True and false large bowel obstruction.

Acute large bowel obstruction can be the result of mechanical causes (such as colorectal cancer) or motility disturbances, the latter being termed colonic pseudo-obstruction. Whatever the aetiology, the pathophysiology of large bowel obstruction has clinical significance. Changes in motility augmented by increased colonic blood flow may play a role in dissemination of tumour cells and/or bacteria. Intravascular fluid depletion, especially shortly after intestinal decompression, has important haemodynamic implications. The diagnosis is often confirmed on plain abdominal X-ray, but water-soluble contrast studies are important in distinguishing a mechanical obstruction (which almost always requires an operation) from a pseudo-obstruction (which can usually be managed without surgery). Mortality and morbidity may be reduced by optimization of the patient's condition both before and after the operation using intensive care facilities and by careful timing of surgery. The surgical management of malignant large bowel obstruction is best directed by a senior surgeon. For tumours up to and including the splenic flexure, an extended right hemicolectomy is advisable since it offers adequate removal of the tumour and allows an immediate safe ileocolic anastomosis. More distal tumours should be resected if possible, and there is much to recommend on-table irrigation and immediate anastomosis, although a colostomy with a mucous fistula or Hartmann's procedure still have a place. Endoscopic diagnosis and decompression enables definitive surgery to be undertaken electively and several techniques are being evaluated. Non-operative reduction of sigmoid volvulus by rigid or flexible endoscopy is achieved with high success rates, but is not recommended for caecal volvulus. Resection is usually necessary in both to prevent recurrence. Mortality of colonic volvulus is closely related to bowel viability. Uncomplicated colonic pseudo-obstruction may be managed medically or by endoscopic decompression. It often occurs in association with systemic medical conditions, which need to be treated vigorously. Surgery is indicated if there are signs of impending or frank perforation, or if non-operative measures fail.