Idiopathic prolapse of 1 uterine horn in a yearling filly

Abstract

A yearling filly was presented for protrusion of a mass at the vulvar margins. A diagnosis of prolapse of the right uterine horn was made after vaginoscopy, transrectal palpation, and ultrasonography. It was confirmed later by biopsy of the tissue. Recovery was uneventful after easy replacement of the uterine horn.

A 330-kg, yearling Canadian filly was admitted to the Veterinary Teaching Hospital of the University of Montreal for protrusion of a tissular mass at the vulvar margins. She was presented in good body condition, with no history of medical problems; she was kept in a pad-dock with a 6-month-old colt. Despite a 9-hour-long transport, the filly looked bright and alert, without any clinical abnormalities other than a 20-cm long brownish and congested piece of tissue protruding from the vulvar lips. Results from a hematologic analysis revealed a marginal leukocytosis (12.6 × 10⁹ cells/L, reference range: 5.5 to 12.5 × 10⁹/L) and neutrophilia (9.5 × 10⁹ cells/L, reference range: 2.7 to 6.7 × 10⁹/L), and from a biochemical analysis were within normal limits.

Given the age of the filly and history, the differential diagnoses included laceration or hematoma of the vagina or vestibule, embryonic remnants, vaginal or cervical hyperplasia, uterocervical leiomyoma, and vaginal or uterine prolapse.

On vaginal palpation, the cylindrical mass of tissue was soft and relatively flaccid and could be felt coming through the cervix. The vaginal mucosa appeared normal and was without any palpable lesion. An endoscopic examination of the vagina confirmed that the mass was coming through the cervix and showed that its surface was edematous and congested. On transrectal palpation, the left ovary and uterine horn were easily localized, but the right ovary could not be palpated and the right uterine horn appeared to be shorter than the left one. The uterine body felt firmer and contiguous with the mass in the vagina. On transrectal ultrasonographic examination, the ovarian extremity of the right uterine horn was observed to be folded within itself, resulting in a structure of increased thickness. A portion of the right horn could also be seen projecting into the uterine body and the vagina. A preliminary diagnosis of right uterine horn prolapse was made. Biopsies of the mass were taken to rule out other conditions.

The filly was sedated by administering romifidine (Sedivet; Boehringer Ingelheim, Burlington, Ontario) 10 mg, IV, and butorphanol tartrate (Torbugesic; Wyeth Animal Health, Guelph, Ontario), 6 mg, IV. The prolapsed mass was easily and rapidly reduced manually. An endoscope was reintroduced into the vagina and passed through the cervix into the uterus to confirm reduction of the mass; some flaccidity of the whole genital tract was observed. Abdominal ultrasonography and a paracentesis for fluid analysis could not be performed, despite further heavy sedation, due to the refractory nature of the filly. The filly was placed in a box stall, treated with oral trimethoprim sulfadimethoxine (Novo-trimel DS; Novopharm, Toronto, Ontario), 30 mg/kg body weight (BW), PO, q12h, for 10 d, and monitored for the next 24 h, during which all vital parameters remained normal. The following day, an endoscopic examination of the vagina was repeated, which confirmed the absence of any abnormal mass in the vagina. Palpation of the vagina revealed an enhanced tone of the cervix and uterine body, compared with the previous day. The owners were informed of the possibility of a recurrence of the prolapse and of the risks of metritis, adhesions, peritonitis, and a decrease in fertility. They were also advised to keep the filly alone in a small box stall to prevent any effort that could increase the intraabdominal pressure. Because of financial constraints, the filly was discharged with a 10-day course of oral trimethoprim sulfadimethoxazole (Novo-trimel DS; Novopharm), 30 mg/kg BW, PO, q12h.

Histological examination of the samples of the mass confirmed that it was endometrial tissue, with congestion and superficial hemorrhage but without neoplastic cells in stratum spongiosum and stratum compactum. The diagnosis of prolapse of the right uterine horn was, therefore, confirmed.

To our knowledge, uterine prolapse has never been reported in nulliparous mares. It is an uncommon condition in the mare (1,2), occurring shortly following parturition and it has been reported sporadically as isolated cases (3,4). Uterine prolapse can occur in young primiparous as well as in old pluriparous mares; it might be predisposed by long mesometrial attachments; a relaxed or flaccid uterus; retention of the placenta at the ovarian pole in the nongravid horn (1,2); an increase in intra-abdominal pressure due to cribbing (4), straining or tenesmus (1,2), or colic (3); and labored foaling or obstetrical manipulations (2). Interestingly, one author reported a case of prolapse of the nongravid uterine horn in an 18-year-old pregnant mare examined for colic, 3 wk before term (3). Uterine prolapse can be complicated by endotoxemia or septicemia and can lead to fatal intra-abdominal hemorrhage if the enlarged uterine vessels rupture (1,2). Invagination of the uterine horn is reported to occur in the cow and mare (2). In the present case, the filly was prepubertal, so the lack of hormonal effect on the uterus could explain its flaccidity. Also, the absence of vascular development of the broad ligament compared with that of the postpartum mare could explain the good prognosis, despite the time the filly spent before her arrival at the reference center.

Uterine prolapse is a relatively common condition in the postpartum dairy cow, generally associated with hypocalcemia and dystocia (2), and in the pluriparous postmenopausal woman (5). This condition is also well recognized in neonates and young nulliparous women (5,6). In 1723, Conovius described the first case of genital prolapse in a newborn (5). The main predisposing factors recognized in women are sacral innervation deficits and malformation or acquired weakness of the supportive pelvic structures, in association with an increased intra-abdominal pressure caused by crying (6), straining (7), laughing, coughing, or sneezing (5). Numerous neurological and spinal abnormalities may also be associated with uterine prolapse in the neonate: Spina bifida, present in 86% of the neonatal uterine prolapses in Findley’s review (7); meningomyelocele (6); and other conditions such as hydrocephalus, spastic or paretic lower extremities, scoliosis, kyphosis, lordosis (6,7), club feet (6), genurecurvatum (6), as well as pelvic skeletal deformities and abnormalities of the uterus, cervix, or vagina (5,6). However, cases of uterine prolapse without developmental defects have also been reported in neonates (6) and in young nulliparous women (7). Birth trauma in the case of neonates and hard labor, persistent coughing associated with poor nutrition (7), and strenuous activity (airborne training) in presence of uterine nerve ablation (8) in the case of young nulliparous women have been proposed as the cause of the uterine prolapse.

In the mare, the reproductive tract extends from the level of the 4th or 5th lumbar vertebra to the vulva; it is suspended cranially by the broad ligament, which is particularly long in this species and consists of the fusion of 2 peritoneal sheets (mesometrium) extending along lateral sublumbar and pelvic walls (9). Lymphatic vessels, loose collagenous and adipose tissues, and sheets of smooth muscle continuous with the outer muscular layer of the uterine tube and uterus are contained between the 2 layers of the broad ligament, which becomes continuous with the lateral ligaments of the bladder (9). The broad ligament attaches to the dorsal aspect of the uterus and cervix (9). The vagina and its vestibule are covered by a loose collagenous connective tissue adventitia, adipose tissue, a venous plexus, and the vestibule constrictor muscle, arising from the levator fascia and the lateral edges of the perineal septum, covers the lateral and ventral aspects of the vestibule (9). Innervation of the ovaries, uterus, and vagina is supplied by the renal, aortic, uterine, and pelvic plexuses, while the vestibule, the vulva and its muscular structures are innervated by the pudendal and caudal rectal nerves (9). The sensory innervations of the vulva, vagina, and vestibule were considered normal in this case, as the filly resented manipulation of these structures. As the sensory innervation may be conserved in lower motor neurone diseases, a sacral innervation deficit cannot be ruled out in the present case despite a lack of other neurological signs. Examination of the filly’s genital tract after resolution of the invagination of the uterine horn revealed only a relaxed cervix, without structural abnormalities. The broad ligament was impossible to palpate, and we speculated that it could be abnormally soft or had been elongated. Because the filly was in excellent body condition and there was no history of coughing, straining, or colic reported by the owners or observed during hospitalization, we hypothesized that lack of uterine tone due to the absence of hormonal influence on the uterus may have caused the prolapse of the uterine horn. Nerve dysfunction is another potential factor causing lack of muscle tone of the genital tract in the present case.

The differential diagnoses of abnormal genital masses in nonpregnant mares includes uterine neoplasia, embryologic remnants, and cervical hyperplasia (10). Uterine neoplasia is extremely rare in mares, as only 27 cases of uterine tumor in mares were recorded in 20 American colleges of veterinary medicine in 20 y (11). Leiomyomas, rhabdomyosarcomas, carcinomas, and cervical cysts have been reported (11,12). Embryologic abnormalities, such as mesonephric or Wollfian duct cysts in the vaginal floor or uterine horn, segmental aplasia of 1 of the mesonephric ducts resulting in a missing cervix and small uterine horn, and uterus bicollis, are also rare.

As evidenced in this case and despite its probably rare occurrence, uterine or uterine horn prolapse should be included in the differential diagnoses of abnormal masses of the genital tract in prepubertal mares. CVJ

Figure 1.

The brownish, edematous mass protruding through the vulvar lips of the yearling filly at admission.