Large bowel obstruction
Causes of large bowel obstruction include:
Neoplasms / cancer
Diverticulitis / Diverticulosis
Hernias
Inflammatory bowel disease
Colonic volvulus (sigmoid, caecal, transverse colon)
Adhesions
Constipation
Fecal impaction
Fecaloma
Colon atresia
Intestinal pseudoobstruction
Endometriosis
Narcotic induced (especially with the large doses given to cancer or palliative care patients)

Outlet obstruction
Outlet obstruction is a sub-type of large bowel obstruction and refers to conditions affecting the anorectal region that obstruct defecation, specifically conditions of the pelvic floor and anal sphincters. Outlet obstruction can be classified into four groups. Functional outlet obstruction
Inefficient inhibition of the internal anal sphincter
Short-segment Hirschsprungs disease
Chagas disease
Hereditary internal sphincter myopathy
Inefficient relaxation of the striated pelvic floor muscles
Anismus (pelvic floor dyssynergia)
Multiple sclerosis
Spinal cord lesions
Mechanical outlet obstruction
Internal intussusception
Enterocele
Dissipation of force vector
rectocele
Descending perineum
Rectal prolapse
Impaired rectal sensitivity
Megarectum
Rectal hyposensitivity

Diagnosis
The main diagnostic tools are blood tests, X-rays of the abdomen, CT scanning, and ultrasound. If a mass is identified, biopsy may determine the nature of the mass.Radiological signs of bowel obstruction include bowel distension and the presence of multiple (more than six) gas-fluid levels on supine and erect abdominal radiographs. Ultrasounds may be as useful as CT scanning to make the diagnosis.Contrast enema or small bowel series or CT scan can be used to define the level of obstruction, whether the obstruction is partial or complete, and to help define the cause of the obstruction.
Signs and symptoms
Depending on the level of obstruction, bowel obstruction can present with abdominal pain, swollen abdomen, abdominal distension, and constipation. Bowel obstruction may be complicated by dehydration and electrolyte abnormalities due to vomiting; respiratory compromise from pressure on the diaphragm by a distended abdomen, or aspiration of vomitus; bowel ischemia or perforation from prolonged distension or pressure from a foreign body.In small bowel obstruction, the pain tends to be colicky (cramping and intermittent) in nature, with spasms lasting a few minutes. The pain tends to be central and mid-abdominal. Vomiting may occur before constipation.In large bowel obstruction, the pain is felt lower in the abdomen and the spasms last longer. Constipation occurs earlier and vomiting may be less prominent. Proximal obstruction of the large bowel may present as small bowel obstruction. Causes
Small bowel obstruction
Causes of small bowel obstruction include:
Adhesions from previous abdominal surgery (most common cause)
Barbed sutures
Pseudoobstruction
Hernias containing bowel
Crohns disease causing adhesions or inflammatory strictures
Neoplasms, benign or malignant
Intussusception
Volvulus
Superior mesenteric artery syndrome, a compression of the duodenum by the superior mesenteric artery and the abdominal aorta
Ischemic strictures
Foreign bodies (e.g. gallstones in gallstone ileus, swallowed objects such as expandable water toys)
Intestinal atresiaAfter abdominal surgery, the incidence of small bowel obstruction from any cause is 9%. In those where the cause of the obstruction was clear, adhesions are the single most common cause (more than half).