16 Perivascular spaces and lacunar infarcts may appear similar and be difficult to differentiate on imaging. There are some features that can aid in this differentiation (Table 16.1). Lacunar infarcts are defined as small subcortical and deep infarcts (<15 mm in diameter) due to occlusion of a single deep penetrating artery and may be asymptomatic or present with specific lacunar or other neurological symptoms. They occur most frequently in the basal ganglia and internal capsule, thalamus, corona radiata, and brain stem. Their imaging appearance varies with age. Acute lacunar infarcts are often undetectable on computed tomography (CT), but may appear as hypodensities. Magnetic resonance imaging (MRI) is much more sensitive than CT, with lacunar infarcts appearing isointense to mildly hypointense on T1-weighted MR images (T1WI) and hyperintense on T2-weighted MR images (T2WI) or fluid-attenuated inversion recovery (FLAIR) with restricted diffusion on diffusion weighted imaging (DWI) and apparent diffusion coefficient (ADC maps). A chronic lacunar infarct may be difficult to distinguish from a perivascular space. It may be cystic with CSF density and intensity on CT and MRI, respectively. It may be isointense to mildly hypointense on T1WI if not cystic. If the lacuna is close to the ventricular system, it may cause focal ex-vacuo dilatation of the ventricle.
Perivascular Spaces versus Lacunar Infarcts
Lacunar Infarcts
| Perivascular Space | Lacunar Infarct | |
|---|---|---|
| Location | Basal ganglia, thalamus, white matter near vertex, subinsular, although may be seen anywhere in the brain | Basal ganglia, internal capsule, thalamus, corona radiata or pons |
| MRI | CSF intensity on all imaging sequences (usually) |
