Perineal swelling from lipoleiomyoma in 4-year-old Huntaway dog

Abstract

CASE HISTORY: A marked perineal swelling was identified in a 4-year-old entire nulliparous Huntaway bitch. The mass was first observed at last oestrus, 6 months previously. CLINICAL FINDINGS: A diffuse swelling was visible in the perineum that extended from the anus to the vulva. The vulval commisure was distorted ventrolaterally. An extraluminal mass involved the vulva, vestibule and vagina. On rectal and vaginal examination the rostral extent could not be identified. There was no palpable intraluminal mass. The bitch produced a reduced urine flow, and there was complete voiding of the bladder. The urethra was not involved. Vaginal cytology suggested pro-oestrus. PATHOLOGICAL FINDINGS: Multiple fine-needle aspirates were non-diagnostic. Incisional biopsies revealed extensive well-differentiated fatty tissue with scattered bundles of collagen and occasional fascicles of smooth muscle. Following complete excisional biopsy the formalin-fixed neoplasm weighed 714 g and measured 13 x 11 x 6 cm. Histologically, there was a thin outer layer of fibrous tissue, surrounding sheets of mature adipocytes and randomly distributed bundles of smooth muscle. Immunohistochemical findings were consistent with a smooth muscle neoplasm possessing oestrogen receptors. DIAGNOSIS: The clinical, gross, histological and immunohistochemical findings were consistent with a diagnosis of lipoleiomyoma expressing oestrogen receptors. CLINICAL RELAVANCE: A lipoleiomyoma should be considered a differential diagnosis for a benign tumour in the caudal reproductive tract of the bitch. Incisional and fine-needle aspiration biopsies of a lipoleiomyoma may resemble a lipoma. Excisional biopsy may be required for a definitive diagnosis. Lipoleiomyomas in the reproductive tract of the bitch may possess sex steroid receptors, and patients may benefit from ovariohysterectomy or hormonal therapies prior to excision.