Introduction

Intussusception is defined as invagination of a segment of the gastrointestinal tract into the lumen of an adjoining segment. The intussusceptum is the invaginated segment whereas the intussuscipiens is the enveloping segment. Any portion of the alimentary tract may be affected but the ileo-colic junction is most commonly concerned.

Intussusception can be considered as a sign which is consequence of a gastro-intestinal disease. It occurs when increased motility (hyperperistaltism) of an intestinal tract segment runs toward a relaxed following segment. In such instances and most of the time, the intussusception occurs in a normograde direction. However the intussusception can occur in a retrograde direction. Reverse peristalsis may increase the length of intestine involved in the intussusception.

Any condition responsible for hyperperistaltism predisposes to intussusception (intestinal parasitism, infectious enteritis, metabolic disorders, foreign bodies, previous surgical procedure, intestinal masses). The original cause of the intussusception is often unclear.

Affected animals are younger than 1 year in 75% of the cases. When older animals are affected, the disease can be associated with intestinal neoplasia.

Initially, invagination causes partial intestinal obstruction, which may progress to complete obstruction. The main factor affecting bowel viability is the degree of constriction of the mesentery with the intestinal vessels between the inner and outer intussusceptum. In early stages of the intussusception, strangulation of venous return causes the invaginated intestine to become swollen and congested. In later stages, fibrinous exudation from the serosal surfaces of the congested intestinal segment causes them to adhere. Progressive constriction obstructs arterial flow and lead to necrosis and ischemia of the affected intestinal wall. Local peritonitis is often observed. Eventually intestinal devitalization occurs, with subsequent contamination of the abdominal cavity.

Chronic intussusceptions with minimal hemodynamic changes in the intestinal wall can be observed.

Diagnosis

Clinical Signs

The presenting signs in dogs and cats with intussusception are varied and nonspecific. Diagnosis of intussusception can be difficult in chronic forms. It should be suspected in young animals with unclear abdominal signs. Patients with chronic intussusception often have intractable, intermittent diarrhea, and hypoalbuminemia; intussusceptions and parasites are the two major causes of chronic protein-losing enteropathy in dogs less than 8 to 12 months of age. Other clinical signs include depression, anorexia, and emaciation.

Clinical signs of acute intussusceptions are those of intestinal obstruction. The severity and type of clinical signs depend on the location, partial or complete obstruction, vascular integrity, and duration of the intestinal obstruction. Bloody mucoid diarrhea, vomiting, abdominal pain, and a cylindrical palpable mass may occur with intussusceptions. A palpable abdominal mass has been reported in 53% of the cases. Tenesmus and hematochezia may be present in ileocaecocolic intussusceptions. Rectal prolapse of the invaginated segment can be observed. Rectal palpation should be performed to differentiated rectal prolapse and intussusceptions.

Imaging

Radiography of the abdomen may reveal signs of intestinal obstruction. These signs may not be present when the obstruction is partial or in chronic or intermittent intussusceptions. Jejunojejunal intussusception more often results in an obstructive pattern than does ileocolic intussusception. Increased soft tissue density may underline an abdominal mass. Barium studies are often reported as an aid to get a definitive diagnosis of intestinal obstruction. However since leakage of barium in the abdomen can induce severe peritonitis, it should be used with care when intestinal perforation is suspected or when a surgical procedure on the intestine is imminent.

Barium enema has been used in children to reduce enterocolic intussusceptions. It has been reported to be successful in one 5 month old shepherd dog but this may be just a coincidental finding on an intermittent intussusception.

Ultrasonography is widely recognized for diagnosis of intussusception. The ultrasonographic pattern of intussusceptions may vary with the quality of the image, the length of bowel involved, the duration of disease process and the orientation of the imaging plane in relation to the axis of the intussusception. In transverse ultrasonographic images, the juxtaposition of the wall layers of the intussuscipiens and inner and outer intussusceptum creates multiple hyperechoic and hypoechoic concentric rings that surround a hyperechoic center. This is often referred to as a target-like mass with 'multiple concentric rings sign'. In longitudinal images, multiple hyperechoic and hypoechoic parallel lines are usually observed. A multiplane imaging technique of the suspected intussusceptions is extremely critical to avoid misdiagnosis with other conditions that may mimic intussusception. Incompleteness of the periphery of the rings is used as a differentiating feature of the intestinal intussusception from other pathogenic conditions of the bowel.

Doppler ultrasonography has been used to predict the reducibility of an intestinal intussusception. Manual reduction was performed in 75% of intussusception (9/12) with blood flow in the mesenteric vessels. All dogs in the study that did not have color flow Doppler ultrasonographic signal had an irreducible intussusception at coeliotomy.

Treatment

Treatment of intussusceptions in dogs and cats is generally surgical. Occasionally percutaneous manual reduction of the intussusception may be successful and not recur. Surgical management involves either manual reduction or resection and anastomosis or both.

Exploratory laparotomy is performed on the ventral midline. The entire gastrointestinal tract is carefully examined because multiple intussusceptions can occur simultaneously. Manual reduction can be attempted by gently applying traction on the intussusceptum and pressure on the intussuscipiens. Care should be taken to avoid further vessel damage. The reduction can be successful when no or minor adhesions are present between bowel loops. Viability of the intestine is subjectively assessed by color, peristaltic activity, patency of blood vessels.

Enterectomy and anastomosis is performed when the affected segment is not reducible, not viable, perforated or when a mass lesion is responsible for the intussusception. In previous reports involving a total of 88 dogs, 82% required resection and anastomosis because of an inability to manually reduce the intussusception or avascular necrosis of the involved bowel.

When the intussusceptions cannot be reduced manually, an attempt is made to save as much length of healthy bowel as possible. Partial reduction is often possible and is performed. An enterotomy is performed on the antimesenteric border of the intussusceptum close to the inverted wall. The intussuscipiens is exteriorized. This usually helps in obtaining further reduction. The enterectomy is performed between the non reducible part of the intussuscipiens and the longest healthy portion of the intussusceptum. The enterotomy line is then routinely closed. This technique effectively preserves at least one third of the length of the bowel which would have been resected if the enterectomy have been performed on each side of the intussusception.

Complications

The most common complications following treatment of intussusception are recurrence, dehiscence of the intestinal anastomosis, ileus, intestinal obstruction, peritonitis and short bowel syndrome. With recurrence, the intussusception is usually proximal to the anastomotic site or the plicated section of the bowel. The rate of recurrence in dogs with intussusceptions, regardless of the type of surgical procedure, is reported to be between 11 and 20%. Several surgical techniques to prevent recurrence have been recommended in the past including Noble or Childs-Phillips plication, enteropexy.

Recurrence occurs generally between 24h and 5 days post surgery. Several reports underlined the fact that recurrence is not related either to the bowel segment affected or whether a simple reduction, enterectomy or enteroplication is performed at the initial surgery. The efficacy of plication as a prophylactic measure have not been demonstrated. Severe complications requiring a second surgical procedure following enteroplication have been reported in 19% (3/16) of the cases: intestinal obstruction, strangulation, obstruction and recurrence in dogs in which only a segment of small intestine was plicated.

When results of the 4 largest series are combined together, no dog (0/30) that underwent enteroplication of the small intestine from the duodenocolic ligament to the ileocolic junction had recurrence whereas 17% (11/63) of dogs that did not undergo enteroplication developed a recurrence. Some authors recommend that the entire intestine should be plicated, the bends in the intestine should be gentle and that plication sutures should be placed at intervals that prevent entrapment and strangulation of other portions of the bowel.

However the use of perioperative opioids for sedation and analgesia seems to have considerably reduced the recurrence rate in the latest studies. The incidence was reduced from 17 to 3 % in dogs undergoing experimental renal transplantation. It was hypothesized that the use of opioids result in increased tone of the small intestine with increased amplitude of the non propulsive rhythmic segmental contractions. This was believed to reduce or prevent local bowel wall inhomogeneity and segmental ileus therefore decreasing the likelihood of intussusception.