Intussusception

Diagram of intussuscception (Courtesy of Elspeth Milne)

Description

Intussusception is the invagination of one portion of the gastrointestinal tract into the lumen of the adjacent portion. The intussusceptum is the invaginated segment and the intussuscipien is the enveloping segment.

Intussusception results from abnormal peristalsis. Vigorous contractions force a segment of intestine to teloscope into the lumen of a more relaxed adjacent segment. A normograde intussusception is most common, but retrograde intussusception has also been reported.

Intussusceptions can be classified according to their location in the gastrointestinal tract. They occur more commonly in regions where there is a significant change in lumen diameter, such as ileocolic and gastroesphageal junctions. Ileocolic intussusceptions are most common they frequently protrude from the rectum and must be distinguished from a rectal prolapse. In the case of an intussusception, it is possible to pass a probe next to the anus, but not in rectal proplapse.

Initially, a partial obstruction results. Overtime, this progresses to a complete obstruction, with obstruction of venous return, arterial occlusion and avulsion of vessels. The intestinal walls become oedematous, ischaemic and turgid, resulting in devitalisation if not treated. Adhesion can occur in long standing cases due to fibrin deposition.

Pathogenesis

Intersusception (Courtesy of Bristol BioMed Image Archive)

The proximal intestine invaginates into the adjacent distal portion, taking its mesenteric attachment with it. Compression of the mesenteric vessels obstructs venous drainage of the gut, resulting in venous congestion, leading to swelling and oedema. An inflammatory exudate is released from the serosal surface, fibrinous adhesions may form between surfaces making the structure irreducible this may progress to necrosis of the tissue. There is functional obstruction to bowel. May rupture, leading to peritonitis and death. Intussusception normally occurs due to gastrointestinal disease, although it is often hard to identify the cause. Parasites, infectious enteritis, metabolic disorders, foreign bodies, history of recent intestinal surgery, intestinal masses have all been known to associate with intussusception. Chronic intussusception can occur with little haemodynamic changes.

• Associated with any condition that increases peristalsis
  • Enteritis
  • Foreign body
  • Heavy parasitism
  • Previous intestinal surgery
  • Intramural abscess/tumour
  • Motility disorders.
  • Change in diet
  • Bacterial infection

Signalment

Intussusception most commonly affects young animals. In order animals, it may be occur due to neoplasia or agonal changes.

• Occur most commonly in dogs
• 75% of cases affect animals under one year of age
• Breed predisposition:

Diagnosis

Clinical Signs

Acute Intussusception

• Vomiting
• Diarrhoea; bloody mucoid faeces
• Abdominal pain
• Palpable sausage-shaped mass in the abdomen
• Tenesmus; in cases of ileocaecocolic intussusception
• Haematochezia; in cases of ileocaecocolic intussusception

Chronic Intussusception

• Intermittent diarrhoea
• Depression, anorexia and emaciation

Diagnostic Imaging

Radiography

• Plain abdominal radiography may reveal obstruction in the intestines. This, however, may not be present in cases of partial, chronic or intermittent intussusception. Jejunojejunal intussusception is reported to show signs of obstruction more commonly compared to ileocolic intussusception. A mass may be seen on radiograph.
• A barium enema or upper gastrointestinal contrast study can be useful in identifying the site of obstruction. This should be used with care as leakage of contrast into the abdominal cavity will result in peritonitis.

Ultrasonography

Abdominal ultrasound is a good diagnostic tool for intussusception. On a transverse section, a hyperechoic target mass in the centre with multiple hyperechoic and hypoechoic concentric ring is seen. On a longitudinal section, multiple hyperechoic and hypoechoic lines are seen. The intestines may also be hypomotile and proximal fluid accumulation can occur.

Colonoscopy

This can be used to identify ileocolic or caecocolic intussusception.

Intussusception can occur in the small intestine, caecum or colon.

Pathology

The degree of damage to the intestine depends on the severity of the intussusception. In severe or chronic cases fibrinous adhesions form between surfaces making the structure irreducible. Necrosis of the tissue usually follows.

Intussusception may occur due to post mortem change, in this case there are no other associated changes and the invaginated intestine is easily reducible.

Treatment

Occasionally the intussusception can be reduced manually through the skin.

Medical

Fluid therapy and correction of electrolyte and acid-base abnormalities should be carried out prior to surgical correction.

Surgery

Surgery is usually required to manually reduce the intussusception, it may be necessary to resect and anastomose the intestine in cases where adhesions have formed. This decision depends on the viability of the intestines, as determined by the colour, vascular supply and presence or absence of peristalsis. Complications include dehiscence at the site of anastomosis, peritonitis, recurrence (11-20%, most common within 1-5 days post surgery), ileus, intestinal obstruction and short bowel syndrome. Recurrence can be treated with motility altering drugs or intestinal pexy or plication. It is important to preserve as much of the intestine as possible to avoid short bowel syndrome.

Prognosis

This depends on the location, completeness and duration of the intusussception. The prognosis is good in animals treated with early surgical intervention and aggressive supportive care. The prognosis is poor for animals with perforated intestine and peritonitis.

References

• Barreau, P. (2008) Intussusception: Diagnosis and Treatment 33rd WSAVA Congress
• Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company.
• Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier
• Hall, E.J, Simpson, J.W. and Williams, D.A. (2005) BSAVA Manual of Canine and Feline Gastroenterology (2nd Edition) BSAVA
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.