Equine Uterine Tear Study Guide

Overview and Clinical Importance

Uterine tears are among the most serious periparturient emergencies in broodmares, representing one of the leading causes of postpartum peritonitis and mare mortality. Understanding the recognition, diagnosis, and management of uterine tears is essential for NAVLE success and clinical practice.

Among postpartum deaths in mares, uterine tears account for approximately 6% of mortality, making them the third most common cause of death after ruptured uterine artery (40%) and cecal perforation (19%). In referral populations, uterine tears are diagnosed in approximately 5.5% of postpartum emergency cases.

Anatomy Review

Mare Uterine Anatomy

The equine uterus is bipartite and T-shaped, consisting of two uterine horns (approximately 20-25 cm each) that fuse into a relatively large uterine body (18-20 cm). The uterus is suspended within the abdominal cavity by the broad ligaments (mesometrium), which attach to the dorsal aspect of the uterus. This dorsal attachment means the free (unattached) surface of the uterus is ventral.

The uterine wall consists of three layers: the endometrium (innermost glandular layer), myometrium (muscular layer with inner circular and outer longitudinal fibers), and perimetrium (outer serosal layer continuous with the broad ligament).

Etiology and Pathophysiology

Causes of Uterine Tears

Uterine tears can occur through several mechanisms. Spontaneous tears develop during normal parturition (stage II labor) due to violent movement of fetal hindlimbs within the pregnant horn. Despite protective gel-like "slippers" covering fetal hooves in utero, rapid extension of the hindlimbs as fetal stifles pass through the pelvis can cause laceration.

Iatrogenic tears result from fetal manipulation during dystocia correction or fetotomy. High-risk malpresentations include ventro-vertical presentation with hip flexion ("dog-sitting posture"). Other iatrogenic causes include perforation during uterine prolapse replacement or aggressive uterine lavage in mares with friable, inflamed endometrium following dystocia.

Classification of Uterine Tear Causes

Anatomic Location of Tears

Research demonstrates that uterine tears occur significantly more commonly in the right uterine horn than other locations (P=0.018). Tears most commonly occur in the pregnant horn, especially at the tip. The dorsal aspect of the uterus is another common site, particularly for spontaneous tears occurring during normal delivery.

Clinical Presentation

Timeline and Signs

Mares with uterine tears typically present 1-6 days after parturition, with most presentations occurring within 2-3 days post-foaling. A critical point is that signs may not be evident until 24-48 hours after parturition, making early detection challenging.

Clinical Signs of Uterine Tear

Diagnosis

Diagnostic Approach

Diagnosis of uterine tears can be challenging due to the large size of the postpartum uterus and pronounced endometrial folds that can conceal small or partial-thickness tears. Most uterine horn tears are beyond reach via transrectal or transvaginal palpation.

Laboratory Findings

Leukopenia is strongly associated with uterine tear diagnosis. While mares may initially show leukocytosis and neutrophilia with left shift on the day of delivery, this is followed by marked leukopenia and neutropenia by day 3 post-parturition, persisting to day 5. Circulating neutrophils frequently demonstrate toxic changes on cytology.

Abdominocentesis Findings

Important: Normal parturition and even prolonged obstetrical manipulations do NOT change the peritoneal fluid profile from normal. Therefore, abnormal peritoneal fluid in a postpartum mare is clinically significant.

Imaging Findings

Transabdominal ultrasonography may reveal increased quantities of abdominal fluid with increased echogenicity and fibrin tags suggestive of peritonitis. Immediately after foaling, ultrasound may show no abnormalities, but changes develop over 24-48 hours.

Differential Diagnosis

Postpartum mares presenting with colic and systemic illness require consideration of multiple differentials, as the signs can overlap significantly.

Treatment

Treatment of uterine tears can be medical or surgical, and research demonstrates that survival rates are similar between treatment modalities. The choice depends on tear characteristics, mare condition, and available resources.

Medical (Conservative) Management

Conservative management may be successful if the tear is small, located on the dorsal aspect of the uterus, associated with minimal hemorrhage, and no uterine therapy is required. Medical treatment is as expensive as surgical treatment in many cases.

Medical Treatment Protocol

Surgical Treatment

Early surgical intervention aids in definitive diagnosis, detection of concurrent pathology, and repair of the uterine defect. Exploratory celiotomy allows direct visualization and repair of tears, as well as abdominal lavage for peritonitis management.

Surgical approaches include ventral midline celiotomy under general anesthesia. The uterus is exteriorized, the tear is identified and debrided, and primary closure is performed. Peritoneal lavage with large volumes of sterile isotonic fluids is typically performed.

Prognosis

Prognostic Indicators

The interval from occurrence to diagnosis and treatment initiation has a significant impact on prognosis. The sooner diagnosis is made, the better the outcome.

Memory Aid

UTERINE TEAR = T.E.A.R.S. T - Time matters (early diagnosis improves prognosis) E - Equally likely with or without dystocia A - Abdominocentesis shows septic peritonitis R - Right horn most common location S - Survival 81% with surgical treatment

Complications

Regardless of the cause of uterine rupture, contamination of the abdominal cavity with blood and intrauterine contents causes septic peritonitis. If left untreated, this results in endotoxemia with potential sequelae including laminitis (which can progress rapidly to founder), multiple organ dysfunction, and death.

Visceral herniation through the uterine defect is a serious complication that may be detected if abdominal viscera are found in the birth canal during postpartum examination.

Future Fertility

An encouraging finding for owners is that mares that survive uterine tears may successfully maintain pregnancies afterward. Studies show that 77% of mares bred the subsequent year after surgical treatment carried a foal to term. Importantly, recurrence of uterine tears has not been observed in surviving mares.