In medical terms, occlusion means a blockage or closure of a passage in the body. Most often it refers to a blood vessel that has become partially or completely blocked, cutting off flow to the tissue beyond it. But the term also applies to blocked intestines, airways, and even the way your upper and lower teeth fit together. The specific meaning depends entirely on context, and each type of occlusion carries different risks and urgency.
Vascular Occlusion: Blocked Blood Vessels
The most common medical use of “occlusion” describes a blood vessel that has narrowed or closed off. This can happen in arteries (which carry oxygen-rich blood away from the heart) or veins (which return blood back). The blockage starves downstream tissue of oxygen, and the consequences depend on which vessel is affected and how quickly the blockage forms.
There are three main ways a vessel becomes occluded. A thrombus is a clot that forms in place, typically where fatty plaque has built up along the vessel wall. An embolus is a clot or debris that forms somewhere else in the body, breaks loose, and travels until it lodges in a smaller vessel downstream. The third cause is mechanical compression, where a tumor, hernia, or external force physically squeezes a vessel shut.
Arterial and venous clots actually form through somewhat different mechanisms. Arterial clots tend to involve platelet activation, where sticky cell fragments clump together at a site of plaque buildup. Venous clots rely more on the clotting cascade, the chain reaction of proteins in your blood that produces fibrin strands. In practice, though, both systems overlap. Atherosclerosis (plaque buildup in arteries) triggers enough clotting activity throughout the body that it can even promote clot formation in veins.
Where Vascular Occlusion Strikes
Heart
When a coronary artery becomes occluded, the heart muscle it feeds begins to die. This is a heart attack (myocardial infarction). The severity depends on whether the blockage is total or partial, whether nearby vessels can reroute some blood flow, and how quickly the artery is reopened. A total occlusion with no backup circulation means the affected heart muscle faces irreversible damage without rapid treatment.
Brain
An occluded artery in the brain causes an ischemic stroke. Imaging with CT angiography can pinpoint the blocked vessel, and adding perfusion imaging (which maps blood flow changes in brain tissue) makes it easier to identify both the blockage site and the area of brain at risk. Speed is critical: the longer brain tissue goes without blood, the more cells die.
Eyes
Central retinal artery occlusion blocks blood flow to the retina, causing sudden, painless vision loss in one eye. The prognosis is poor. In a study of 794 patients, about 90% presented with vision of 20/200 or worse, which is the threshold for legal blindness. Even among those who reached a hospital within four and a half hours, 93% had vision that severe, and roughly 93% of those never improved beyond it. There was no significant difference in outcomes between patients who arrived before versus after that time window.
Legs and Arms
Peripheral artery disease develops when arteries in the limbs gradually narrow. The progression follows a recognizable pattern. It starts with no symptoms at all, then progresses to pain during walking (claudication), then pain at rest, and finally tissue death in the foot or leg. Six hours has long been considered the danger threshold for a sudden arterial blockage in a limb, but research on lower extremity injuries shows that limb salvage is best when blood flow is restored within one hour. The amputation rate was 6% for repairs done within 60 minutes, compared to nearly 12% for those done between one and three hours later.
Intestinal Occlusion
When doctors describe an intestinal occlusion, they mean a bowel obstruction, something physically preventing food and fluid from passing through. In adults, the three most common causes are adhesions (bands of scar tissue from prior abdominal surgery), hernias, and colon cancer. Other causes include Crohn’s disease, diverticulitis, a twisted colon (volvulus), and impacted stool. In children, the most common cause is intussusception, where one section of intestine telescopes into the section next to it.
There is also a functional version called pseudo-obstruction or paralytic ileus. In this case nothing is physically blocking the intestine, but the muscles and nerves that move food along have stopped working properly. This can happen after abdominal surgery, during infections, or as a side effect of certain medications like opioids and some antidepressants. Parkinson’s disease and other nerve disorders can also trigger it.
Dental Occlusion: How Your Teeth Meet
In dentistry, occlusion simply refers to how your upper and lower teeth come together when you close your mouth. An ideal bite has 1 to 2 millimeters of horizontal overlap (overjet) and 1 to 2 millimeters of vertical overlap (overbite), with minimal crowding and smooth side-to-side movement.
Malocclusion means the bite is off. The standard classification system, developed by Edward Angle and still used today, divides bite alignment into three classes based on how the upper and lower first molars line up. Class I is a normal molar relationship (though the teeth themselves may still be crooked). Class II means the upper jaw sits too far forward relative to the lower jaw, the pattern many people recognize as an overbite. Class III is the reverse, where the lower jaw protrudes ahead of the upper. Signs of malocclusion go beyond cosmetics: misaligned bites can cause speech problems, difficulty chewing, mouth breathing, and changes in facial structure over time.
How Occlusions Are Detected
For vascular occlusions, doctors rely on imaging. Doppler ultrasound is often the first step, especially for blockages in the legs or neck. It uses sound waves to measure blood flow speed and direction, making it quick and noninvasive. CT angiography provides detailed images of blood vessels and is the go-to tool for stroke evaluation, since it can identify which artery is blocked and how much brain tissue is at risk. MR angiography offers similar detail without radiation and is useful for planned evaluations rather than emergencies.
For intestinal occlusions, X-rays and CT scans of the abdomen can reveal dilated loops of bowel, air-fluid levels, and the point where the blockage starts. Dental occlusion is assessed through physical examination, dental impressions, and sometimes X-rays to evaluate jaw alignment.
Treatment Depends on the Location
Vascular occlusions in arteries are typically treated by reopening the vessel. Angioplasty threads a tiny balloon to the blockage site and inflates it to widen the passage. A stent, a small wire mesh tube, can then be placed to hold the vessel open. For blockages in the iliac artery (in the pelvis), stenting achieves a 98% technical success rate compared to 84% for angioplasty alone, with fewer complications. When less invasive options fail, bypass surgery reroutes blood around the blockage. Bypass has excellent long-term patency rates but comes with greater surgical risk.
Intestinal occlusions often require hospital care with intravenous fluids and bowel rest. Partial blockages sometimes resolve on their own, while complete blockages or those caused by hernias or tumors typically need surgery. Dental malocclusion is treated with orthodontics, ranging from braces to jaw surgery depending on the severity and class of misalignment.