Large bowel obstruction
Large bowel obstruction is usually an acute blockage of the colon or rectum occurring in the elderly age group and requiring expeditious medical and surgical treatment. The urgency of management relates to the possibility of rupture of distended or compromised colon with the risk of faecal peritonitis. The three most common causes of mechanical obstruction are carcinoma of the colon, sigmoid volvulus and diverticular disease. Pseudo-obstruction (Ogilvie's syndrome), where there is acute dilatation of the colon without mechanical obstruction, presents with similar clinical features to an organic obstruction with the same potential complications, but is usually associated with some other illness.
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.
Aetiology of large bowel obstruction
Carcinoma of the colon or rectum
At least 50% of large bowel obstructions are due to carcinoma. The most common site is the sigmoid colon, accounting for 30% of all cases. This is not only because the sigmoid colon is a common site for colonic carcinoma, but also because the lumen is relatively narrow and the faeces are firm rather than liquid. The second most common site is the splenic flexure, where the combination of a sharp kink in the colon together with luminal narrowing by the tumour and relatively firm stools leads to blockage. Right-sided obstructions are less frequent because the caecum and ascending colon are relatively capacious and the faecal material is liquid. The features of a right-sided large bowel obstruction may be less obvious than those of left-sided colonic lesions because only a small proportion of the colon is distended. An obstruction at the ileocaecal valve will produce features of a low small bowel obstruction.
In Western countries sigmoid volvulus is essentially a condition of the elderly and frail, often with a long history of constipation and laxatives. In Africa, however, younger age groups can be afflicted and this is probably associated with the very high fibre dietary intake. Caecal volvulus is relatively uncommon and tends to occur in the younger age group. Volvulus of the colon involves twisting of the bowel on its mesentery, leading to ischemia and subsequent risk of perforation of the volved portion of the bowel and the caecum if it becomes overdistended because of unrelieved obstruction.
Diverticular disease can involve any part of the colon but in the vast majority of instances the sigmoid colon is most severely affected. Diverticulosis with subsequent scarring as well as muscular wall hypertrophy can cause stricturing of the colon, which can lead to large bowel obstruction and can be confused with carcinoma.
Less common causes
Less common causes of mechanical large bowel obstruction include stricturing as a result of inflammatory bowel disease (both ulcerative colitis and Crohn's disease) as well as ischaemic and radiation strictures, intussusceptions, adhesions (much more likely to cause a small bowel obstruction) and faecal impaction. Faecal impaction occurs when a faecal mass cannot be evacuated and it can affect any age group, but most commonly occurs in the elderly. The symptoms may be those of inability to evacuate, but not infrequently and paradoxically patients will present with faecal incontinence. This is because the impacted faecal bolus relaxes the rectosphincteric reflex and more proximal liquid stool escapes around the faecal bolus.
Pseudo-obstruction (Ogilvie's syndrome)
Pseudo-obstruction is a form of ileus of the large intestine, and in most patients is associated with some other ongoing medical condition. It tends to affect the older generation, and the symptoms and potential complications are essentially the same as those due to mechanical large bowel obstruction, including perforation. It is believed that the associated medical condition or metabolic abnormality may cause an imbalance of the autonomic nervous system, with a predominance of sympathetic activity.
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/or 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) (Grossly distended caecum with incipient perforation.) 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. (Gastrografin enema showing obstructed descending colon.) 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.
Management of large bowel obstruction (Management of suspected large bowel obstruction.)
Immediate surgery will be required if the patient has overt peritonitis. Such immediate management, however, will usually depend on the result of a water-soluble contrast enema. If a mechanical obstruction is present then it is most likely due to a colonic carcinoma. For a distal obstruction (most commonly a sigmoid carcinoma) where obstruction is complete, relatively urgent surgery is necessary. Conventionally the most common approach would be a three-staged surgical management. The first stage is establishment of a proximal colostomy followed within weeks by a second stage involving resection and anastomosis, and finally some weeks or months later the closure of the colostomy.
A one-stage resection and anastomosis has been considered hazardous because, in general, the patients are elderly and often with co-morbidities. There is usually luminal disparity making anastomosis difficult and the proximal colon is loaded with faeces, which may increase the risk of anastomotic disruption. Recently, however, with improvement in resuscitation and anaesthesia the introduction of a one-stage resection and anastomosis, most often with on-table total colonic lavage to remove faecal material, has been demonstrated as safe and is a technique being used more frequently. Any perforation or sepsis at the site of the carcinoma mandates resection of the lesion, establishment of a sigmoid colostomy and oversewing of the rectal stump (Hartman's procedure). A second stage is done at a later time to re-establish bowel continuity.
Obstructing carcinoma of the splenic flexure and more proximal colon, including the transverse and ascending colons as well as the caecum, will usually be dealt with by a resection and end-to-end ileocolonic anastomosis. In this operation the tumour and all of the proximal distended colon is resected, and the well vascularised and relatively healthy ileum is suitable for anastomosis to the collapsed distal large intestine. Some patients may not be well enough for this onestage procedure and still require a proximal stoma.
Self-expandable metal stents are now being used more widely in the management of malignant low left-sided large bowel obstruction. These stents are placed endoscopically under fluoroscopic control through the obstructing lesion (Metallic stenting of an obstructing carcinoma of the sigmoid colon.) and can remain in place for a prolonged period where the stent is definitive palliative treatment or alternatively can decompress the colon so that within some weeks a one-stage resection and anastomosis may be possible. The stents are expensive but they appear to be cost-effective. Complications of perforation and bleeding are possible but uncommon, and it is likely this technique will be used more widely in the future.
In the first instance after diagnosis of the sigmoid volvulus endoscopic decompression should be attempted. This can be performed with a rigid sigmoidoscope or a colonoscope. Such decompression can be achieved in most instances. If it is performed with a colonoscope it has the advantage of potentially being able to decompress the proximal colon. Endoscopic decompression is not without risk as the instrument then being passed through the spiral lumen at the level of the volvulus may perforate the colon, particularly if there is an area of ischaemia. If decompression is successfully achieved it may be useful to pass a long flatus tube through the lumen of a rigid sigmoidoscope to ‘splint’ the sigmoid colon in the hope of preventing early recurrence. Unfortunately, recurrence tends to occur in about half of the patients. Under these circumstances surgical resection with either end-to-end anastomosis or a Hartman's procedure is required. In general, if the acute situation is successfully dealt with by decompression, then an elective sigmoid colostomy should be performed when the patient's physical condition has improved and the bowel is deflated.
In general, the principles of surgical management applicable to obstructing carcinoma of the sigmoid colon apply to obstruction due to a diverticular stricture. A definitive resection, whether it is performed at the time of the initial resection of the stricture (i.e. a Hartman's procedure) or if there is an end-to-end anastomosis, will usually require complete resection of the sigmoid colon to effectively eradicate the diverticulosis. Any sepsis in association with the diverticular stricture, such as a perforation or contained abscess, will usually mandate resection and a Hartman's procedure, although in some instances drainage of sepsis and a temporary proximal defunctioning stoma may be appropriate.
Pseudo-obstruction (Ogilvie's syndrome)
If a gastrografin enema confirms the diagnosis of pseudo-obstruction, provided there is no evidence of colonic perforation, which would mandate urgent surgical intervention, then conservative measures which address the patient's general medical condition including fluid and electrolyte balance are required. If rectal examination or sigmoidoscopy achieve the passage of flatus then this should be carried out three or four times each day to continue to decompress the colon. About half the patients with pseudo-obstruction may respond to this management, but if not then neostigmine, which is a potent parasympathomimetic, should be administered intravenously. Such treatment has the potential for complications, including cardiac arrhythmias and perforation if there happens to be mechanical obstruction. If sigmoidoscopy and neostigmine or other prokinetic agents such as erythromycin or cisapride are unsuccessful, then colonoscopic decompression should be attempted. This is likely to be successful, but without bowel preparation may be dangerous. Satisfactory decompression may be achieved in most patients, but there is a significant recurrence rate. If these measures fail then the establishment of a colostomy or caecostomy may be required.
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