Evidence‑Based Diagnosis and Management of Bowel Obstruction

Etiology

Adhesions are the predominant cause of small‑bowel obstruction, responsible for 55 %–75 % of cases, with postoperative adhesions being the primary source【1】【2】.
Additional small‑bowel obstruction etiologies include inflammatory disease, intussusception, volvulus, gallstone ileus, and bezoars【1】【2】.

Small‑bowel obstruction typically presents with intermittent, crampy central abdominal pain【1】【2】.
Auscultation often reveals high‑pitched or absent bowel sounds in small‑bowel obstruction【1】【2】.
Warning signs of ischemia/strangulation for any obstruction (fever, hypotension, peritonitis, elevated lactate, leukocytosis with left shift) do not exclude ischemia when normal【2】【3】.

Plain abdominal radiography detects small‑bowel obstruction with a sensitivity of 60 %–74 %, but is insufficient to rule out obstruction or to determine surgical need【3】【1】【3】.
CT of the abdomen and pelvis is the gold‑standard imaging modality for both small‑ and large‑bowel obstruction (American College of Radiology).
- Small‑bowel obstruction on CT shows dilated loops > 3 cm with air‑fluid levels【1】【2】.
- A transition point with collapsed distal bowel confirms the obstruction level【1】.
- In high‑grade obstruction, oral contrast is unnecessary because intraluminal fluid provides adequate contrast【1】.
- Overall CT diagnostic accuracy exceeds 90 % for identifying obstruction and its cause【1】【2】.
CT signs of bowel ischemia (altered wall enhancement, wall thickening, mesenteric edema, ascites, pneumatosis, mesenteric venous gas) are critical for urgent decision‑making【1】.

Conservative therapy (nil per os, intravenous fluids, nasogastric decompression, analgesia) is appropriate for most low‑grade small‑bowel obstructions【1】【2】.
A water‑soluble contrast challenge (≈100 mL hyperosmolar contrast, radiographs at 8 h and 24 h) predicts need for surgery; if contrast reaches the colon by 24 h, operative intervention is rarely required【2】【3】.
Immediate surgery is indicated for any obstruction with signs of ischemia, complete or closed‑loop obstruction, volvulus, or failure of conservative measures after 3–5 days【1】【2】.
Do not delay CT imaging when obstruction is suspected; plain films alone are inadequate【1】【3】.
Normal lactate and white‑cell count do not rule out ischemia; clinical judgment and CT findings must guide management【2】【3】.

When bowel ischemia develops, mortality can reach 25 %, underscoring the importance of early recognition and timely intervention【1】【2】.

Note: Water‑soluble contrast is *not recommended* for large‑bowel obstruction management【3】.

Adhesions are the single most common cause of small bowel obstruction, representing 55-75% of all cases, with post-surgical adhesions being the predominant type 4, 5, 6, 7
A history of prior abdominal surgery has 85% sensitivity and 78% specificity for predicting adhesive small bowel obstruction 4
Hernias account for 15-25% of small bowel obstructions 4
Malignancies cause 5-10% of small bowel obstructions, with both primary small bowel tumors and metastatic disease being responsible 4, 5, 6, 7
Carcinomatosis peritoneal represents a less frequent but important cause of small bowel obstruction 4, 8
Endometriosis can cause small bowel obstruction, particularly in women of reproductive age 4, 8
Inflammatory bowel disease stenosis, particularly Crohn's disease, causes obstruction through stricture formation 4, 8

Colorectal cancer is the leading cause of large bowel obstruction, responsible for approximately 60% of cases, and requires urgent evaluation to exclude malignancy 4, 8
Volvulus accounts for 15-20% of large bowel obstructions, with sigmoid volvulus being the most common type 4, 8
Diverticular disease causes approximately 10% of large bowel obstructions, with previous diverticulitis episodes suggesting diverticular stenosis 4, 8
Inflammatory bowel disease can cause colonic stenosis and obstruction 4, 8

Adynamic ileus and pseudo-obstruction are caused by lack of enteric propulsion rather than mechanical blockage and must be distinguished from true mechanical obstruction 4, 9
Drugs that affect peristalsis, particularly opioids, can cause functional obstruction 4, 8
Trauma and the postoperative period can lead to functional obstruction 4, 8
Metabolic disturbances, including electrolyte abnormalities, can cause functional obstruction 4, 8
Bevacizumab causes ulceration, fistulation, or perforation in 0.9% of patients within 1 year 10
Tyrosine kinase inhibitors are associated with bowel perforation 10
Radiotherapy-induced fibrosis can cause chronic strictures, particularly in the sigmoid colon after pelvic radiation 10