Microembolus

A microembolus is a tiny particulate that occludes small vessels, typically arterioles or capillaries, and can detach from a proximal source to travel within the circulation. The term encompasses a variety of compositions, most commonly cholesterol crystals from atherosclerotic plaques, platelet aggregates, fat droplets, air bubbles, or, rarely, tumor cells.

Common sources include atherosclerotic disease, atrial fibrillation, endocarditis, prosthetic heart valves, trauma, and medical procedures such as angiography where devices can dislodge material. The resulting obstruction causes focal ischemia and microinfarcts in the affected tissue; distal migration can spread injury to other small vessels. In some contexts, microemboli contribute to reperfusion injury or microhemorrhage.

Clinical presentation depends on the organs involved. Cerebral microemboli may produce transient neurologic deficits or contribute to silent brain infarcts detected on imaging. Retinal microemboli can manifest as transient visual disturbances or be visible as cholesterol emboli (Hollenhorst plaques) on fundoscopic exam. Pulmonary microemboli are often clinically silent when small but can contribute to ventilation–perfusion abnormalities in larger events. Systemic microembolization can affect kidneys, limbs, or other organs.

Diagnosis relies on risk factors and targeted testing. Magnetic resonance imaging may reveal multiple small diffusion-restricted lesions consistent with microinfarcts. Transcranial Doppler can detect microembolic signals. Echocardiography and vascular imaging help identify cardiac or arterial sources. Fundoscopic examination can detect retinal emboli.

Management focuses on preventing further embolization and treating the underlying cause. Antiplatelet therapy is common for noncardioembolic etiologies; anticoagulation is used for cardioembolic sources such as atrial fibrillation. Risk factor modification, statin therapy, and careful procedural techniques to minimize distal embolization are important. The presence of microemboli indicates ongoing embolic risk and may be associated with higher chances of future stroke or cognitive decline. See also embolism, cholesterol embolization, fat embolism, air embolism.