A case report of anal fistula-associated mucinous adenocarcinoma developing 3 years after treatment of perianal abscess

Abstract

Background: A long-standing (over 10 years) anal fistula is considered a fundamental cause of fistula-associated mucinous adenocarcinoma (FAMC). Perianal abscesses and anal fistulas are two sequential phases of the same anorectal infectious process. We experienced a case of FAMC which developed 3 years after the treatment of a perianal abscess.

Case presentation: A 68-year-old woman was admitted to our hospital because of progressive anal pain and a palpable tumor. She had a history of undergoing a drainage operation for a perianal abscess 3 years previously. A 15 × 15-mm tumor at the former drainage site was identified; transanal ultrasonography showed an intersphincteric fistula connecting to the tumor. A biopsy taken from the tumor demonstrated mucinous adenocarcinoma; the tumor was diagnosed as FAMC. Laparoscopic abdominoperineal resection was performed. Histopathology showed highly dysplastic cells lining the lumen of the anal fistula and poorly differentiated mucinous adenocarcinoma proliferating in the dermis and epidermis in the distal aspect of the fistula.

Conclusions: FAMC can develop within fewer than 3 years after the development of a perianal abscess and anal fistula.

Keywords: Anal carcinoma; Anal fistula; Carcinogenesis; Cryptitis; Cryptoglandular infectious theory; Dysplasia; Fistula-associated mucinous adenocarcinoma; Perianal abscess; Transanal ultrasonography.

Fig. 1

Imaging studies. a Transanal ultrasonography revealed a fistula-like structure with unclear boundaries in the intersphincteric layer at the time of the perianal abscess 3 years previously (arrow). b Anal fistula was expanded with hypoechoic content at the time FAMC was diagnosed. c [18F]-Fluoro-2-deoxy-d-glucose (FDG)–positron emission tomography/computed tomography showed lymphadenopathy in the right internal iliac and inguinal regions with abnormal FDG accumulation (arrows)

Fig. 2

Preoperative photograph. The tumor was observed at the 5 o’clock position, corresponding to the drainage site for the perianal abscess

Fig. 3

Image of the resected specimen. The secondary opening of the fistula was obscured, because it was involved in the tumor. The yellow bar indicates a cross section of the pathological image

Fig. 4

Histopathologic photographs, hematoxylin and eosin (H&E) staining. a Lumen of the fistula (*) is expanded with a massive mucinous component. Carcinoma cells invade the dermis and epidermis around the distal site of the fistula (×40). b Mucin-containing poorly differentiated adenocarcinoma is present (×100). c Highly dysplastic epithelial cells lined the lumen of the anal fistula (×100)