What causes microhemorrhages in the basal ganglia, particularly in elderly patients with a history of hypertension, vascular disease, or dementia?

Microhemorrhages in the Basal Ganglia: Etiology

Microhemorrhages in the basal ganglia are primarily caused by hypertensive small vessel angiopathy (arteriolosclerosis), which damages the small penetrating arteries supplying these deep brain structures. 1

Primary Etiologic Mechanism

Hypertensive vasculopathy is the dominant cause of microhemorrhages specifically in deep locations including the basal ganglia, thalami, and brainstem. 1 This differs fundamentally from lobar microhemorrhages, which are typically caused by cerebral amyloid angiopathy (CAA). 1

Pathophysiology of Hypertensive Damage

• Chronic hypertension causes arteriolosclerosis—concentric fibrotic thickening of small penetrating arteries (up to 300 microns diameter) that supply the basal ganglia. 2

• This arterial pathology leads to vessel wall weakening and eventual micro-leakage of blood into adjacent brain tissue, forming focal hemosiderin deposits. 1

• The damaged vessels show lipohyalinosis (the lesions Fisher described adjacent to lacunes) in more severe cases. 2

Associated Risk Factors and Conditions

Vascular Risk Factors

• Age is a fundamental risk factor, with prevalence increasing substantially in elderly populations. 1

• Arterial hypertension shows the strongest association with deep/basal ganglia microhemorrhages. 1

• Cardiovascular risk factors collectively increase prevalence from ~6% in healthy elderly to 50-80% in those with cerebrovascular disease. 1

Co-occurring Pathology

• Deep microhemorrhages are strongly associated with white matter hyperintensities and lacunar infarcts, reflecting shared small vessel disease pathology. 1

• Patients with basal ganglia microhemorrhages typically show progression of white matter lesions over time. 1

Location-Specific Etiology

The anatomic location of microhemorrhages indicates their underlying cause: 1

• Deep locations (basal ganglia, thalami, brainstem) → hypertensive vasculopathy
• Lobar locations (cortical-subcortical) → cerebral amyloid angiopathy
• Mixed patterns suggest combined pathology

This location-based distinction is critical because it has different implications for hemorrhage risk and management strategies. 1

Less Common Causes

Microembolic Events

• Cardiac bypass procedures can cause microemboli leading to microhemorrhages in various locations including basal ganglia. 1

Vascular Malformations

• Arteriovenous malformations, dural arteriovenous fistulas, and cavernous malformations in the basal ganglia region can produce microhemorrhages. 3

• Moyamoya disease causing chronic ischemia may lead to microhemorrhages. 3

Clinical Significance

Cognitive Impact

• Multiple microhemorrhages in basal ganglia correlate with worse performance on psychomotor speed and executive functioning tests. 4

• The presence of microhemorrhages is associated with increased risk of developing vascular dementia, though causality versus marker status remains uncertain. 1, 4

Hemorrhage Risk

• Greater number of baseline microhemorrhages confers greater risk of subsequent incident microhemorrhages. 1

• Unlike lobar microhemorrhages from CAA, deep microhemorrhages do not specifically predict lobar macrohemorrhage risk. 1

Important Diagnostic Pitfalls

When interpreting imaging for basal ganglia microhemorrhages, be aware of: 1

• Physiological mineralization in basal ganglia can mimic microhemorrhages on T2* sequences
• Vessel flow voids appearing as punctate hypointensities when vessels transect the imaging plane perpendicularly
• Bulk susceptibility artifacts near skull base that can obscure or mimic lesions
• Motion artifacts creating false positives

These interpretive challenges mean that side-by-side comparison with follow-up scans often provides more diagnostic certainty than single examinations. 1