What do MRI and CT images of a lacunar infarct look like?

Imaging Characteristics of Lacunar Infarcts on MRI and CT

MRI is superior to CT for detecting lacunar infarcts, with T2-weighted sequences being the most sensitive imaging modality for identifying these small, deep cerebral lesions. 1

MRI Appearance of Lacunar Infarcts

Signal Characteristics

• T1-weighted images: Lacunae appear as focal areas of decreased signal intensity (hypointense) 1
• T2-weighted images: Lacunae appear as focal areas of increased signal intensity (hyperintense) 1
• T2-weighted sequences detect significantly more lacunar infarcts than T1-weighted or mixed T1/T2-weighted images 1

Timing-Based Appearance

• Acute lacunar infarcts (within 1 week of symptom onset):

  • Visible only on T2-weighted images 1
  • Show hyperintensity on diffusion-weighted imaging (DWI) 2
  • No demarcation on T1-weighted scans 3
  • May show gadolinium enhancement 3, 4

• Chronic lacunar infarcts (more than 1 week):

  • Visible on both T1- and T2-weighted images 1
  • Approximately 61-70% develop cavitation on follow-up imaging 2
  • One-third do not develop a cavity and remain as areas of gliosis 2

Size and Location

• Lacunar infarcts are ≤25 mm in diameter (typically <20 mm) 2, 5
• Located in the distribution of penetrating arteries: basal ganglia, internal capsule, thalamus, pons, and deep white matter 1, 5
• Acute DWI significantly overestimates final infarct size—mean baseline DWI size of 13.5 mm reduces to 8.2 mm on follow-up 2

Gadolinium Enhancement

• Gadolinium-DTPA enhancement on MRI is excellent for identifying recent lacunar infarcts in patients with multiple small infarctions 4
• Enhancement helps distinguish recent infarcts from old lesions definitively 4

CT Appearance of Lacunar Infarcts

Detection Limitations

• CT is significantly less sensitive than MRI for detecting lacunar infarcts 1, 3
• Early CT (within 48 hours) shows lacunar infarcts in only 50-53% of cases with clinical lacunar syndromes 3
• No lesions are identified on CT that are not also detected by MRI 1

CT Characteristics

• Appear as small, hypodense (dark) lesions in deep brain structures 1
• Located in basal ganglia, internal capsule, thalamus, or pons 5
• Contrast enhancement on CT is weak and inconsistent—enhances recent lesions in only 44% of patients 4
• Follow-up CT shows cavity formation in 70% of cases 2

Clinical Imaging Recommendations

Initial Imaging Selection

• CT head without IV contrast is usually appropriate for initial evaluation to exclude hemorrhage 6, 7
• MRI head without IV contrast is usually appropriate and more sensitive for detecting acute lacunar infarcts 6, 7
• For acute stroke <6 hours: CT head without contrast rated 9/9 (highest appropriateness) for rapid hemorrhage exclusion 7
• For acute stroke >6 hours: MRI head without contrast rated 8/9 for superior infarct detection 7

Key Imaging Pitfalls

• Clinical lacunar syndromes have 94% positive predictive value for MRI-confirmed lacunar infarcts 3
• Periventricular white matter lesions predict cavity formation on follow-up imaging 2
• Small subcortical infarcts from large-vessel disease can mimic lacunar infarcts but show fewer basal ganglia hyperintensities and less perivascular space enlargement 8
• Progressive stroke is more common in lacunar-like infarcts from large-vessel disease than true lacunar infarcts 8