[Atresa ani and rectocutaneous fistula in an adult guinea pig (Cavia porcellus)].

A 4-year-old, male guinea pig in a good general condition was presented for a routine castration. Since its birth, the animal had been kept outdoors with a male sibling. At the initial examination the perineal sac was smaller compared to other intact male guinea pigs. At the caudal end of the perineal sac a small dimple was noted, that ended blindly after 3mm. The following examination under anaesthesia revealed a fistula opening 1cm caudodorsally to the anus. The skin around the opening was bulging but without any signs of inflammation. Slightly protruding and reddened mucosa was visible inside the opening. After instillation of a contrast agent into the fistula a radiograph showed a contrast-filled caudal region of the large intestine. The intestine appeared to be normal and no other abnormalities were present. The excretion of normal faeces through the fistula was visible and atresia ani with a rectocutaneous fistula was diagnosed. The examination of the male sibling showed a normally developed anus. As the guinea pig had no clinical signs or associated malformations apart from the smaller perineal sac and the passage of normal faeces was possible through the fistula opening, no therapy was scheduled. To the authors' knowledge, this is the second report of this congenital abnormality in a guinea pig. The characteristics of this case include the high age of the animal at diagnosis of the atresia ani, the gender and the formation of a single rectocutaneous fistula.