Large bowel obstruction
Clinical features of large bowel obstruction
The typical clinical features are:
_ Abdominal pain due to distension and colic.
_ Abdominal distension due to retention of faeces and flatus.
_ Constipation, and in a complete obstruction this will be absolute, ie. without the passage of faeces or flatus.
_ Peritonism if perforation has occurred.
_ Vomiting can be a late symptom.
Examination and investigations
Examination of a patient with a typical large bowel obstruction will reveal a distended and tender abdomen, often worst in the right iliac fossa because of caecal distension. Guarding or peritonism will be present if there has been vascular compromise or perforation of the colonic wall. The abdomen is highly tympanitic to percussion, with high-pitched bowel sounds. An abdominal mass might be present but the distension may prevent it being palpable. Digital rectal examination and sigmoidoscopy may reveal a rectal or sigmoid carcinoma or tell-tale blood within the lumen of the bowel indicative of a higher lesion. Sometimes a ‘corkscrew sign’ may be detected at sigmoidoscopy, suggesting volvulus or torsion of the sigmoid colon. The differential diagnosis should include tense ascites and gross bladder distension secondary to urinary retention. A patient with a late large bowel obstruction may be dehydrated and toxic because of vomiting or peritonitis. Peritonitis with a large bowel obstruction is a serious complication with a high mortality rate due to faecal peritonitis, most likely as a result of perforation of the caecum (as a result of Laplace’s Law) (Fig. 20.1) or at the site of the obstruction, particularly at the point of torsion in a sigmoid volvulus.
The key investigation to be performed urgently is a plain X-ray of the abdomen, which will confirm marked colonic distension. A gastrografin enema should differentiate between a mechanical obstruction and colonic pseudo-obstruction. (Fig. 20.2) This differentiation is important as it will determine management. A plain X-ray may reveal the typical features of a sigmoid volvulus, with a distended sigmoid colon in the right upper quadrant. Free intraperitoneal gas indicates colonic perforation. A water-soluble contrast enema should define the level of the obstruction and in most instances the nature of the obstructing lesion. Sometimes the use of such water-soluble contrast enemas can be therapeutic by dislodging faeces from a narrowed large bowel lumen. Ultrasound examination of the liver and CT scanning of the abdomen and pelvis may also be useful in determining the presence of occult malignancy and aiding in management planning. Routine haematology and medical assessment is indicated, as in most instances surgical intervention is required.