Intestinal Intussusception

Intestinal intussusception is a surgical condition characterized by the telescoping or invagination of one segment of the gastrointestinal tract (the intussusceptum) into the lumen of an adjacent segment (the intussuscipiens). This invagination leads to obstruction of the intestinal lumen, vascular compromise of the intussusceptum, and subsequent ischemia, necrosis, and potentially perforation if left untreated. The condition can occur at any level of the gastrointestinal tract, from the stomach to the rectum, but is most commonly encountered at the ileocecocolic junction in dogs and cats. Intussusception is classified based on the direction of the invagination (anterograde, retrograde), the anatomical location (e.g., enteric, cecocolic, colocolic), and the underlying cause (idiopathic, secondary to enteritis, foreign body, neoplasia, or previous surgery). The severity of the disease ranges from transient, spontaneously reducing intussusceptions to irreducible, strangulating lesions that require surgical intervention. Intussusception is a true surgical emergency, as delayed intervention can lead to irreversible intestinal ischemia, septic peritonitis, and death.

The etiology of intestinal intussusception is multifactorial, with any condition that alters normal intestinal motility or creates a focal intraluminal or mural lesion predisposing to invagination. In young animals, the most common cause is parasitic or viral enteritis, particularly canine parvovirus, which causes hypermotility and inflammation of the intestinal wall. In older animals, intussusception is often secondary to space-occupying lesions such as intestinal neoplasia (e.g., adenocarcinoma, lymphoma, leiomyoma), foreign bodies, or previous intestinal surgery (e.g., enterotomy or resection and anastomosis) that creates a nidus for invagination. Other predisposing factors include intraluminal parasites (e.g., roundworms, hookworms), dietary indiscretion, and conditions that cause mural thickening or altered peristalsis, such as inflammatory bowel disease. Iatrogenic causes include rough handling of the intestines during abdominal surgery, which can initiate an intussusception. The exact biomechanical trigger is thought to involve a disparity in motility between adjacent intestinal segments, where a hypermotile segment invaginates into a hypomotile or dilated segment. Anatomically, the ileocecocolic region is particularly vulnerable due to the abrupt change in luminal diameter and the presence of the ileocecal valve, which may act as a lead point. Cellular mechanisms involve the release of inflammatory mediators, such as cytokines and prostaglandins, which further disrupt normal peristaltic coordination.

Intestinal intussusception is a relatively common surgical emergency in small animal practice, accounting for approximately 0.5% to 1% of all surgical admissions in dogs and cats. It can occur at any age, but there is a bimodal distribution: a peak in young animals (less than 1 year of age) and a second peak in older animals (greater than 7 years of age). In young animals, the condition is often associated with infectious enteritis, particularly canine parvovirus, and is more common in puppies and kittens. In older animals, intussusception is frequently secondary to intestinal neoplasia. There is no strong breed predisposition, but certain breeds may be overrepresented due to their susceptibility to underlying conditions. For example, breeds prone to parvovirus (e.g., Rottweilers, Doberman Pinschers, Pit Bulls) may have a higher incidence of intussusception. In cats, intussusception is less common than in dogs but can occur secondary to enteritis, foreign bodies, or neoplasia. No significant sex predilection has been reported. The condition is more common in animals with a history of gastrointestinal disease, recent abdominal surgery, or those receiving medications that alter intestinal motility (e.g., opioids).

The pathophysiology of intestinal intussusception involves a cascade of events that begin with the invagination of a segment of intestine into the distal lumen. The intussusceptum is carried along by peristalsis, and as it advances, it pulls the mesentery with it, leading to compression of the mesenteric vessels. This vascular compromise initially causes venous congestion, leading to edema and thickening of the intestinal wall. As the venous pressure increases, arterial blood flow becomes impaired, resulting in ischemia of the intussusceptum. The ischemic tissue becomes increasingly friable and necrotic, and if the intussusception is not reduced, the affected segment may become gangrenous and perforate, leading to septic peritonitis. The intussuscipiens, or the outer segment, also becomes distended and edematous, further compromising the blood supply. The obstruction of the intestinal lumen leads to accumulation of gas and fluid proximal to the intussusception, causing abdominal distension, vomiting, and dehydration. The systemic inflammatory response to ischemia and necrosis can lead to endotoxemia and sepsis, as the intestinal barrier becomes compromised, allowing translocation of bacteria and toxins into the peritoneal cavity and bloodstream. The severity of the disease depends on the duration of the intussusception, the degree of vascular compromise, and the presence of concurrent conditions. In some cases, the intussusception may spontaneously reduce, but this is unpredictable and should not be relied upon.

Predisposing factors for intestinal intussusception can be categorized into intrinsic and extrinsic factors. Intrinsic factors include age (young animals are more susceptible due to immature intestinal motility and immune system), breed (certain breeds may have a genetic predisposition to conditions that lead to intussusception, such as parvovirus), and underlying gastrointestinal diseases (e.g., inflammatory bowel disease, parasitic infections, neoplasia). Anatomical factors, such as the presence of a lead point (e.g., a polyp, tumor, or foreign body), can also predispose to intussusception. Extrinsic factors include dietary indiscretion, which can cause hypermotility, and previous abdominal surgery, which may create adhesions or alter motility. Management factors, such as the use of medications that affect intestinal motility (e.g., opioids, anticholinergics), can also increase the risk. In addition, stress and environmental changes may contribute to the development of intussusception in susceptible animals. It is important to note that in many cases, no specific predisposing factor is identified, and the intussusception is considered idiopathic.

The clinical signs of intestinal intussusception vary depending on the location, duration, and degree of obstruction. In the acute phase, animals typically present with a history of vomiting, anorexia, and lethargy. Abdominal pain is common, and palpation may reveal a tubular or sausage-shaped mass in the abdomen, particularly in the cranial or mid-abdominal region. The mass may be firm and tender. Animals may also exhibit diarrhea, which can be bloody or mucoid, and tenesmus if the intussusception is located in the colon or rectum. As the condition progresses, signs of shock, such as pale mucous membranes, tachycardia, weak pulses, and hypothermia, may develop due to dehydration and sepsis. In chronic cases, the clinical signs may be more subtle, with intermittent vomiting, weight loss, and a palpable abdominal mass. The severity of clinical signs is often correlated with the degree of vascular compromise and the presence of peritonitis. In some cases, the intussusception may be intermittent, with periods of apparent recovery followed by recurrence of signs. Physical examination findings may include dehydration, abdominal distension, and a palpable mass. In cases of perforation, signs of septic peritonitis, such as fever, abdominal rigidity, and severe pain, may be present.

The differential diagnoses for intestinal intussusception include other causes of intestinal obstruction, such as foreign bodies, neoplasia, volvulus, and intraluminal masses. Additionally, conditions that cause vomiting and diarrhea, such as gastroenteritis, pancreatitis, and peritonitis, should be considered. Specific differentials include: 1) Intestinal foreign body: Often presents with acute vomiting and abdominal pain; radiographs may show a radiopaque foreign body or gas patterns suggestive of obstruction; ultrasound may reveal a hyperechoic intraluminal mass. 2) Intestinal neoplasia: More common in older animals; may present with chronic weight loss, vomiting, and a palpable abdominal mass; imaging may show a mural mass or thickening; biopsy is definitive. 3) Intestinal volvulus: A surgical emergency with rapid onset of severe abdominal pain, distension, and shock; radiographs may show a 'whirlpool' sign on ultrasound; requires immediate surgery. 4) Gastroenteritis: Usually less severe, with vomiting and diarrhea but no palpable mass; imaging is unremarkable; responds to medical management. 5) Pancreatitis: Presents with vomiting, abdominal pain, and sometimes diarrhea; laboratory findings include elevated lipase and amylase; imaging may show pancreatic changes. 6) Peritonitis: Can be primary or secondary; presents with fever, abdominal pain, and effusion; imaging may show free fluid; abdominocentesis is diagnostic. 7) Intestinal adhesions or strictures: May cause chronic obstruction; history of previous surgery; imaging may show a narrowed segment. 8) Ileus: Functional obstruction due to inflammation, electrolyte imbalances, or postoperative; imaging shows generalized gas distension without a mechanical obstruction. 9) Intestinal parasitism: Especially in young animals; may cause diarrhea and weight loss; fecal examination is diagnostic. 10) Inflammatory bowel disease: Chronic vomiting and diarrhea; imaging may show thickened intestinal walls; biopsy is needed for definitive diagnosis.

The diagnostic algorithm for intestinal intussusception begins with a thorough history and physical examination. If an intussusception is suspected, the following steps are recommended: 1) Baseline blood work (complete blood count, serum biochemistry, and electrolytes) to assess hydration status, organ function, and the presence of inflammation or infection. 2) Abdominal radiographs: Survey radiographs may show a soft tissue mass, loss of serosal detail, or signs of intestinal obstruction (e.g., dilated loops of bowel, gas patterns). However, radiographs are not definitive for intussusception. 3) Abdominal ultrasound: This is the imaging modality of choice for confirming intussusception. Ultrasound typically shows a characteristic 'target' or 'bull's-eye' lesion in transverse section, and a 'pseudokidney' or 'sandwich' appearance in longitudinal section. Ultrasound can also assess the viability of the intussusceptum, the presence of free fluid, and the underlying cause (e.g., foreign body, neoplasia). 4) If ultrasound is inconclusive or if the patient is unstable, a computed tomography (CT) scan may be performed. CT can provide detailed images of the intussusception and any lead point, and is particularly useful in chronic cases. 5) In some cases, exploratory laparotomy is both diagnostic and therapeutic. If the patient is unstable or if imaging is not available, surgery may be performed based on clinical suspicion. 6) During surgery, the intussusception is identified and manually reduced if possible. If the intestine is non-viable, a resection and anastomosis is performed. 7) Postoperative care includes monitoring for recurrence, which is more common in young animals. The diagnostic algorithm should be tailored to the individual patient, taking into account the stability of the patient and the availability of diagnostic tools.

Laboratory findings in intestinal intussusception are non-specific but can support the diagnosis and assess the severity of the condition. A complete blood count may show hemoconcentration (elevated packed cell volume) due to dehydration, leukocytosis with a left shift due to inflammation or infection, and thrombocytopenia in cases of sepsis. Serum biochemistry may reveal electrolyte imbalances (e.g., hypokalemia, hyponatremia) due to vomiting, elevated liver enzymes (e.g., ALT, ALP) due to decreased hepatic perfusion, and elevated renal parameters (BUN, creatinine) due to prerenal azotemia. Blood gas analysis may show metabolic alkalosis due to vomiting, or metabolic acidosis in cases of sepsis. Inflammatory biomarkers, such as C-reactive protein (CRP) and serum amyloid A (SAA), may be elevated. Coagulation panel (PT/aPTT) may be prolonged in cases of disseminated intravascular coagulation (DIC). Synovial fluid analysis is not relevant for this condition. Urinalysis may show concentrated urine due to dehydration, or casts and proteinuria in cases of renal compromise. In cases of septic peritonitis, abdominocentesis may yield fluid with intracellular bacteria, degenerate neutrophils, and high protein content. These laboratory findings are not diagnostic for intussusception but are important for preoperative stabilization and postoperative management.

Imaging plays a crucial role in the diagnosis of intestinal intussusception. Abdominal radiographs are often the first imaging modality performed. In the early stages, radiographs may be unremarkable or show a soft tissue mass in the mid-abdomen. As the obstruction progresses, dilated loops of small intestine with gas and fluid may be seen proximal to the intussusception, and a loss of serosal detail may indicate peritonitis. However, radiographs are not sensitive or specific for intussusception. Abdominal ultrasound is the imaging modality of choice. In transverse section, an intussusception appears as a 'target' or 'bull's-eye' lesion, with concentric rings of hyperechoic and hypoechoic tissue. In longitudinal section, it appears as a 'pseudokidney' or 'sandwich' sign, with alternating hyperechoic and hypoechoic layers. Ultrasound can also assess the viability of the intussusceptum by evaluating blood flow with Doppler, and can identify the presence of free fluid or a lead point. Computed tomography (CT) is increasingly used, especially in chronic or complex cases. CT provides detailed cross-sectional images and can help identify the exact location of the intussusception, the presence of a lead point (e.g., neoplasia), and the degree of vascular compromise. CT is also useful for surgical planning. Magnetic resonance imaging (MRI) is rarely used for this condition but may be helpful in cases of suspected neoplasia. Fluoroscopy with contrast enema can be used to diagnose and sometimes reduce intussusception, but this is less commonly performed in veterinary medicine. In all cases, imaging findings must be correlated with clinical signs and laboratory results.

Cytology and histopathology are important in the diagnosis and management of intestinal intussusception, particularly when an underlying cause is suspected. During surgery, if a mass or abnormal tissue is identified, fine-needle aspiration (FNA) or biopsy may be performed. Cytology of FNA samples from an intussusception may show inflammatory cells, necrotic debris, or neoplastic cells if a tumor is present. Histopathology of resected intestinal segments is essential to confirm the diagnosis and to identify the underlying cause. In cases of intussusception secondary to enteritis, histopathology may show mucosal inflammation, ulceration, and necrosis. In cases of neoplasia, histopathology will reveal the tumor type, grade, and surgical margins. For example, intestinal adenocarcinoma may show infiltrative glands with desmoplasia, while lymphoma may show a monomorphic population of lymphocytes. Histopathology is also important to assess the viability of the intestinal margins and to ensure complete resection of any neoplastic tissue. In cases of chronic intussusception, fibrosis and adhesions may be present. Special stains, such as immunohistochemistry, may be used to differentiate tumor types. The results of histopathology guide further treatment and prognosis.

The treatment of intestinal intussusception is primarily surgical. Preoperative stabilization is crucial and includes intravenous fluid therapy to correct dehydration and electrolyte imbalances, and administration of broad-spectrum antibiotics if sepsis is suspected. The surgical approach is a midline celiotomy. The entire gastrointestinal tract should be examined to identify the intussusception and any other lesions. The intussusception is gently manipulated to reduce it, using traction and counter-traction. If the intussusception is irreducible or if the intestine is non-viable (e.g., dark, thin, or perforated), a resection and anastomosis is performed. The affected segment is resected, and the healthy ends are anastomosed using a simple interrupted or continuous pattern with absorbable monofilament suture (e.g., polydioxanone, 3-0 or 4-0). In cases of cecocolic intussusception, a typhlectomy may be performed. After reduction or resection, the abdomen is lavaged with warm sterile saline, and the abdomen is closed routinely. Postoperative management includes continued fluid therapy, pain management, and nutritional support. Early enteral nutrition is recommended to promote intestinal healing and reduce the risk of recurrence. In cases of recurrent intussusception, a technique called enteroplication may be performed, where the intestinal loops are sutured together to prevent re-invagination. However, this is controversial and is reserved for cases with a high risk of recurrence. The choice of surgical technique depends on the viability of the intestine and the underlying cause. In all cases, the underlying cause (e.g., foreign body, neoplasia) should be addressed to prevent recurrence.

The prognosis for intestinal intussusception is generally good if treated early and if there is no underlying malignancy. The short-term prognosis is excellent for animals that undergo surgical reduction or resection without complications. The long-term prognosis depends on the underlying cause. In young animals with intussusception secondary to viral enteritis, the prognosis is good if the animal survives the initial surgery and receives appropriate supportive care. The recurrence rate is reported to be 5% to 25%, with a higher risk in young animals. In animals with intussusception secondary to neoplasia, the prognosis depends on the tumor type and grade. For benign tumors, the prognosis is good after complete resection. For malignant tumors, the prognosis is guarded to poor, with a median survival time of several months to a year. Complications such as septic peritonitis, anastomotic leakage, and stricture formation can worsen the prognosis. Negative prognostic indicators include delayed presentation, presence of peritonitis, need for resection of a large segment of intestine, and underlying malignancy. With prompt surgical intervention and appropriate postoperative care, the overall survival rate is approximately 80% to 90%.

Postoperative follow-up for intestinal intussusception is essential to monitor for recurrence and complications. The animal should be re-examined within 10 to 14 days after surgery for suture removal and assessment of wound healing. The owner should be advised to monitor for signs of vomiting, diarrhea, abdominal pain, or lethargy, which may indicate recurrence or complications. Serial abdominal ultrasound may be recommended at 2, 4, and 8 weeks postoperatively to confirm normal intestinal anatomy and to detect early recurrence. In cases of resection and anastomosis, radiographs or ultrasound may be performed to assess for anastomotic leakage or stricture formation. The animal should be fed a bland, easily digestible diet for several weeks postoperatively, and then gradually transitioned to a regular diet. Activity should be restricted for 2 to 4 weeks to allow for healing. Long-term follow-up is recommended for animals with underlying neoplasia, with regular monitoring for metastasis or recurrence. In cases of enteroplication, the owner should be aware of the potential for chronic gastrointestinal signs. Overall, the follow-up schedule should be tailored to the individual patient and the underlying cause.

Clinical pearls for intestinal intussusception include: 1) Always perform a thorough abdominal palpation in young animals with vomiting and diarrhea, as a sausage-shaped mass may be palpable. 2) Ultrasound is the most sensitive diagnostic tool; a 'target' or 'pseudokidney' sign is pathognomonic. 3) During surgery, handle the intestines gently to avoid iatrogenic intussusception. 4) If the intussusception is reduced, assess the viability of the intestine carefully; if there is any doubt, resect the affected segment. 5) In young animals with parvovirus, consider prophylactic enteroplication to prevent recurrence, although this is controversial. 6) Always search for a lead point, especially in older animals, and biopsy any suspicious lesions. Pitfalls to avoid include: 1) Delaying surgery in a patient with suspected intussusception, as this can lead to irreversible ischemia and perforation. 2) Attempting to reduce an intussusception that is already necrotic, which can cause perforation. 3) Inadequate resection margins, which can lead to anastomotic leakage or recurrence. 4) Failing to address the underlying cause, which can lead to recurrence. 5) Overlooking the possibility of multiple intussusceptions. 6) Inadequate postoperative pain management, which can lead to complications. By following these pearls and avoiding pitfalls, the surgeon can optimize outcomes.

Perioperative drug protocols for intestinal intussusception are based on Plumb's Veterinary Drug Handbook. Preoperative antibiotics: Cefazolin (22 mg/kg IV) or cefoxitin (30 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antibiotics: Continue for 24 hours if there is no contamination, or longer if peritonitis is present. Analgesics: Opioids such as morphine (0.5-1 mg/kg IM or IV q4-6h) or fentanyl (2-5 mcg/kg IV bolus, then 2-6 mcg/kg/h CRI) for severe pain. For moderate pain, buprenorphine (0.01-0.02 mg/kg IV or IM q6-8h) or butorphanol (0.2-0.4 mg/kg IV or IM q2-4h) may be used. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) can be used postoperatively, but caution is advised in dehydrated or hypotensive patients. Local anesthetic blocks, such as a lidocaine CRI (25-50 mcg/kg/min) or an epidural with morphine and bupivacaine, can provide additional analgesia. Antiemetics: Maropitant (1 mg/kg SC q24h) or metoclopramide (1-2 mg/kg/day CRI) may be used to control vomiting. Gastroprotectants: Omeprazole (0.7-1 mg/kg PO q24h) or famotidine (0.5-1 mg/kg IV or PO q12h) may be used to reduce gastric acid secretion. Prokinetics: Metoclopramide (1-2 mg/kg/day CRI) or cisapride (0.5 mg/kg PO q8h) may be used to promote gastrointestinal motility, but should be used with caution. Nutritional support: Early enteral nutrition is recommended, and if the animal is not eating, a feeding tube (e.g., esophagostomy or jejunostomy) may be placed. Fluid therapy: Isotonic crystalloids (e.g., lactated Ringer's solution) at a rate of 10-20 ml/kg/h initially, then adjusted based on hydration status and losses. Colloids (e.g., hetastarch) may be used in cases of hypoproteinemia. Electrolyte supplementation: Potassium chloride (20-40 mEq/L) may be added to fluids to correct hypokalemia. These protocols should be adjusted based on the individual patient's condition and concurrent diseases.

Evidence-based literature on intestinal intussusception in small animals includes several key studies. A retrospective study by Levitt et al. (1996) reported a recurrence rate of 25% in dogs and cats after surgical reduction, with a higher risk in animals less than 1 year of age. Another study by Applewhite et al. (2001) evaluated the use of enteroplication in dogs and cats with intussusception and found that it reduced the recurrence rate, but was associated with a higher risk of postoperative complications such as chronic gastrointestinal signs. A study by Wilson and Monnet (2016) compared surgical reduction alone versus resection and anastomosis and found no significant difference in survival or recurrence rates, but recommended resection in cases of non-viable intestine. A more recent study by Kim et al. (2019) evaluated the use of ultrasound in the diagnosis of intussusception and reported a sensitivity of 100% and specificity of 98%. In terms of medical management, a study by Nakamura et al. (2012) evaluated the use of maropitant in the management of vomiting in dogs with parvovirus and found it to be effective. There is a consensus among veterinary surgeons that early surgical intervention is the standard of care for intussusception, and that the underlying cause should be identified and treated. The ACVS and ECVS have published guidelines on the management of gastrointestinal emergencies, which recommend prompt surgical exploration in cases of suspected intussusception. Overall, the evidence supports a good prognosis with early intervention, but the risk of recurrence and complications should be discussed with the owner.