Colloid carcinoma arising in chronic anal fistula.

Mucinous carcinoma arising in chronic anal fistula is a rare but grave complication. Some sixty-five cases are reported in the literature. One additional case in a fistula of 47 years' duration is herein reported. The neoplastic glandular epithelium may arise from the rudimentary anal ducts or the bowel mucosa. Direct invasion occurs along the fistulous tract or adjacent tissues. Numerous cystic cavities filled with mucus are formed in the center of the process while an inflammatory reaction of the host tissue is provoked at the periphery. Hence biopsy material from the center of the process is more likely to be accurate than material from the periphery. MALIGNANT DEGENERATION IN A CHRONIC ANAL FISTULA SHOULD BE PROGRESSIVELY SUSPECTED UNDER THE FOLLOWING CONDITIONS: Excessive induration, recurrent postoperative induration, the discharge of mucus from a tract and the findings of mucusfilled cystic cavities at surgical excision.