Internal hernia (IH) is defined by the protrusion of abdominal organs through a peritoneal or mesenteric defects into a compartment within the abdominal cavity (1, 2). IH is a rare condition with a prevalence of less than 1% in the general population and is primarily reported in children as a congenital anomaly (3). In adults, it may develop as an acquired condition resulting from abdominal injury, peritoneal inflammation, or iatrogenic factors following previous surgical procedures (2, 4). As previously noted, IH can lead to intestinal obstruction in humans. When intestinal obstruction occurs, the affected intestinal segment undergoes strangulation, resulting in ischemia and posing a life-threatening risk (5, 6). Therefore, timely diagnosis is crucial; however, the identification of IH still remains a challenge in humans (4, 6). IH has not been previously reported in the field of veterinary medicine.

This report describes a rare cause of small intestinal obstruction associated with internal hernia in a cat. The present report describes congenital mesenteric defect for the first time in veterinary medicine.

Internal hernia (IH) is a rare condition in humans and remains unreported in dogs and cats. Its incidence is estimated to range from 0.2 to 0.9% in autopsy cases, contributing to 0.6–5.8% of all instances of small bowel obstruction (SBO) (4, 6). IH can lead to complications such as intestinal obstruction, strangulation, and subsequent necrosis affecting varying lengths of the intestine (4).

This case report describes a rare congenital defect in the small intestinal mesentery that resulted in SBO in a cat. The cat presented with acute digestive signs, and a physical examination identified an intra-abdominal mass-like lesion. Considering the cat’s age and medical history, the primary differentials included foreign body, intussusception, or other cause of obstruction.

The predominant reported etiologies of gastrointestinal obstruction in dogs and cats include foreign bodies, intussusception, neoplasia, abscess, granulomas, and the formation of strictures (7). Among the various etiology, ingestion of foreign bodies and intussusception was the most common cause of mechanical obstruction in cats (8). When intestinal obstruction occurs due to any cause, it results in reduced intestinal contents and inhibited intestinal motility. Furthermore, direct distension of the intestinal wall by foreign object can induce venous congestion and edema, potentially leading to more severe vascular damage and necrosis (9). For a favorable prognosis, prompt diagnosis and therapeutic intervention was essential.

In this case, both radiographic and ultrasound examinations was used for diagnosis. Although abdominal radiography suggested the potential for intestinal obstruction, but identifying the exact cause was not possible. Subsequent ultrasound examination raised suspicion of intestinal intussusception. As a result, a surgical approach was conducted in this cat, leading to the ultimate diagnosis of intestinal obstruction due to IH.

Internal hernias are classified based on the location of the defect openings, with Meyers categorizing them into paraduodenal, pericecal, foramen of Winslow, transmesenteric, transmesocolic, intersigmoid, and retroanastomotic types (10). Among these, transmesenteric herniation caused by a congenital anomaly is the most common type and eight congenital cases were first reported in 1836 (11). The pathophysiology of mesenteric defects remains unclear, with various hypotheses proposed, including partial regression of the dorsal mesentery, developmental enlargement of a poorly vascularized areas, rapid elongation of a mesenteric segment, and compression of the mesentery by the colon during the in prenatal period (4, 12). Congenital mesenteric defects are frequently associated with other gastrointestinal anomalies, particularly small bowel atresia (13).

With recent advancements in diagnostic imaging technology, the characterization of different types of IH using CT has been on the rise (4). However, preoperative diagnosis of mesenteric defect still remains challenging for both clinicians and radiologist (6).

In this report, limitations arose as additional CT scans could not be conducted. However, a rapid diagnostic approach and exploratory laparotomy successfully averted further complications. The segment of bowel affected by obstruction in this cat was relatively short, particularly when compared to the extensive mesenteric defect site. Additionally, the duration of ischemia was not prolonged, resulting in minimal intestinal damage and a quick recovery. Histopathological examination of the mesentery was not conducted in this case, although it could have provided valuable insights into the congenital etiology of the condition and the nature of tissue changes. Generally, diagnoses are typically made through emergency exploratory laparotomy, and histopathological information is rarely available even in human cases. Transmesenteric hernia is a rare cause contributing to small bowel obstruction. In the case of bowel obstruction in relatively young animals, it is advisable to consider congenital mesenteric defect as a potential differential diagnosis.

In conclusion, to the best of our knowledge, this case report represents the first documentation of a small intestinal mesenteric defect in a cat. The consideration of a congenital mesenteric defect should be included in the differential diagnosis for relatively young dogs and cats displaying signs of SBO, particularly in the absence of external hernia, suspicion of a foreign body, prior abdominal surgery, or trauma.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethical approval was not required for the studies involving animals in accordance with the local legislation and institutional requirements because This paper is a case report based on client-owned animals, and consent was obtained from the owner of the cat for the publication of this case report and any accompanying images. Written informed consent was obtained from the owners for the participation of their animals in this study.

M-HK: Conceptualization, Writing – original draft, Writing – review & editing. Y-CK: Data curation, Writing – original draft, Writing – review & editing. J-WY: Data curation, Writing – original draft, Writing – review & editing. H-MP: Supervision, Writing – original draft, Writing – review & editing.