What is a Lacunar Infarct?
A lacunar infarct is a small subcortical stroke measuring less than 1.5 cm in diameter on CT or MRI, typically located in deep brain structures (basal ganglia, brainstem, or deep white matter—but not the cerebral cortex), resulting from occlusion of a single penetrating artery. 1
Clinical Definition and Imaging Characteristics
Lacunar stroke is defined by the American Heart Association/American Stroke Association as either:
- A lacunar syndrome presentation with normal CT/MRI, OR
- A subcortical stroke measuring <1.5 cm in diameter on CT or MRI 1
The majority (though not all) of lacunar strokes are caused by small vessel disease 1. These infarcts result from occlusion of small penetrating arteries with diameters ranging between 100-400 micrometers 2.
Anatomical Distribution
The term "lacunar infarct" should be specifically reserved for cystic lesions smaller than 1 cm located in:
- Basal ganglia
- Brainstem
- Deep white matter
- Explicitly NOT the cerebral cortex 1
This anatomical specificity is critical for accurate diagnosis, as cortical involvement suggests a different stroke mechanism 1.
Underlying Pathophysiology
The primary arterial pathologies causing lacunar infarcts include 2:
- Lipohyalinosis (most common small vessel pathology)
- Microatheroma
- Fibrinoid necrosis
- Charcot-Bouchard aneurysm formation
Less common causes include cerebral amyloid angiopathy and CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) 2, 1.
Clinical Presentation
Patients typically present with one of five classic lacunar syndromes 3, 2:
- Pure motor hemiparesis (most common)
- Pure sensory syndrome
- Sensorimotor stroke
- Ataxic hemiparesis
- Dysarthria-clumsy hand syndrome
The lacunar syndrome has excellent diagnostic accuracy, with 95% sensitivity and 93% specificity for identifying lacunar infarction 4.
Epidemiological Significance
Lacunar strokes account for approximately 77% of all ischemic strokes (which themselves comprise 88% of all strokes), making them the predominant ischemic stroke subtype 1. They represent about one-quarter of all cerebral infarctions 3, 5.
Risk Factors
Hypertension and diabetes mellitus are the major risk factors for lacunar stroke 3. Importantly, cardiac sources of embolism are significantly less frequent in lacunar infarction (odds ratio 0.32) compared to cortical strokes, and significant carotid stenosis is also less common (odds ratio 0.35) 4.
Prognosis and Long-Term Implications
Despite initially mild symptoms, lacunar infarcts have a paradoxical clinical course 3, 5:
- Short-term: Favorable prognosis with low early mortality and reduced functional disability at hospital discharge 3
- Long-term: Increased risk of death, stroke recurrence, dementia, and cognitive decline 3, 5
Approximately 15-20% of patients experience early neurological deterioration (END), which is consistently associated with poor functional outcomes 6. The pooled incidence of END is 23.54% when defined by various NIHSS decrease thresholds 6.
Evolution on Imaging
Long-term imaging studies reveal that 7:
- 41% of lacunar infarcts show complete cavitation at 1-year follow-up
- 51% show partial cavitation
- 53% develop new white matter hyperintensities adjacent to the index infarct (either superior "caps" or inferior "tracks"), reflecting ongoing small vessel disease progression 7
Critical Clinical Pitfall
Lacunar infarction should be regarded as a potentially severe condition rather than a benign disorder, despite favorable initial presentation 3, 5. The asymptomatic progression of small vessel disease is a typical feature, necessitating rigorous long-term management and follow-up 3.
While embolic causes are rare, they can occur—case reports document pure motor hemiplegia from emboli during cardiac angiography, proving that emboli can occasionally cause lacunar syndromes 8. However, small vessel disease remains the predominant mechanism, supported by the significantly lower frequency of cardiac and carotid embolic sources in lacunar versus cortical infarcts 4.