Bowel Obstruction
A bowel obstruction is a blockage that prevents the normal passage of intestinal contents through the small bowel or colon. It can be mechanical—caused by a physical barrier such as scar tissue, a hernia, a tumor, or a twisted segment of bowel—or functional, in which the bowel stops moving effectively without any physical blockage (ileus or pseudo-obstruction). The classic presentation is crampy abdominal pain, vomiting, abdominal distension, and inability to pass gas or stool, though the pattern varies with the level and completeness of the blockage. Bowel obstruction is a common cause of emergency hospital admission and a leading reason for urgent abdominal surgery. CT of the abdomen and pelvis is central to diagnosis, identifying the site and cause of the blockage and, critically, distinguishing obstructions that can be managed conservatively from those that require prompt operation.
What is it?
The intestine normally moves its contents forward through coordinated waves of muscular contraction. A bowel obstruction occurs when that forward movement is blocked. Contents accumulate above the blockage, the bowel distends, fluid and gas build up, and a cascade of consequences follows—vomiting, dehydration, electrolyte disturbance, and, if pressure or vascular compromise progresses, loss of blood supply to the bowel wall.
The first and most important distinction is between mechanical obstruction and functional obstruction.
Mechanical obstruction involves a physical barrier. It may be caused by something outside the bowel compressing or tethering it (adhesions, hernias, external tumors), something within the wall (tumors, strictures from Crohn’s disease or prior radiation, inflammatory narrowing), or something inside the lumen (impacted stool, a gallstone that has eroded into the bowel, a swallowed foreign body, a bezoar, or intussusception, in which one segment telescopes into another).
Functional obstruction—also called ileus or, in the colon, acute colonic pseudo-obstruction (Ogilvie syndrome)—involves no physical blockage at all. The bowel simply stops propelling contents effectively. Postoperative ileus after abdominal surgery is the most familiar example. Other triggers include electrolyte abnormalities (particularly low potassium), opioid and anticholinergic medications, severe infection, retroperitoneal or spinal pathology, and critical illness. The clinical picture can closely mimic mechanical obstruction, which is one reason imaging matters: the treatments differ substantially, and operating on an ileus is not helpful.
The second distinction is the level of the obstruction. Small bowel obstruction is far more common, accounting for roughly three-quarters of mechanical obstructions. Adhesions—bands of internal scar tissue formed after previous abdominal or pelvic surgery—are the leading cause in adults in countries where abdominal surgery is common, and they can cause obstruction decades after the original operation. Hernias are the next most common cause and the leading cause worldwide in populations with less surgical history. Crohn’s disease strictures, small bowel tumors, radiation-induced strictures, and adhesions from prior peritonitis account for most of the remainder.
Large bowel obstruction is less common and has a different causal profile. Colorectal cancer is the leading cause, which is why a new large bowel obstruction in an adult prompts evaluation for malignancy. Volvulus—twisting of a segment of colon on its mesentery, most often the sigmoid and less often the cecum—is the next most common, and diverticular strictures, fecal impaction, and inflammatory or ischemic strictures account for much of the rest.
The third distinction, and the one that most directly determines urgency, is whether the obstruction is simple or strangulated. In a simple obstruction, flow is blocked but the blood supply to the bowel remains intact. In a strangulated obstruction, the blood supply is compromised—usually because the bowel is twisted, trapped in a hernia, or caught in a closed loop—and the bowel wall begins to die. Strangulation can progress to necrosis and perforation within hours and is a surgical emergency. A closed-loop obstruction, in which a segment is blocked at both ends, is particularly dangerous because pressure rises rapidly within the trapped segment with no outlet for decompression.
Symptoms follow a fairly predictable pattern determined by the level and completeness of the blockage.
Abdominal pain is typically crampy and intermittent, arriving in waves as the bowel contracts against the blockage. Pain that becomes constant, severe, and localized is a warning sign for ischemia or perforation rather than a normal evolution.
Vomiting timing reflects the level. A high (proximal small bowel) obstruction produces early, frequent, often bilious vomiting with relatively little distension. A distal small bowel or colonic obstruction produces later vomiting that may become feculent in character, with more pronounced distension.
Abdominal distension is more marked the more distal the blockage, because a greater length of bowel lies upstream to fill.
Obstipation—the inability to pass either gas or stool—characterizes complete obstruction. In partial obstruction, some gas and liquid stool may continue to pass, and patients sometimes report diarrhea, which can be misleading.
Additional findings include nausea, loss of appetite, dehydration, and bowel sounds that are initially high-pitched and hyperactive as the bowel strains against the blockage, then diminish and eventually disappear as it fatigues.
Signs suggesting strangulation, ischemia, or perforation include constant rather than crampy pain, fever, rapid heart rate, localized or generalized tenderness with guarding or rigidity, and signs of systemic illness. These warrant immediate evaluation.
Diagnosis combines history, examination, imaging, and laboratory studies.
CT of the abdomen and pelvis with intravenous contrast is the primary test. It confirms the presence of obstruction by demonstrating dilated bowel proximal to a transition point with collapsed bowel beyond it, identifies the underlying cause in most cases, distinguishes partial from complete obstruction, and—most importantly—assesses for features suggesting compromised bowel viability, including reduced bowel wall enhancement, wall thickening, mesenteric fat stranding, free fluid, pneumatosis (gas within the bowel wall), and gas in the portal venous system. CT also identifies closed-loop configurations and the whirl sign of volvulus, and detects free intraperitoneal gas indicating perforation. Oral contrast is often omitted in the acute setting because fluid already within the obstructed bowel provides natural contrast.
Abdominal X-rays are inexpensive and quick and may show dilated loops of bowel with air-fluid levels, but they are considerably less sensitive than CT, frequently cannot identify the cause or level, and cannot reliably assess bowel viability. They are increasingly used as an initial screening study rather than a definitive test.
Water-soluble contrast studies have both a diagnostic and a therapeutic role in adhesive small bowel obstruction. Contrast given by mouth or nasogastric tube that reaches the colon within a defined interval predicts a high likelihood of resolution without surgery, and the hyperosmolar contrast agent itself appears to promote resolution by drawing fluid into the lumen and reducing bowel wall edema.
Ultrasound is useful in children—particularly for intussusception, where it is the test of choice—and during pregnancy, where radiation avoidance is a priority. MRI is an alternative cross-sectional option in pregnancy.
Blood tests do not diagnose obstruction but assess its consequences and severity. A complete blood count may show hemoconcentration or leukocytosis, electrolytes and kidney function reveal the degree of dehydration and metabolic derangement (a hypochloremic, hypokalemic metabolic alkalosis is characteristic of prolonged vomiting), and lactate may be elevated with bowel ischemia—though a normal lactate does not exclude it, particularly early.
Colonoscopy has a role in selected large bowel obstructions, both to establish the cause and, in sigmoid volvulus or malignant obstruction, to deliver treatment through detorsion or stent placement.
The differential diagnosis includes ileus and pseudo-obstruction (which must be distinguished because management differs fundamentally), severe constipation and fecal impaction, mesenteric ischemia, acute pancreatitis, severe gastroparesis, and, in the appropriate clinical setting, ovarian pathology or other pelvic causes of distension and pain.
Important to Know
Bowel obstruction is managed as an emergency until proven otherwise, and initial care is largely the same regardless of cause. Care is coordinated by emergency physicians and general or colorectal surgeons, with gastroenterology, interventional radiology, and oncology involved depending on the underlying cause.
Initial management includes nothing by mouth, intravenous fluid resuscitation, correction of electrolyte abnormalities (particularly potassium, chloride, and the metabolic alkalosis that follows prolonged vomiting), and analgesia. Nasogastric tube decompression is used when there is significant vomiting or distension; it relieves symptoms, reduces the risk of aspiration, and allows monitoring of output. Urine output and hemodynamics are followed closely, since fluid losses into the obstructed bowel can be substantial and are easily underestimated.
The central early decision is whether the patient needs an operation now or can be observed. Features that mandate urgent surgery include peritonitis, evidence of strangulation or ischemia on examination or imaging, closed-loop obstruction, perforation, and hemodynamic instability. Obstruction caused by an incarcerated hernia generally requires prompt operative management.
For adhesive small bowel obstruction without these features, a trial of conservative management is standard and frequently successful. A substantial majority of partial adhesive obstructions resolve without surgery, typically within 24 to 72 hours. Water-soluble contrast studies help identify which patients will resolve, and current guidance generally supports proceeding to surgery if obstruction has not resolved within roughly three to five days, since prolonged observation beyond that point increases complications without improving the chance of resolution. Serial examination and repeat imaging guide the decision, and any deterioration prompts earlier operation.
Surgery for adhesive obstruction involves division of the responsible adhesions (adhesiolysis), with resection of any segment of bowel that is not viable. A laparoscopic approach is appropriate in selected patients and is associated with faster recovery, though open surgery remains necessary in many cases, particularly with dense adhesions or a hostile abdomen. Surgery for adhesions carries the inherent paradox of creating new adhesions, which is one reason a non-operative approach is preferred when it is safe.
Management of large bowel obstruction depends on the cause. Malignant obstruction may be treated with resection of the involved segment with primary anastomosis, resection with a stoma, or placement of an endoscopic self-expanding metal stent. Stenting is often used as a bridge to elective surgery—allowing decompression, medical optimization, and staging so that a subsequent operation can be performed under controlled conditions—or as definitive palliation in patients with advanced disease or who are not surgical candidates. Sigmoid volvulus is typically managed initially with endoscopic detorsion, which is usually successful but has a high recurrence rate, so elective sigmoid resection is generally recommended during the same admission in patients fit for surgery. Cecal volvulus generally requires surgery, as endoscopic reduction is far less reliable.
Ileus and acute colonic pseudo-obstruction are managed differently and non-operatively. Treatment addresses the underlying cause and precipitants: correcting electrolyte abnormalities, minimizing opioids and anticholinergic medications, treating infection, and encouraging mobilization. For acute colonic pseudo-obstruction that does not respond to supportive care, neostigmine is an effective pharmacologic option in appropriately monitored patients without contraindications, and colonoscopic decompression is an alternative. Marked cecal dilation raises the risk of perforation and warrants closer attention.
Malignant bowel obstruction in advanced cancer is a distinct situation requiring careful, goals-of-care-driven decision-making. Options range from surgery and stenting to venting gastrostomy and medical management with antiemetics, corticosteroids, and antisecretory agents such as octreotide. Palliative care involvement is valuable, and the least invasive approach that achieves comfort is often the right one.
Prevention is limited but not absent. Minimizing unnecessary abdominal surgery, using laparoscopic approaches where appropriate, and adhesion-reduction barriers in selected operations may reduce adhesive obstruction risk. Timely repair of symptomatic hernias prevents incarceration. Age-appropriate colorectal cancer screening reduces the likelihood of presenting with malignant obstruction as the first manifestation of colon cancer. Patients with a history of adhesive obstruction or Crohn’s strictures may benefit from dietary guidance about high-residue foods during symptomatic periods, though routine long-term restriction is generally not necessary.
Recurrence is common after adhesive obstruction, and patients should know the early warning signs so they seek care promptly rather than waiting.
Care during pregnancy is uncommon but important, since obstruction in pregnancy carries risk to both mother and fetus and diagnosis is often delayed because symptoms are attributed to pregnancy itself. Ultrasound and MRI are the preferred imaging modalities, and surgical management is not deferred when indicated.
Care is typically coordinated by surgical teams in the acute setting and by gastroenterology, oncology, or primary care thereafter depending on the cause. Imaging, laboratory, and clinical findings are interpreted alongside the patient’s symptoms, examination, surgical history, and broader clinical context rather than in isolation.
Patient education plays an important role. Understanding the cause of the obstruction, the rationale for a period of observation when one is offered, the warning signs that require immediate return to care, the recurrence risk after adhesive obstruction, and—where relevant—the reason a colonoscopy is recommended after a colonic obstruction all contribute to appropriate care.
Red flag symptoms include severe or constant abdominal pain (particularly a change from crampy to constant), abdominal distension with inability to pass gas or stool, persistent vomiting or vomiting that becomes feculent, high fever with chills, rapid heart rate or low blood pressure, generalized abdominal tenderness or rigidity, signs of sepsis (severe illness, confusion, cold clammy skin), inability to keep down fluids with signs of dehydration, and rapid clinical deterioration. These warrant immediate emergency evaluation, as they may indicate strangulation, bowel ischemia, perforation, peritonitis, or sepsis.