Leiomyoma is a benign smooth muscle tumor of the vulva (entrance to the vagina) or vagina. The tumor may exist as extraluminal, a slow growing perineal mass or intraluminal which is attached to vestibular or vaginal wall. There can be multiple intraluminal masses of varying size and may be seen protruding through the vulva. Ulceration can occur with exposure and irritation. This tumor is also thought to be hormone dependent since recurrence occurs in about 15% of dogs left intact and does not recur at all in dogs that are spay at the time of tumor removal.
Mean age of occurrence is about 11y old and Boxers are predisposed. About 1/3 of female dogs with leiomyoma may have associated endometrial hyperplasia, ovarian cyst and/or mammary gland tumors. Clinical Signs
The mass may protrude from the vulva. The dog may strain when urinating, blood may be present in the urine, there may be vulvar discharge and vaginal bleeding. Masses may also cause secondary bacterial vaginitis, obstruction to surrounding structures, patient may have trouble defecating, and perineal swelling. If masses compress and/or irritate the rectum, heavy mucus production may be noticed from the anus. Compression or obstruction of the lymphatics or veins can result in rear limb edema and lameness. Pain can be severe or absent.
Diagnosis
The mass is often seen protruding from the vagina or around the rectum. Digital and/or vaginoscopic examinations often reveal the extent of the mass, but occasionally retrograde vaginography, urethrocystography, or ultrasonography may be necessary to delineate the mass. Fine needle aspirate may diagnose some tumors such as transmissible venereal tumors. Histopathology is recommended so that appropriate prognosis and treatment are given.

Treatment and Prevention
Surgical excision is the recommended treatment for this type of vaginal tumors. Episiotomy must be performed for full exposure of the mass to ensure its removal. It is important to catheterize the bladder in order to know where the urethra is and to protect it during surgery. Since these tumors are thought to be hormone dependent ovariohysterectomy (OHE) should be performed concurrently. Prognosis is good with complete resection and OHE. Spaying your pet by 6 months of age is the best prevention.