perineum using the vertical rectus abdominis myocutaneous flap following extensive surgery results in favorable surgical outcome and quality of life. However, the rectus abdominis muscle, as part of the anterior abdominal wall, may develop fibrous lesions also as a transplant. CASE PRESENTATION: A 39-year-old female patient with low rectal cancer and extensive colorectal polyposis was treated with neoadjuvant chemoradiotherapy followed by colectomy and abdominoperineal excision with resection of the dorsal vaginal wall and subsequent reconstruction of the perineum using the vertical rectus abdominis myocutaneous flap. At the 6-month follow-up, a suspected 2 × 2 cm tumor recurrence was detected in the transposed tissue and was subsequently surgically removed. Histologic examination concluded with fibromatosis. Genetic testing revealed a known disease-causing mutation in the adenomatous polyposis coli gene, confirming the diagnosis of familial adenomatous polyposis. CONCLUSIONS: Fibromatosis may affect the anterior abdominal wall, that is the rectus abdominis muscle, at the primary site or may develop in the muscle after its transposition into the perineum at pelvic reconstruction. Fibromatosis in the muscle flap after pelvic reconstruction may present a difficult diagnostic challenge for the multidisciplinary team.