Causes of LBO include: tumors, torsion and fecal impaction. The vast majority of colorectal tumors that cause obstruction are colon and rectal cancers of the left half; a few are benign tumors, such as lipomas and large polyps, that cause obstruction due to intussusception (intussusception). The common site of colonic intussusception is the sigmoid colon or cecum, with the former mostly seen in the elderly and the latter mostly seen in young people. Fecal impaction is most often seen in older adults with constipation. Occasionally, the sigmoid colon herniates into the left inguinal canal and becomes entrapped, resulting in obstruction. Intestinal stricture due to diverticulitis and ischemic colitis is also a common cause of LBO in European and American patients, mostly in the sigmoid colon. Unlike small bowel obstruction, colonic obstruction due to adhesions is rare. Sometimes, inflammation and tumors adjacent to the colon can also cause extracolonic pressure obstruction, such as peripancreatic inflammation due to acute pancreatitis can lead to scarring stenosis of the transverse colon, and recurrence of gastric cancer after surgery can also infiltrate the transverse colon. Except for intestinal torsion, LBO is almost never strangulated; however, the proximal colon of the obstruction can be highly dilated, and there is a risk of rupture when the cecum exceeds 12 cm in diameter. With the exception of intestinal torsion, the symptoms of LBO are usually gradual and present as progressively increasing abdominal distention with cessation of defecation. If the ileocecal valve is intact, there may be no vomiting; if the ileocecal valve is open, the colonic contents may reflux into the ileum and fecal vomiting may occur. Most patients do not have abdominal pain, thus, patients tolerate it better than small bowel obstruction; sometimes abdominal pain can occur due to fecal impaction; the presence of unexplained severe abdominal pain, tachycardia, shock or fever in LBO requires consideration of the possibility of intestinal perforation or strangulation. In the case of intestinal torsion, the onset is sudden, and if the diagnosis is delayed, strangulation and necrosis may occur due to insufficient blood supply. A detailed medical history should be taken in all cases of LBO, especially in the case of bowel movements. If the stool habits and traits change, and if pus and blood stools appear, the possibility of colorectal cancer should be considered; in elderly people with constipation, fecal impaction and sigmoid torsion may occur. Chronic weight loss suggests the possibility of colorectal cancer. Physical examination shows that the abdomen is bulging, there is usually no pressure pain in the abdomen, sometimes the tumor at the site of obstruction can be palpated, bowel sounds are generally normal, rectal finger examination may find anal stenosis, low rectal cancer and fecal mass embolism, etc. The inguinal canal and femoral canal area should be exposed during abdominal examination to avoid missing the embedded hernia. If signs of peritonitis are present, it suggests intestinal perforation or necrosis. LBO causes fever and elevated WBC more often than small bowel obstruction because the number of bacteria and other microorganisms in the large intestine is considerably higher than in the small intestine. Anemia, too, suggests the possibility of colorectal cancer. Imaging for LBO is mandatory, X-rays are used for primary screening and CT is recommended. In mechanical colonic obstruction due to colorectal cancer, CT may reveal irregular thickening of the intestinal wall or find an occupying mass, and the site of obstruction can be clearly determined with a highly dilated proximal colon containing a large amount of loose stool and less gas; the presence of metastases, ascites or other conditions can also be observed; sometimes, a constricted tumor may not be seen as an occupancy, but a sudden deflation of the distal intestinal canal will be found; if this cannot be identified, barium enema helps the diagnosis of mechanical obstruction. In addition to noninvasive imaging, in patients with unclear diagnosis and without urgent surgery, colonoscopy or barium enema can be performed to clarify the diagnosis and help to exclude pseudo-obstruction of the colon, if conditions allow. In patients with colorectal cancer, barium enema can show filling defects and strictures at the site of obstruction, and sigmoid colon torsion is usually seen in the elderly, and the torsion site shows the typical bird-beak sign during barium enema. In addition to its diagnostic role, endoscopy also has a therapeutic role, including endoscopic repositioning for sigmoid torsion and endoscopic dilation for stent placement to relieve obstruction. Once diagnosed, mechanical obstruction of the large intestine should be treated with dietary suppression and fluid replacement to maintain fluid and electrolyte balance. Gastrointestinal decompression can prevent vomiting and vomiting-induced aspiration and is indicated in cases of ileal valve opening regurgitation. Other non-surgical measures include anti-infective therapy and treatment of comorbidities. Laxatives are contraindicated in complete obstruction and may be tried with caution in incomplete LBO due to fecal masses. A preliminary etiologic diagnosis can be obtained in most cases by preoperative evaluation, and most of these cases require surgical treatment. Colorectal cancer is a common cause of LBO (about 60% of cases). Right hemi-colonic tumors causing obstruction are rare, and if this occurs, a right hemi-colonic resection with one-stage anastomosis or, if poor anastomotic healing is expected, an ileostomy proximal to the anastomosis should be performed. If the degree of obstruction is not severe, the difference in anastomotic caliber is not large, and the intestinal canal is in good condition, after intestinal decompression and/or intraoperative intestinal irrigation, one-stage anastomosis can also be performed, and if necessary, intestinal fistula can be performed at the proximal end of the anastomosis. In rare cases, the tumor may be temporarily unresected and only a diversionary fistula may be performed, for example, when the patient has delayed surgery leading to shock or vital organ failure, when the tumor infiltrates the adjacent organs and cannot be resected, or when the IV cancer is present. Endoscopic dilated stenting is strictly indicated for high-risk cases in which the bowel lumen is almost blocked but a small amount of bowel lumen is still allowed to pass; its advantage is that it avoids colostomy and creates the conditions for subsequent stage 1 resection of the tumor (or stage 1 resection after neoadjuvant therapy) with anastomosis. However, stenting has the potential for reocclusion, and this technique is only suitable for palliative care in high-risk patients who are temporarily unfit for surgery, or as a pre-resection preparation, and requires an experienced endoscopist to perform. Large adult intussusceptions are most often caused by tumors and should not be attempted non-surgically, nor intraoperatively, and should be performed with segmental resection or hemicolectomy. Most fecal impaction occurs in the rectum, and the diagnosis can be made by rectal finger examination; CT scan provides more direct evidence and can exclude the diagnosis. Removal of the stool with fingers and cleansing enemas can mostly relieve the obstruction. If the stool forms hard stones leading to complete obstruction (usually in the sigmoid colon), especially if barium is mixed with it, open surgery is indicated after non-surgical treatment has failed. The treatment of cecum torsion can be performed by both resection of the intestinal segment with a one-stage anastomosis and repositioning of the cecum with a cecostomy. In cases of sigmoid torsion, endoscopic or anal canal repositioning or direct intestinal resection and anastomosis can be performed, and recurrence is almost inevitable if only repositioning is performed.