Uterine rupture (UR) is rarely diagnosed in dogs and cats (7,11) and can be attributed to various factors including external trauma, infections, torsion, improper obstetric techniques, excessive oxytocin administration, and abnormal fetal positioning (14). Most cases of UR are related to compromised uterine wall due to conditions such as endometritis, pyometra, intrauterine fetal death, uterine torsion, or prolapse (3).

Existing veterinary literature has reported that uterine rupture can also be caused by blunt or penetrating abdominal trauma in small animals, which can occur after motor vehicle accidents or bite injuries (6,8). Common internal abdominal injuries include liver or spleen damage, leading to hemoperitoneum, bladder, or diaphragmatic rupture, resulting in a diaphragmatic hernia (6,8). An enlarged uterus during late-term pregnancy is more vulnerable to injury due to trauma (3). In small animals and in the absence of prior hysterotomy incisional scar tissue, uterine ruptures primarily occur in a single uterine horn, whereas uterine ruptures commonly happen in the body of the uterus in humans because of differences in anatomical structure (10,11,15).

The present case report describes a rare case of incidental uterine horn rupture observed during elective ovariohysterectomy in a non-gravid small-sized dog with a history of diaphragmatic hernia caused by a traffic accident.

A 4-year-old intact female mixed-breed dog weighing 3 kg was referred to the Veterinary Medical Teaching Hospital of Chungnam National University from a local hospital with the chief complaint of dyspnea. This patient had a recent history of traffic accidents. Upon presentation, the patient presented with respiratory distress. Chest and abdominal radiographs confirmed that the abdominal organs, presumed to be the liver and small intestine, had herniated into the thoracic cavity, leading to a diagnosis of traumatic diaphragmatic hernia. Emergency herniorrhaphy was performed immediately, and the patient was discharged without any postoperative complications.

Two months after the initial surgery, the patient revisited our hospital for an elective ovariohysterectomy. The patient had a history of prolonged estrus (>one month’s duration). During estrus, a small amount of blood was discharged continuously from the vagina. There were no significant findings in the pre-anesthetic examination.

The patient was preoxygenated with 100% oxygen using a flow-by technique. Preanesthetic medication consisted of maropitant (1 mg/kg, SC; Cerenia, Zoetis, Spain) and cefazolin sodium (22 mg/kg, IV; Cefazolin, Jonggeundang ROK). Propofol (1 mg/kg, IV; Anepol, Hana ROK) and midazolam (0.2 mg/kg, IV; Midazolam Inj., Bukwang ROK) were administered slowly, followed by propofol (4 mg/kg, IV; Anepol, Hana ROK). Anesthesia was maintained using isoflurane (Ifran, Hana, ROK). Bupivacaine hydrochloride hydrate (0.2 mg/kg SC; Bupivacaine, Myungmoon ROK) was administered along the incision line for local analgesia.

After positioning the patient in dorsal recumbency, laparotomy was performed by incising the cranial third from the umbilicus to the pubis. A completely transected left uterine horn was observed during ovariohysterectomy (Fig. 1A). Each end of the uterine horn was connected by an intervening mesometrium. The transected parts of the uterine horn were spherical on both sides, the uterine layers were exteriorized, and the endometrium was observed outside (Fig. 1B). The uterine cavity was not opened at the end of the transection. No inflammation, fibrosis, or hemorrhage was observed around the transected uterine horn. There were no adhesions or strictures in the adjacent tissue. There were no gross abnormalities observed on the other abdominal organs, such as the ovaries or kidneys. After ovariohysterectomy, the abdomen was closed. The patient recovered well following surgery and was discharged the following day.

Figure 1. Intraoperative and macroscopic findings. (A) lntraoperative image of the transected left uterine horn. (B) Dome-shaped ends in the transected part of the uterine horn.

Macroscopic examination of the uterus revealed an abnormal closure of the tubular left uterine horn, isolating a proximal mucus-filled cavity adjacent to the left ovary. The diameter of the left uterine horn near the ovary was approximately 1.2 cm and 1.5 cm near the cervix. Mild cystic endometrial hyperplasia with viscid fluid was observed in both uterine horns. The excised organs were placed in formalin and submitted for histopathological analyses.

Histopathological examination of the transected left uterine horn revealed extrusion of the endometrium and extension from the uterine horn lumen, resulting in a dome-shaped end (Fig. 2A). All the layers of the uterine horn could be identified and were well differentiated on the cross section through the wall of the specimen, as observed with the normal uterine horn structure (Fig. 2B). The endometrial glands observed inside of the lumen were tubular in abundant stroma with densely packed glands (gland: stroma >1) (Fig. 2C). Similarly, irregular glands with variations in the shape and size were observed over the muscular layer (Fig. 2D). Cystic glands of various sizes were also present in the cuboidal epithelium. No nuclear atypia was observed and the nucleus-to-cytoplasm ratio was low. No mitotic activity was observed.

Figure 2. Histological images of the transected left uterine horn (hematoxylin and eosin staining). (A) Longitudinal left uterine horn fragment at the transected end. Proliferated and extended endometrium over the muscular layer (scale bar: 1.25 mm). (B) Transverse left uterine horn fragment at the transected end. Well-differentiated mucosa, submucosa, muscularis, and serosa layer (scale bar: 500 µm). (C) Endometrial glands observed inside the left uterine horn lumen (scale bar: 100 µm). (D) Irregular endometrial glands observed over the muscular layer showing variation in shape and size (scale bar: 100 µm).

Uterine rupture in small animals is rare in veterinary literature (3). The causes of uterine rupture in dogs and cats encompass various factors, including trauma, anomalies in uterine horn development, and pathological conditions like pyometra (4).

Although rupture of the gravid uterus is an uncommon finding in female dogs, it has been observed occasionally during the periparturient period, often in patients with dystocia, following cesarean section procedures, or in combination with pyometritis (7). Additionally, uterine rupture can result during post-partum in animals that were administered oxytocin or prostaglandins to induce labor or as a treatment for metritis or dystocia (4,13). Most cases of uterine rupture involve uterine wall compromise secondary to pathological conditions such as endometritis, pyometra, intrauterine fetal death, uterine torsion, or prolapse, which leads to structural weakness (3). Uterine rupture is highly associated with pregnancy-related factors, and trauma-induced uterine rupture is commonly observed in gravid animals.

The clinical signs of uterine rupture include abdominal swelling, abdominal pain, and changes in the patient’s condition, such as lethargy and anorexia (4,9). Uterine rupture often leads to fatal outcomes; however, most cases remain undiagnosed (5,7). A definitive diagnosis of uterine rupture can only be made using exploratory laparotomy (4). Notably, most case reports of uterine rupture in veterinary medicine have apparent clinical signs that are indicative of uterine rupture, affecting mostly gravid patients (4). In contrast, based on the information provided by the owner, the patient in the current report was not pregnant and showed no clinical signs suggestive of uterine rupture. Additionally, there were no significant findings on clinical examination or laboratory results.

In this case report, an asymptomatic uterine rupture is described in a patient who underwent elective neutering. While the exact cause of the uterine rupture in this case cannot be determined with certainty, it is highly suspected that the car accident that occurred two months prior was a major factor. When the cause of uterine rupture is traumatic, it is frequently associated with other injuries in different organs and is sometimes accompanied by diaphragmatic hernia (11). In this case, the patient had a history of a diaphragmatic hernia caused by vehicular trauma.

Discontinuity of the uterine horn can occur due to trauma but can also occur congenitally (12). Malformations of the Müllerian duct are the primary cause of congenital uterine abnormalities, which encompass conditions such as bilateral agenesis, unilateral agenesis including unicornuate and hemiuterus, and segmental aplasia (1). These congenital defects are often associated with hermaphroditic conditions or ipsilateral renal agenesis due to the close developmental connections between the urinary and genital systems (1).

In cases of segmental aplasia of the genital system, anomalies are apparent as missing segments or strictures that disrupt normal anatomical structure (2). These anomalies correspond to the incomplete development of all layers of the affected segment, often resulting in a rudimentary cord-like structure (2). However, in this case, there was no cord-like structure between the uterine horn segments, and the horns were completely disconnected. On histopathological examination, the mucosal, submucosal, muscular, and serosal layers could be differentiated. All the layers were distinct in gross appearance and histopathology, and differentiated well like a normal uterine structure, except for the transected portion of the left uterine horn. The mucosal layer appeared to be everted only at the transected left uterine horn. Numerous glandular structures in the mucosal layer were clustered at the distal end of the uterine horn. This appears to be a result of morphological changes associated with uterine horn rupture rather than being indicative of congenital developmental abnormalities. Furthermore, no morphological or functional abnormalities were observed in the ovaries or kidneys, which are typically observed in patients with congenital developmental uterine abnormalities. Cystic endometrial hyperplasia was observed in both uterine horns, which makes the uterine wall compromised, making it more susceptible to rupture from external trauma than a normal uterus. Therefore, it is more likely that the rare form of uterine abnormality observed in this case resulted from acquired factors, such as trauma, rather than congenital factors.

In the present case, uterine rupture was not detected immediately at initial presentation after the motor vehicle accident, but rather during the elective neutering of an asymptomatic, healthy patient. The absence of adhesions or fibrotic changes in the surrounding tissues during the neutering procedure and the lack of inflammatory cells on histological evaluation could potentially limit the diagnosis of trauma-associated uterine rupture.

Unlike in human medicine, ovariohysterectomy is routinely performed in veterinary medicine to treat reproductive organ diseases and control reproduction. No significant differences were observed between the surgical procedures used in the present case and those used to treat reproductive organ diseases in small animals. Therefore, uterine rupture can be treated with conventional ovariohysterectomy. Notably, when there is a clinical suspicion of uterine rupture, it is imperative to recommend surgical exploration because of severe and potentially life-threatening complications (3). It is crucial to consider that the clinical progression can vary from mild illness to rapid clinical deterioration and mortality (3).

This case report illustrates a rare case of a ruptured uterine horn in a dog, with no clinical signs of uterine rupture, observed prior to elective ovariohysterectomy. The uterine rupture was possibly a result of traumatic injury, considering the patient’s history, complete disconnection of the uterine horn, and the lack of a remnant. This was also supported by the well-differentiated uterine wall layers, which do not occur in congenital uterine anomalies. Notably, in patients with a history of trauma, it is important to consider the possibility of uterine rupture even in the absence of clinical signs.

Not applicable.

Conceptualization: D.H.K. Data curation: Y.E.K., S.H.N., and G.L.H. Formal analysis: G.L.H., and J.Y.J. Investigation: W.J.L., and C.H.M. Supervision: D.H.K. Writing - original draft: Y.E.K. Writing - review & editing: J.M.J., H.B.L., S.M.J., and D.H.K. All authors have read and agreed to the published version of the manuscript.

The authors have no conflicting interests.