In dogs, the muscles of the pelvic diaphragm can weaken and separate from the rectum, resulting in a perineal hernia. The cause of this muscle weakening is unknown, but as the condition is seen most commonly in older, entire male dogs, a hormonal cause is suspected. In addition, any condition that causes straining to go to the toilet (for example, prostatic disease) or which increases intra-abdominal pressure (for example, pregnancy) can cause a perineal hernia.
A perineal hernia leads to loss of support to the rectal wall, resulting in difficulty going to the toilet, and risks the herniation of intra-abdominal contents such as the urinary bladder. While perineal hernias can be one-sided, frequently left and right (bilateral) hernias occur.