Hemorrhagic proctitis is a rare, but severe complication of radiation therapy in the treatment of several pelvic malignancies. Administration of topical steroids, anti-inflammatory agents or laser therapy and rectal instillation of 4% formalin have been described as a method of treating this complication. A dog model was established to study the safest volume and duration of administration of formalin, the histological changes in the rectal mucosa, and rectal compliance following this treatment.
Method: Twenty-one mongrel dogs were assigned randomly to seven groups. Three dogs received a rectal formalin bolus of 400 ml for 1 h; in the other six groups formalin was instilled in 30 ml aliquots to a total volume of 400 ml. Serum levels of formalin were obtained at designated time intervals, rectal compliance was evaluated pre- and post-formalin instillation, and rectal mucosa was analyzed for blood-vessel density and mucosal injury at different time points.
Results: Serum formalin in the bolus group reached toxic levels, while sequential instillation caused no serum toxicity in any dog. Rectal compliance and mucosal thickness were not affected by formalin, but there was a decrease in the angiogenesis score, and mild proctitis was seen in the acute and 1-week group.