Equine Gastrointestinal Lesions – NAVLE Study Guide

Overview and Clinical Importance

Colic is the leading cause of death in horses and represents the most common equine emergency presented to veterinarians. Understanding the distinction between strangulating and non-strangulating lesions is critical for the NAVLE, as it directly impacts treatment decisions, surgical urgency, and prognosis.

Strangulating lesions involve vascular compromise leading to ischemia and rapid tissue necrosis, requiring emergency surgical intervention. Non-strangulating lesions obstruct the intestinal lumen without immediate vascular compromise and may respond to medical management. The ability to differentiate these conditions clinically determines whether a horse survives.

Key Definitions and Classifications

Strangulating Obstruction

A strangulating obstruction involves both luminal obstruction AND vascular compromise. The blood supply to the intestinal wall is interrupted, leading to ischemia, mucosal barrier breakdown, bacterial translocation, endotoxemia, and rapid tissue death. These are surgical emergencies with a narrow window for intervention.

Non-Strangulating Obstruction

A non-strangulating obstruction blocks the intestinal lumen (simple obstruction) without immediate vascular compromise. Blood supply remains intact, allowing more time for diagnosis and potential medical management. However, prolonged distension can eventually compromise blood flow.

Classification of GI Lesions

Strangulating Lesions

Large Colon Volvulus (LCV)

Pathophysiology

Large colon volvulus occurs when the ventral and dorsal colons rotate on their long axis, typically greater than 360 degrees. The most common site is at the junction between the right ventral colon and cecum. Most rotations occur in a clockwise direction when viewed from behind the horse (dorsomedial volvulus). Rotation less than 270 degrees may cause obstruction without complete vascular compromise, while rotation greater than 360 degrees causes complete strangulation.

Predisposing Factors

• Postpartum mares: Increased abdominal space and pressure changes after foaling
• Large breed horses: Warmbloods, Thoroughbreds
• Dietary factors: Sudden feed changes, lush pasture
• Gas distension: Colonic tympany causing the colon to float

Clinical Signs

• Acute onset of severe, unrelenting abdominal pain
• Pain unresponsive or poorly responsive to analgesics
• Progressive abdominal distension (tympany)
• Rapid cardiovascular deterioration: tachycardia (greater than 60-80 bpm), prolonged CRT, congested mucous membranes
• In mares: vaginal mucosa color changes reflecting colonic compromise

Diagnostic Findings

Treatment

Emergency exploratory laparotomy via ventral midline celiotomy is required. Surgical steps include: needle decompression of gas, exteriorization of the colon, correction of the volvulus, and assessment of bowel viability. If the serosa is purple or black, euthanasia may be warranted. In cases of severe damage, large colon resection may be performed.

Prognosis

Prognosis depends on degree of volvulus and time to surgery. Torsions less than 270 degrees have a good prognosis. Strangulating torsions (greater than 360 degrees) or delayed surgery have a poor prognosis. Recurrence rate is 20-30% in horses without colopexy.

Strangulating Lipoma

Pathophysiology

A pedunculated lipoma is a benign fatty tumor suspended from the mesentery by a fibrovascular stalk (pedicle). The stalk can wrap around a segment of small intestine like a lasso, causing strangulation. The weight of the lipoma (greater than 33 grams is significant) and length of the pedicle determine strangulation potential. This is the most common cause of small intestinal strangulation in horses.

Risk Factors

• Age: Greater than 14-15 years (lipomas develop over time)
• Sex: Geldings at 2.3x higher risk than mares
• Breed: Ponies (OR 3.75), Arabians, Quarter Horses, Morgans
• Metabolic factors: Insulin resistance, obesity, PPID

Clinical Signs

• Acute onset of severe, unrelenting pain
• Nasogastric reflux (due to small intestinal obstruction)
• Elevated heart rate (often greater than 80 bpm)
• Rapid cardiovascular deterioration
• Distended small intestine on rectal palpation (bicycle tube feel)

Treatment and Prognosis

Treatment requires emergency surgery with transection of the pedicle and resection/anastomosis of devitalized intestine if needed. Short-term survival rate averages 43-48%; long-term survival 38%. Prognosis is better if surgery is performed early before cardiovascular compromise. Up to 50% of small intestine can be resected if necessary.

Memory Aid - LIPOMA Risk: Large pedicle, Insulin resistance, Ponies/older, Obese, Male (geldings), Aged (greater than 15 years)

Epiploic Foramen Entrapment (EFE)

Pathophysiology

The epiploic foramen (Winslow foramen) is a natural opening in the right dorsal abdomen bounded by the caudal vena cava (dorsally), portal vein (ventrally), liver (cranially), and pancreas (caudally). Small intestine (typically distal jejunum or ileum) can herniate through this opening, most commonly from left to right. Once entrapped, the intestine becomes edematous and cannot exit, leading to strangulation. EFE accounts for 2-8% of surgical colics.

Risk Factors

• Cribbing/windsucking: Strongest risk factor (changes in abdominal pressure)
• Age: Older horses (foramen enlarges as right liver lobe atrophies)
• Sex: More common in geldings
• Breed: Thoroughbreds

Clinical Signs and Diagnosis

• Acute onset severe pain, often unresponsive to analgesia
• Nasogastric reflux (may not provide pain relief)
• Rectal: Distended small intestine; pain response to traction on caudal cecal band
• Ultrasound: Distended, hypomotile small intestine in right dorsal quadrant
• Abdominocentesis: Serosanguineous fluid (may be misleading if fluid enters omental bursa)

Treatment and Prognosis

Surgical treatment requires careful reduction of entrapped intestine with EXTREME CAUTION - the portal vein is vulnerable to rupture, which causes fatal hemorrhage. The foramen cannot be manually dilated. Short-term survival is 70-79%. The ileum is involved in most cases, often requiring jejunocecostomy. Recurrence rate is low (EF often closes spontaneously after surgery in approximately 40% of cases).

Small Intestinal Volvulus

Small intestinal volvulus occurs when the intestine rotates greater than 180 degrees on its mesenteric axis. The ileum is typically the distal aspect due to its cecal attachment. Horses present with acute severe pain, rapid cardiovascular deterioration, gastric reflux, and distended small intestine on rectal examination. Emergency surgery is required with resection/anastomosis of devitalized bowel.

Intussusception

Intussusception is the invagination (telescoping) of one intestinal segment (intussusceptum) into an adjacent segment (intussuscipiens). Most common types are jejuno-jejunal, ileal-ileal, or ileocecal. Horses less than 3 years old are most commonly affected. Risk factors include parasitism (Anoplocephala perfoliata), enteritis, anthelmintic administration, and recent surgery.

Diagnostic Features

• Ultrasound: Characteristic 'bulls-eye' or 'target' appearance on cross-section
• Rectal: Sausage-shaped tubular structure; may feel turgid intussusception
• Clinical sign: Melena (digested blood) is a significant finding
• Abdominocentesis: May be normal (strangulated segment contained within intussuscipiens)

Treatment: Surgical reduction followed by resection and anastomosis. Manual reduction alone is not recommended due to high recurrence risk. Overall survival rate is approximately 53%. Prognosis worsens with longer affected segments.

Mesenteric Rent Entrapment

Mesenteric rents are defects (holes) in the small intestinal mesentery through which intestine can herniate and become incarcerated. Rents may be congenital or acquired (trauma, previous surgery). Clinical signs are identical to other strangulating lesions. Prognosis is generally poorer than other small intestinal lesions (less than 50% survival to discharge) due to hemorrhage from mesentery, difficulty in reduction, and length of intestine involved.

Non-Strangulating Lesions

Nephrosplenic Entrapment (Left Dorsal Displacement)

Pathophysiology

The left colon migrates dorsally between the spleen and body wall, becoming entrapped over the nephrosplenic ligament (connecting the left kidney to the spleen). The colon hangs like a dumbbell over the ligament. This is a non-strangulating obstruction - blood supply remains intact but luminal obstruction occurs. NSE accounts for 6-9% of colic cases.

Risk Factors

• Breed: Warmbloods, Arabians, deep-chested horses
• Age: Middle-aged horses
• Contributing factors: Gas accumulation, hypomotility, rolling

Clinical Signs and Diagnosis

• Mild to moderate intermittent colic
• Left-sided abdominal distension
• Normal to slightly elevated heart rate
• Rectal: Colon palpable in nephrosplenic space; unable to palpate left kidney or spleen in normal position
• Ultrasound: Gas shadowing at dorsal spleen obscuring kidney; spleen displaced ventrally (often past midline to right)

Treatment Options

Prognosis

Excellent prognosis - short-term survival approximately 94%. Recurrence rate is 3-21%. NSS ablation significantly decreases recurrence risk.

Impaction Colics

Pelvic Flexure Impaction

The most common type of large colon obstruction. The pelvic flexure is predisposed due to the 180-degree turn and dramatic decrease in luminal diameter. Risk factors include decreased water intake (winter months), dental disease, decreased exercise (stall rest), and coarse hay.

Clinical Signs

• Mild, intermittent colic
• Decreased fecal output, dry manure
• Decreased appetite
• Normal to slightly elevated heart rate
• Decreased gut sounds (present in 76%)
• Rectal: Large, doughy-to-firm mass in left ventral colon/pelvic flexure region

Treatment

• Medical management: IV fluids, oral fluids via nasogastric tube, mineral oil/laxatives, analgesics
• Surgery: Pelvic flexure enterotomy and lavage if unresponsive to medical treatment (3-5 days)

Prognosis: Excellent (greater than 95% survival with treatment)

Ileal Impaction

Most common small intestinal simple obstruction. Strongly associated with Coastal Bermuda hay feeding (southeastern US) and Anoplocephala perfoliata tapeworm infection. Clinical signs include moderate pain, nasogastric reflux, distended small intestine on rectal (may feel thickened ileal wall).

Treatment: Medical management with IV/oral fluids and lubricants. Surgery (ileocecal or jejunocecal anastomosis) required if unresponsive. Prognosis: Fair with surgical treatment.

Cecal Impaction

Located in right paralumbar fossa. Breed predisposition: Morgans, Arabians, Appaloosas. May be associated with A. perfoliata infection. Medical management success rate approximately 80%; surgical success 60-70%.

Right Dorsal Displacement

The pelvic flexure migrates between the cecum and body wall (lateral displacement) or around the cecum (medial displacement). May progress to 180-degree rotation. Clinical signs similar to nephrosplenic entrapment. Requires surgical correction - cannot be treated with phenylephrine/rolling.

Diagnostic Approach to Colic

Clinical Parameters Indicating Surgical Colic

Treatment Summary