Although vaginal hyperplasia and vaginal prolapse are terms often used interchangeably to describe protrusion of a donut, ball or tongue-shaped mass from the vulva, there are subtle differences between the two conditions.
Vaginal hyperplasia occurs during the follicular phase (maturing of ovary) of the estrus cycle. During this phase, vaginal and vulvar mucosa becomes edematous (swollen) in response to high estrogen levels. Exaggeration of this response causes excessive mucosal folds from the vaginal floor to protrude through the vulvar labia, resulting in protrusion of a tongue or ball-shaped mass.
In other words, Vaginal hyperplasia is an exaggerated swelling reaction of the vaginal tissue to estrogen during the proestrus and estrus phases of heat. Should the swollen vaginal tissue become too swollen and no longer be contained within the vagina, it may bulge out, appearing as a tongue shaped mass, through the vulva, which is the external female genital organ. The mass may prevent the dog from mating
Vaginal prolapse, on the other hand, is the protrusion of the entire circumference of the vaginal wall, including the urethral papillae, through the labia.
In other words, Vaginal prolapse is the protrusion of swollen vaginal tissue through the vulva, the external female genital organ, during the heat cycle. In vaginal prolapse, the swollen protruding vaginal tissue may resemble that of a donut shaped mass.
The two conditions can occur in any dog but young intact female dogs of certain breeds are at a higher risk. These breeds include Labrador and Chesapeake Bay retriever, boxer, English bulldog, mastiff, German shepherd dog, St. Bernard, Airedale terrier, Springer spaniel, Walker hounds, and Weimaraner.
The conditions can be classified into types. Type 1 hyperplasia occurs when the protrusion is slight and does not exit the vulva itself. Type 2 hyperplasia, on the other hand, is when the vaginal tissue actually protrudes through the vulvar opening. While Type 3 hyperplasia refers to the donut-shaped mass, which can be seen externally.
The principal sign is the protrusion of a tongue-shaped mass through the vulva. Other signs include painful urination, unwillingness to copulate and excessive licking at the vulva.
Dystocia (abnormal or difficult labor), tenesmus (straining) associated with constipation or difficult urination, or forced extraction of the male during the genital tie (intercourse) are all thought to cause or contribute to vaginal prolapse.