Obstruction is most likely to occur in the small intestine or at the ileocaeco-colic junction and only very rarely in the large intestine. Foreign bodies are most frequently involved but obstruction may be caused by tumours, intussusceptions, congenital or acquired strictures or paralytic ileus.
Foreign body obstruction is most likely to occur in dogs with a history of eating rubbish or stones. Foreign bodies in cats are rare but when they do occur may involve fish hooks, fish bones or linear foreign bodies such as string. Adenocarcinoma is the most likely tumour to obstruct the intestine as it often grows into the lumen, unlike lymphosarcoma which usually causes annular thickening of the intestinal wall. Intussusceptions most frequently occur at the ileocaecocolic junction with small intestine telescoping into the colon.
Intestinal obstruction: Clinical diagnosis
Clinical signs depend to some extent on the location of the obstruction. Those which occur in the proximal small intestine are often manifest by acute persistent vomiting with faeces being passed initially often diarrhoeic in nature. Any blood in the faeces is likely to be dark and tarry in consistency. Obstructions in the distal small intestine will also cause vomiting, but not so acutely as proximal obstructions. Formed or diarrhoeic faeces will be passed for a short time before ceasing altogether. The authors have observed dogs where partial obstruction has occurred with a history of intermittent vomiting and diarrhoea.
Where an intussusception is present, vomiting may be seen together with the passage of faeces which rapidly become reduced in volume and bloody, resembling redcurrant jelly. Tenesmus is also observed in some cases of intussusception. Adenocarcinomas may partially block the intestine before causing complete obstruction. The clinical signs may therefore vary and may give the impression of a chronic problem rather than a sudden acute obstruction. Ulceration is quite common so that faeces may contain altered or fresh blood.
In all cases the animal will not only exhibit vomiting and diarrhoea but also dehydration, anorexia and depression and may develop abdominal pain. Palpation of foreign bodies can be difficult due to the free movement of intestinal loops in the abdomen. Intussusceptions are often palpable as fairly static hard sausage-shaped structures in a more fixed position. Tumours, if small, may be difficult to palpate in the early stages.
Radiographs will detect radiodense foreign bodies without difficulty, but radiolucent foreign bodies may be missed. However a large gas cap should be visible and possibly evidence of gravel collection within the intestine just proximal to the obstruction (). Barium should be used with care where obstruction is suspected, because if the bowel is perforated, barium will enter the peritoneum from where it will not be resorbed- In cases where perforation is suspected Gastrografin (Schering Chemicals) which can be resorbed should be used; this gives an equally satisfactory contrast.
Intestinal obstruction: Treatment
In all the cases described above, surgical intervention is required to correct the problem. No medical treatment is likely to be successful and the longer the foreign body lies in the bowel the more likely it is that perforation will occur with ensuing peritonitis and death. Liquid paraffin should be used with great care as it may move the foreign body further along the intestine, only to block at the ileocaccocolic junction.
The removal of adenocarcinomas is quite feasible especially it detected early before adhesions have formed or metastasis has occurred. Complete resection of a portion of intestine is feasible in some cases with end-to-end anastomoses of healthy tissue.
Intussusceptions may be reduced in the early stages before fibrous adhesions have formed. If they are diagnosed late then complete resection of the ileocaecocolic region with small and large intestine may be required. End-to-end anastomosis of the small and large bowel is feasible especially if there is an adequate length of intestine left for normal function.