Clinics in diagnostic imaging (143). Perianal mucinous adenocarcinoma arising from chronic fistula-in-ano.

We report a case of mucinous adenocarcinoma arising in the perianal soft tissue in association with chronic fistula-in-ano in a 43-year-old man who had a relapse of perianal pain and bloody discharge after six years of defaulted follow-up. He underwent magnetic resonance (MR) and computed tomography imaging with correct identification of the disease entity on imaging. Mesh-like septations and an enhancing solid component with high diffusion-weighted imaging (DWI) and intermediate apparent diffusion coefficient signals were observed. He underwent abdominoperineal resection of the tumour but succumbed due to postoperative complications. Literature on the MR imaging features of this tumour remains scarce. We highlight the MR imaging features, including those seen on DWI, which were useful in making the correct diagnosis. Though uncommon, this would be an important condition to recognise since assessment of fistula-in-ano by MR imaging is considered to be the standard of care in current clinical practice. The clinical features of this entity are also briefly discussed.