It is said that adhesions never cause large bowel obstruction. Indeed it is rare to encounter such a patient, however, as usual in surgery never say never. Even though it is not uncommon to find the sigmoid colon in large left sided inguino-scrotal hernias, I have never seen a patient with large bowel obstruction due to an inguinal or femoral hernia. The main cause of large bowel obstruction is cancer of the colon.
The major site for large bowel obstruction due to cancer is in the vicinity of the recto-sigmoid junction. One may also commonly, see obstruction due to cancer from the hepatic flexure distally. Obstruction due to tumors proximal to this is unusual unless they directly obstruct the ileo-caecal valve. The following are the main reasons for this observation;
Large bowel obstruction may be due to volvulus. In this case the obstruction is due to a twisting of the bowel. The main site is the sigmoid colon. Less than 1 in 20 cases of large bowel obstruction are due to sigmoid volvulus. Volvulus may also affect the caecum. This cause of obstruction is commoner is Africa than in Europe. In Ireland most patients with Sigmoid volvulus are elderly and many suffer from chronic constipation. The typical patient is an elderly psychiatric patient.
One may suspect sigmoid volvulus based upon the presentation of the typical patient. Plain radiology will usually show a hugely dilated loop of bowel which points away from the site of the mesenteric attachment.
The patient is best brought to theatre for attempted endoscopic (per anal) reduction of the volvulus. If the mucosa looks purple or reduction is not possible, the patient proceeds to laparotomy.
Pelvic tumors may cause large bowel obstruction bye encircling the rectum. Thus peritoneal deposits from any tumor in the pelvis may cause obstruction. Alternatively, direct extension from urological or gynecological malignancies may cause intestinal obstruction.