Definition of Intestinal Obstruction
Intestinal obstruction is defined as an interruption or impairment of the normal forward flow of intestinal contents, which can be caused by either mechanical blockage (intrinsic luminal obstruction or extrinsic compression) or functional failure of intestinal propulsion (adynamic ileus or pseudo-obstruction). 1
Mechanical vs. Functional Obstruction
The fundamental distinction in defining intestinal obstruction separates two pathophysiologic mechanisms:
Mechanical Obstruction
- Physical blockage preventing passage of intestinal contents through an anatomic narrowing or occlusion 2, 3
- Caused by intrinsic luminal obstruction (tumors, strictures, intussusception) or extrinsic compression (adhesions, hernias, masses) 1
- Radiologically characterized by a distinct transition point between dilated proximal bowel and normal or collapsed distal bowel 1
Functional Obstruction (Pseudo-obstruction)
- Failure of coordinated intestinal propulsion without mechanical blockage, resulting from lack of enteric propulsion 1
- Includes adynamic ileus and colonic pseudo-obstruction caused by drugs, trauma, postoperative states, or metabolic disturbances 1
- Presents with symptoms and signs of obstruction (distension, vomiting, pain) but no anatomic transition point on imaging 1
Clinical Characteristics
The clinical presentation that defines obstruction includes:
- Colicky abdominal pain that worsens after oral intake 4
- Nausea and vomiting (green/yellow vomit suggests proximal obstruction; feculent vomit suggests distal obstruction) 1
- Abdominal distension with tympany to percussion 2, 3
- Cessation of passage of flatus and stool (absolute constipation in complete obstruction) 4, 3
- High-pitched or hyperactive bowel sounds in mechanical obstruction 2, 3
Complete vs. Incomplete Obstruction
A critical definitional distinction:
- Complete obstruction: Regular vomiting or absolute constipation with distended abdomen, constituting a surgical emergency 4
- Incomplete obstruction: Intermittent symptoms with some passage of gas or stool, potentially manageable conservatively 4
Chronic Obstruction
Chronic intestinal obstruction is defined as persistent or recurrent mechanical obstruction lasting more than 6 months, typically from stricturing, adhesions, fibrosis, or mass effect 4. This must be distinguished from chronic intestinal pseudo-obstruction (CIPO), which represents chronic dysmotility rather than true mechanical blockage 4.
Pathophysiologic Consequences
The definition encompasses the downstream effects of obstruction:
- Fluid and gas accumulation proximal to the obstruction site 5
- Bowel wall edema and increased secretion into the lumen 1
- Risk of progression to mucosal ischemia, necrosis, and perforation if untreated 2, 5
- Strangulation when vascular compromise occurs, representing a surgical emergency 5, 3
Common Pitfall
The most critical diagnostic error is failing to distinguish mechanical obstruction from functional pseudo-obstruction, as this fundamentally changes management from potential surgical intervention to conservative medical therapy 1. A premature diagnosis of dysmotility when localized adhesive obstruction exists can delay necessary surgical treatment 1.