A microhemorrhage is a microscopic bleed within the brain’s tissue that does not produce immediate symptoms. Because individuals cannot feel them, they are most often discovered incidentally during brain imaging scans. These tiny bleeds result from the rupture of small blood vessels like arterioles and capillaries. Their presence is a sign of underlying damage to the brain’s smallest vessels.
Underlying Causes and Risk Factors
Cerebral microhemorrhages stem from conditions that weaken the walls of the brain’s smallest blood vessels, with two of the most common causes related to aging and chronic disease. Cerebral amyloid angiopathy (CAA) is a frequent cause, particularly in older adults. CAA involves the buildup of an amyloid protein in the walls of cerebral arteries, making them brittle and prone to rupture. This condition is often found in individuals with Alzheimer’s disease.
Chronic high blood pressure, or hypertensive arteriopathy, is another primary driver of microhemorrhages. Persistently elevated blood pressure stresses the walls of small, deep-penetrating arterioles in the brain. Over time, this pressure causes structural damage that can lead to ruptures.
Traumatic brain injury (TBI) can cause these tiny bleeds, as shearing forces from rapid head acceleration or deceleration can tear small blood vessels. Other less frequent factors include certain genetic disorders like CADASIL, side effects from radiation therapy to the brain, and the use of anticoagulant medications.
Detection and Diagnosis
Cerebral microhemorrhages are too small to be seen on standard computed tomography (CT) scans. Their detection requires sensitive Magnetic Resonance Imaging (MRI) technology. Specific MRI sequences are necessary to make them visible, as these are designed to be highly sensitive to the magnetic properties of iron.
When a small blood vessel ruptures, red blood cells escape into the surrounding brain tissue. As these cells break down, they leave behind tiny deposits of an iron-storage protein called hemosiderin. This residual iron disrupts the local magnetic field, which is then detected by specialized MRI sequences like Gradient-Recalled Echo (GRE) and Susceptibility-Weighted Imaging (SWI).
On these MRI scans, the iron deposits from microhemorrhages appear as small, dark, circular spots, defined as less than 10 millimeters in diameter. The location and number of these spots provide clues about the underlying cause. For example, bleeds in the outer (lobar) regions of the brain suggest cerebral amyloid angiopathy, while those in deep brain areas are more indicative of long-standing hypertension.
Associated Health Conditions
Microhemorrhages are not a disease but an indicator of increased risk for other neurological problems. They serve as a marker for underlying small vessel disease in the brain. The number and location of these bleeds often correlate with the risk level for developing more significant health issues.
A strong association exists between cerebral microhemorrhages and a greater risk for cognitive decline and dementia. A higher number of these bleeds is linked to poorer performance on cognitive tests and an increased likelihood of developing vascular dementia or Alzheimer’s disease. They are thought to contribute to the progressive impairment of brain function by damaging neuronal pathways.
Their presence also signals an elevated risk for future strokes, both ischemic (blockage) and hemorrhagic (larger bleed). While not a stroke itself, a microhemorrhage represents vascular fragility and a predisposition to more substantial cerebrovascular events. In individuals with a history of TBI, these bleeds are also studied for their connection to the long-term development of chronic traumatic encephalopathy (CTE).
Managing Underlying Conditions
There is no direct treatment to repair or remove existing microhemorrhages. Medical management focuses on addressing the root causes to prevent new ones from forming and to reduce the risk of associated complications. The goal is to mitigate factors that damage the small blood vessels.
The most significant modifiable risk factor is high blood pressure. Strict control of hypertension is a central management strategy, especially for bleeds located in deep brain structures. Maintaining a healthy blood pressure through medication and lifestyle changes helps protect the brain’s vasculature.
Lifestyle modifications play a large part in risk reduction. A heart-healthy diet, regular physical exercise, and stopping smoking can positively impact vascular health. For patients taking blood-thinning medications, the discovery of numerous microhemorrhages may require a physician to reassess the balance between the medication’s benefits and the increased bleeding risk.