Mucinous Adenocarcinoma Arising from Perianal Fistulae in Crohn’s Disease: A Rare Case Report and Review of the Literature

Abstract

Perianal fistula is a common manifestation of Crohn's disease. Adenocarcinoma arising from perianal fistulae in patients with Crohn's disease is rare. There are only 65 cases in English literature with anorectal adenocarcinoma arising from a perianal fistula in patients with Crohn's disease reported from January 1946 until September 2009. We present a case of 44 year old male diagnosed with Crohn's disease in 2012. Patient presented with worsening perirectal fistulas and posterior anal mass in 2014. Biopsy of posterior anal mass and right lateral anal margin, revealed mucinous adenocarcinoma. Given the findings of a perianal adenocarcinoma and extensive perianal Crohn's disease, the patient underwent neoadjuvant treatment, followed by abdominoperineal resection. Tumor size was 4.0 cm, estimated, as a discreet mass was not seen. This moderately differentiated adenocarcinoma was arising from the lining of the perianal fistulae tracts. The malignant cells and mucinous pools were diffusely involving the anal canal and part of the perianal fibroadipose tissue. The tumor demonstrated irregularly shaped tubules lined by cells with basally located, uniform, and hyperchromatic nuclei with abundant mucinous cytoplasm. The positive staining with CK20 and CDX2 in the tumor cells by immunohistochemistry suggests that tumor originated from colonic epithelium lining the fistula tracts. This case is unusual because of the very short duration between the first time diagnosis of Crohn's disease and development of adenocarcinoma in the perianal fistula tracts.