Small Intestinal Strangulation and Hernias (Lipoma, Hernias)

Small intestinal strangulation and hernias represent a critical category of equine acute abdominal disease characterized by mechanical obstruction of the intestinal lumen and compromise of vascular supply to a segment of the small intestine, leading to ischemia, necrosis, and rapid systemic deterioration. This condition encompasses various etiologies, including pedunculated lipomas, internal hernias (e.g., epiploic foramen entrapment, mesenteric defects), and external hernias (e.g., inguinal, scrotal, umbilical, diaphragmatic). The disease is a leading cause of severe colic in horses, particularly in older animals, and requires prompt surgical intervention to prevent fatal outcomes. In the equine industry, this condition is of paramount importance due to its high morbidity and mortality, affecting performance horses across disciplines such as Thoroughbred racing, Standardbred racing, dressage, eventing, and pleasure riding. The economic impact includes loss of athletic career, prolonged hospitalization, and high treatment costs. Early recognition and referral to a surgical facility are critical for successful management.

The primary etiologies of small intestinal strangulation and hernias in horses include: (1) Pedunculated lipomas, which are benign adipose tumors arising from the mesentery, commonly found in older horses (typically >15 years), that can wrap around a segment of small intestine, causing strangulation. (2) Internal hernias, such as entrapment of the small intestine through the epiploic foramen (a natural opening between the portal vein and the caudate liver lobe), through mesenteric defects (congenital or acquired), or through the gastrosplenic ligament. (3) External hernias, including inguinal/scrotal hernias (more common in stallions, often associated with breeding or trauma), umbilical hernias (congenital or acquired), and diaphragmatic hernias (traumatic or congenital). (4) Volvulus or torsion of the small intestine, which can occur spontaneously or secondary to other lesions. (5) Intussusception, where a segment of intestine telescopes into an adjacent segment, often associated with altered motility or masses. (6) Adhesions from previous abdominal surgery, which can create internal hernias or cause strangulation. (7) Foreign body ingestion or impaction, though less common. The underlying mechanism involves mechanical obstruction and vascular compromise, leading to ischemia, reperfusion injury upon surgical correction, and systemic inflammatory response syndrome (SIRS).

Small intestinal strangulation and hernias are significant causes of colic in horses, accounting for approximately 10-20% of all surgical colic cases. Pedunculated lipomas are most prevalent in older horses, particularly ponies and breeds such as Arabians and Quarter Horses, with a mean age of 15-20 years. Internal hernias, especially epiploic foramen entrapment, are more common in middle-aged horses (5-15 years) and are overrepresented in Thoroughbreds and Warmbloods, possibly due to breed-specific anatomical variations. Inguinal/scrotal hernias occur predominantly in stallions, with a higher incidence in Standardbreds and Tennessee Walking Horses, and are often associated with breeding activity or trauma. There is no significant sex predisposition for other types of hernias. Management factors such as stall confinement, high concentrate diets, and lack of regular exercise may increase the risk of colic. Seasonal variations have been reported, with some studies showing a higher incidence in spring and fall. Mortality rates are high, ranging from 30-70% depending on the duration of strangulation, extent of intestinal damage, and promptness of surgical intervention. Affected horses often have a poor prognosis for return to athletic function, especially if extensive resection is required.

The pathophysiology of small intestinal strangulation involves a cascade of events initiated by mechanical obstruction and vascular occlusion. The strangulating lesion compromises both arterial inflow and venous outflow, leading to venous congestion, edema, and progressive ischemia. Within minutes, the intestinal mucosa becomes hypoxic, leading to disruption of the mucosal barrier, increased permeability, and translocation of bacteria and endotoxins into the peritoneal cavity and systemic circulation. This triggers a severe inflammatory response, with release of pro-inflammatory cytokines (TNF-α, IL-1, IL-6), activation of neutrophils, and production of reactive oxygen species. Reperfusion injury occurs when blood flow is restored during surgery, exacerbating tissue damage through oxidative stress and leukocyte infiltration. The ischemic segment becomes necrotic, leading to loss of mucosal integrity, hemorrhage, and eventually perforation if not resected. Systemically, the horse develops hypovolemia due to fluid sequestration into the intestinal lumen and peritoneal cavity, electrolyte imbalances, acid-base disturbances, and endotoxemia, which can progress to septic shock, disseminated intravascular coagulation (DIC), and multiple organ dysfunction syndrome (MODS). The severity of these changes correlates with the duration and degree of strangulation.

Intrinsic predisposing factors include age (older horses for lipomas, middle-aged for epiploic foramen entrapment), breed (Thoroughbreds and Warmbloods for internal hernias, Standardbreds for inguinal hernias), sex (stallions for inguinal/scrotal hernias), and individual anatomical variations such as a large epiploic foramen or long mesentery. Extrinsic factors include sudden changes in management, such as abrupt stall confinement, which reduces intestinal motility and increases gas accumulation, potentially predisposing to displacement or herniation. High concentrate diets with low forage intake can alter gut motility and increase intraluminal pressure. Transportation stress, intense exercise, and trauma can precipitate herniation, particularly inguinal hernias. Previous abdominal surgery increases the risk of adhesions and internal hernias. Additionally, obesity and hyperlipemia may be associated with lipoma formation. In broodmares, pregnancy and parturition can increase intra-abdominal pressure, potentially contributing to diaphragmatic hernias.

Clinical signs of small intestinal strangulation and hernias are typically acute and severe, reflecting the rapid onset of ischemia. Horses exhibit moderate to severe colic, characterized by pawing, flank watching, rolling, lying down, and getting up frequently. They may be reluctant to move and show signs of abdominal distension. Heart rate is elevated, often exceeding 60-80 beats per minute, and mucous membranes may be injected or toxic with prolonged capillary refill time (>3 seconds). Nasogastric intubation often yields large volumes of reflux (>2 liters) due to gastric accumulation of fluid and gas. Rectal palpation may reveal distended small intestinal loops, a tight band or mass (e.g., lipoma), or an empty caudal abdomen in cases of cranial displacement. Abdominocentesis yields peritoneal fluid that may be serosanguinous or bloody, with elevated protein and lactate levels. In cases of inguinal hernia, there may be a palpable swelling in the scrotal or inguinal region, and the horse may show signs of stranguria. Systemic signs include dehydration, tachypnea, and signs of endotoxemia such as injected mucous membranes and increased capillary refill time. Without intervention, the horse progresses to shock, cardiovascular collapse, and death.

Differential diagnoses for small intestinal strangulation and hernias include: (1) Large colon volvulus or torsion, which typically presents with severe abdominal distension and rapid deterioration; rectal palpation reveals distended large colon, and peritoneal fluid may be hemorrhagic. (2) Anterior enteritis (duodenitis-proximal jejunitis), characterized by gastric reflux, but often less severe pain and absence of strangulating lesion; ultrasound may show thickened duodenum. (3) Ileal impaction, which presents with mild to moderate colic and nasogastric reflux; rectal palpation reveals a firm mass in the right caudal abdomen. (4) Nephrosplenic entrapment (left dorsal displacement of the large colon), which can cause moderate colic; rectal palpation and ultrasound may reveal the colon between the spleen and kidney. (5) Intussusception, which may present with acute colic and palpable mass on rectal exam; ultrasound may show a target-like lesion. (6) Peritonitis, which can cause colic and fever; peritoneal fluid analysis shows elevated WBC and protein. (7) Gastric dilatation or rupture, which may present with severe colic and reflux; rupture leads to shock and death. (8) Mesenteric thrombosis, often due to Strongylus vulgaris larvae, causing acute colic and hemorrhagic peritoneal fluid. (9) Strangulating lipoma of the large colon, which can mimic small intestinal strangulation but is less common. (10) Diaphragmatic hernia, which may present with respiratory distress and colic; thoracic auscultation may reveal intestinal sounds. Definitive diagnosis often requires exploratory laparotomy.

The diagnostic algorithm for suspected small intestinal strangulation and hernias begins with a thorough physical examination, including assessment of pain severity, heart rate, respiratory rate, mucous membrane color, capillary refill time, and abdominal auscultation. Nasogastric intubation is performed to check for reflux; a volume >2 liters is significant. Rectal palpation is essential to assess for distended small intestine, masses, or hernial rings. Abdominocentesis is performed to obtain peritoneal fluid for analysis; elevated protein (>3.5 g/dL) and lactate (>2 mmol/L) or the presence of blood suggests strangulation. Abdominal ultrasonography is a valuable non-invasive tool to evaluate small intestinal wall thickness (>3 mm is abnormal), diameter (>3 cm suggests distension), and motility (decreased or absent). If the horse is stable, further imaging such as radiography may be used, but it is less sensitive for small intestinal lesions. In cases of suspected inguinal hernia, scrotal ultrasound can confirm the presence of intestine. If the horse is a candidate for surgery, exploratory laparotomy is both diagnostic and therapeutic. The decision to proceed to surgery is based on the severity of pain, cardiovascular status, and the presence of abnormal peritoneal fluid. A stepwise approach ensures timely intervention.

Laboratory findings in small intestinal strangulation and hernias reflect dehydration, electrolyte imbalances, acid-base disturbances, and systemic inflammation. Complete blood count (CBC) may show hemoconcentration (elevated PCV and total protein), leukopenia or leukocytosis, and thrombocytopenia in severe cases. Serum biochemistry may reveal elevated creatinine and urea due to prerenal azotemia, hypochloremia, hypokalemia, and metabolic acidosis (decreased bicarbonate, increased lactate). Plasma lactate is a key prognostic indicator; levels >5 mmol/L are associated with a poor prognosis. Peritoneal fluid analysis is critical: normal fluid is clear and straw-colored with WBC <5000/μL and total protein <2.5 g/dL. In strangulation, the fluid becomes serosanguinous or hemorrhagic, with elevated WBC (>10,000/μL), total protein (>3.5 g/dL), and lactate (>2 mmol/L). The peritoneal fluid lactate-to-plasma lactate ratio >1 is suggestive of intestinal ischemia. Serum amyloid A (SAA) is an acute-phase protein that may be elevated, but it is not specific. In horses with endotoxemia, blood gas analysis may show metabolic acidosis with compensatory respiratory alkalosis. Additionally, measurement of serum electrolytes and ionized calcium is important for fluid therapy planning.

Abdominal ultrasonography is the most useful imaging modality for small intestinal strangulation and hernias. Findings include distended small intestinal loops with a diameter >3 cm, thickened walls (>3 mm), and reduced or absent motility. The presence of free peritoneal fluid with echogenic particles suggests peritonitis or hemorrhage. In cases of epiploic foramen entrapment, the distended loops may be seen in the right cranial abdomen. For inguinal hernias, scrotal ultrasound can identify intestinal loops within the scrotum. Radiography is of limited value in adult horses due to the size of the abdomen, but in foals, it may show distended loops. Computed tomography (CT) is rarely used in adult horses due to size constraints, but it can be helpful in foals or for specific cases. Magnetic resonance imaging (MRI) is not practical for abdominal imaging in horses. Scintigraphy is not commonly used for colic. In surgical cases, intraoperative findings are definitive. Endoscopy is not useful for small intestinal evaluation. Therefore, ultrasonography is the primary imaging tool, and it should be performed by experienced personnel to guide surgical decision-making.

Cytological examination of peritoneal fluid is essential in diagnosing strangulating lesions. In early stages, the fluid may be serosanguinous with increased red blood cells and neutrophils. As ischemia progresses, the fluid becomes more hemorrhagic, and degenerative neutrophils and bacteria may be seen, indicating septic peritonitis. Histopathology of resected intestinal segments reveals characteristic changes: mucosal necrosis, hemorrhage, edema, and infiltration of neutrophils. The severity of mucosal damage correlates with the duration of strangulation. In chronic cases, fibrosis and adhesions may be present. Histopathology of a pedunculated lipoma shows mature adipose tissue with a fibrous stalk. In cases of hernias, the hernial sac may show inflammation and fibrosis. These findings are important for confirming the diagnosis and assessing the extent of damage, which influences the prognosis and the need for extensive resection.

Treatment of small intestinal strangulation and hernias requires aggressive medical stabilization followed by surgical intervention. Initial therapy includes intravenous fluid resuscitation with polyionic isotonic fluids (e.g., lactated Ringer's solution) at a rate of 10-20 mL/kg/hour to correct hypovolemia and electrolyte imbalances. Hypertonic saline (7.5% NaCl, 4-6 mL/kg IV) may be used for rapid expansion of plasma volume, followed by isotonic fluids. Analgesia is provided with non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine (1.1 mg/kg IV) or phenylbutazone (4.4 mg/kg IV), and alpha-2 agonists like detomidine (0.01-0.02 mg/kg IV) or xylazine (0.5-1.1 mg/kg IV) for sedation and pain control. In severe cases, lidocaine continuous rate infusion (CRI) at 1.3 mg/kg IV bolus followed by 0.05 mg/kg/min may be used for analgesia and prokinetic effects. Antibiotics are indicated if peritonitis is suspected; a combination of penicillin G (22,000 IU/kg IV q6h) and gentamicin (6.6 mg/kg IV q24h) is commonly used. Surgical treatment involves exploratory celiotomy, identification of the strangulating lesion, and correction. This may include reduction of the hernia, resection and anastomosis of necrotic intestine, or removal of a lipoma. Postoperative care includes continued fluid therapy, nasogastric decompression, and monitoring for complications such as ileus, peritonitis, and laminitis. In cases of inguinal hernia, surgical reduction and orchiectomy may be necessary.

The prognosis for small intestinal strangulation and hernias is guarded to poor, depending on several factors. Short-term survival rates for horses undergoing surgery range from 50-80%, but long-term survival to discharge is lower, around 40-60%. Negative prognostic indicators include: duration of colic >24 hours, heart rate >80 bpm, plasma lactate >5 mmol/L, peritoneal fluid lactate >2 mmol/L, and the need for extensive intestinal resection (>3 meters). The presence of septic peritonitis or endotoxemia also worsens the prognosis. Return to athletic function is possible in some cases, but many horses have reduced performance due to adhesions, chronic colic, or laminitis. Recurrence of strangulation is possible, especially if the underlying cause (e.g., lipoma) is not completely removed. Owners should be counseled about the high risk of complications and the potential for euthanasia during or after surgery.

Postoperative follow-up is crucial for monitoring recovery and detecting complications. Horses should be hospitalized for at least 5-7 days after surgery. Nasogastric reflux should be monitored every 2-4 hours; a decrease in reflux volume indicates resolution of ileus. Serial physical examinations, including heart rate, mucous membranes, and abdominal auscultation, should be performed. Blood work, including lactate and electrolytes, should be repeated daily. Abdominal ultrasonography may be used to assess intestinal motility and detect adhesions. Once discharged, the horse should have a gradual return to exercise over 4-6 weeks, starting with hand-walking and progressing to light work. Dietary management includes small, frequent meals of high-quality forage and a low-starch concentrate. Recheck examinations are recommended at 2 weeks, 6 weeks, and 3 months post-surgery. Long-term monitoring for signs of colic or laminitis is essential. Farriery care should be maintained to prevent laminitis, especially if the horse was in a high-risk category.

Clinical pearls: (1) Always perform nasogastric intubation in any colic case; a large reflux volume is a red flag for small intestinal obstruction. (2) Peritoneal fluid lactate >2 mmol/L is a strong indicator of strangulation and warrants immediate surgical referral. (3) In older horses with acute colic, always consider pedunculated lipoma as a cause. (4) In stallions with colic, always palpate the scrotum for inguinal hernia. (5) Early surgical intervention improves survival; do not delay referral. Pitfalls: (1) Administering flunixin meglumine can mask pain and delay surgical decision-making; use judiciously. (2) Failure to recognize the severity of the condition and delaying surgery can lead to irreversible intestinal necrosis and death. (3) Overlooking the possibility of a diaphragmatic hernia in horses with respiratory distress. (4) Inadequate fluid resuscitation before surgery can lead to cardiovascular collapse. (5) Not monitoring for laminitis postoperatively, which is a common and devastating complication.

Current drug protocols for small intestinal strangulation and hernias are based on Plumb's Veterinary Drug Handbook and ACVIM guidelines. Fluid therapy: Lactated Ringer's solution IV at 10-20 mL/kg/hour for initial resuscitation, then adjusted based on hydration status. Hypertonic saline (7.5% NaCl) at 4-6 mL/kg IV over 10-15 minutes for rapid expansion. Analgesics: Flunixin meglumine 1.1 mg/kg IV q12h for up to 3 days; Phenylbutazone 4.4 mg/kg IV q24h; Detomidine 0.01-0.02 mg/kg IV q4-6h as needed; Xylazine 0.5-1.1 mg/kg IV q4-6h; Morphine 0.1-0.2 mg/kg IM or IV q4-6h (use with caution). Lidocaine CRI: 1.3 mg/kg IV bolus over 5 minutes, then 0.05 mg/kg/min IV. Antibiotics: Penicillin G potassium 22,000 IU/kg IV q6h; Gentamicin 6.6 mg/kg IV q24h; Metronidazole 15 mg/kg PO q6h if anaerobic infection suspected. Anti-endotoxemic therapy: Polymyxin B 1000-6000 IU/kg IV q8-12h in severe endotoxemia. Gastroprotectants: Omeprazole 4 mg/kg PO q24h; Sucralfate 20 mg/kg PO q6-8h. Prokinetics: Lidocaine CRI as above; Metoclopramide 0.04 mg/kg/h CRI (use with caution). All dosages should be adjusted based on renal function and clinical response.

Landmark studies and consensus guidelines have shaped the management of small intestinal strangulation and hernias. A prospective study by Mair and Smith (2005) reported a survival rate of 68% for horses undergoing surgery for small intestinal strangulation, with factors such as heart rate and peritoneal fluid lactate being significant predictors. Another study by Proudman et al. (2002) found that horses with pedunculated lipomas had a higher mortality rate compared to other causes. The ACVIM consensus statement on colic (2014) emphasizes the importance of early referral and aggressive fluid therapy. Research by van der Linden et al. (2003) demonstrated that peritoneal fluid lactate >2 mmol/L is a sensitive indicator of strangulation. A meta-analysis by Curtis et al. (2015) confirmed that plasma lactate >5 mmol/L is associated with a poor prognosis. Surgical techniques, such as resection and anastomosis, have been refined, with studies showing that the use of stapled anastomosis reduces surgery time and complications. Postoperative ileus remains a major challenge, and lidocaine CRI has been shown to reduce its incidence (Malone et al., 2006). Overall, the evidence supports prompt surgical intervention, aggressive cardiovascular support, and careful postoperative monitoring to improve outcomes.