The MRI features of **small vessel disease (SVD)** primarily reflect the damage caused by chronic dysfunction of the brain’s small blood vessels, which affects the white matter and deep brain structures. These features are diverse but can be grouped into several key imaging findings that help in diagnosing and understanding the extent and progression of the disease.
**White matter hyperintensities (WMHs)** are the hallmark MRI feature of small vessel disease. On MRI scans, particularly on T2-weighted and FLAIR sequences, these appear as areas of increased signal intensity in the white matter. They represent regions of demyelination, gliosis, and axonal loss caused by chronic ischemia due to small vessel pathology. These lesions are typically bilateral and patchy or diffuse, often found around the ventricles (periventricular) and in the deep white matter. The severity of WMHs can be graded using scales such as the Fazekas scale, which helps quantify the burden of white matter changes and correlates with clinical symptoms like cognitive decline.
**Lacunar infarcts** are another important feature seen in small vessel disease. These are small, deep infarcts usually less than 15 mm in diameter, resulting from occlusion of a single small penetrating artery. On MRI, lacunes appear as small cavities or fluid-filled spaces that are hypointense on T1-weighted images and hyperintense on T2-weighted images, often surrounded by a rim of gliosis. They are typically located in the basal ganglia, thalamus, internal capsule, or brainstem. Lacunes reflect previous small vessel strokes and contribute to neurological deficits and cognitive impairment.
**Enlarged perivascular spaces (EPVS)**, also known as Virchow-Robin spaces, are fluid-filled spaces surrounding small blood vessels as they penetrate the brain. On MRI, EPVS appear as small, round or linear hyperintensities on T2-weighted images, usually less than 3 mm in diameter. They are most commonly seen in the basal ganglia and centrum semiovale. While EPVS can be a normal finding, an increased number and size are associated with small vessel disease and may indicate impaired interstitial fluid drainage or vessel wall changes.
**Cerebral microbleeds (CMBs)** are small, chronic blood deposits resulting from leakage of blood through fragile small vessels. On MRI, they are best visualized using susceptibility-weighted imaging (SWI) or gradient-recalled echo (GRE) sequences as small, round hypointense (dark) lesions. Microbleeds are typically located in deep brain regions such as the basal ganglia, thalamus, brainstem, and cerebellum in hypertensive small vessel disease, or in lobar regions in cerebral amyloid angiopathy, a subtype of small vessel disease. Their presence indicates microvascular fragility and is linked to an increased risk of hemorrhagic stroke.
**Brain atrophy** is often seen in patients with advanced small vessel disease. This manifests as a generalized or focal loss of brain volume, particularly affecting the white matter and subcortical structures. On MRI, brain atrophy is evident as widened sulci, enlarged ventricles, and reduced volume of the cerebral cortex and deep gray matter nuclei. Atrophy reflects the cumulative effect of chronic ischemia, infarcts, and tissue loss.
**Diffusion tensor imaging (DTI)**, an advanced MRI technique, can detect microstructural changes in the white matter that are not visible on conventional MRI. DTI measures the integrity of white matter tracts by assessing water diffusion properties. In small vessel disease, DTI shows reduced fractional anisotropy and increased mean diffusivity in affected regions, indicating disrupted white matter microstructure. These changes correlate with cognitive dysfunction and disease severity.
**Cerebrovascular reactivity (CVR)** assessed by functional MRI techniques, such as blood-oxyge
