Implantation Of Sigmoid Adenocarcinoma Into Intersphincteric Anal Fistula Detected Three Months After Anterior Resection

Adenocarcinomas associated with perianal fistulas are very uncommon. Two different pathological pathways have been described to underlie their development. The more commonly described pathway relates to a chronic inflammatory process and subsequent dysplasia in the absence of any associated colorectal malignancy. The second –and much more uncommonmechanism results from the implantation of viable exfoliated tumour cells from a synchronous remote colorectal cancer. We report the case of a 68 year old man who had an adenocarcinoma identified in a perianal fistula three months after a high anterior resection performed for a pT3 N0 sigmoid adenocarcinoma. Pathological assessment of this deposit revealed that this had identical tumour characteristics to his original sigmoid adenocarcinoma confirming that exfoliated viable malignant cells had likely become implanted in a pre-existing clinically dormant perianal fistula.