Vascular MRI

MRI in the Diagnosis of Vascular Dementia

Vascular dementia (vascular dementia, VaD) is a heterogeneous group of disorders for which neuroimaging is crucial. Conventionally, three key lesion patterns are distinguished on MRI:

1. Large-vessel disease (large-vessel disease, LVD). Develops as a result of single or multiple cortico-subcortical lesions, as well as infarctions in borderzone areas (borderzone infarcts). Strategically important areas are affected: the hippocampus and thalamocortical networks. The most severe cognitive impairment develops when the dominant hemisphere is involved.
2. Small-vessel disease (small-vessel disease, SVD). This is the most frequent form, also known as leukoaraiosis (leukoaraiosis). It manifests as extensive (more than 25%) involvement of the white matter in the frontal and parietal lobes, as well as multiple lacunes in the basal ganglia and centrum semiovale (centrum semiovale). In SVD, the temporal lobes and U-fibers remain intact.
3. Bilateral thalamic infarctions. Small lesions in the medial regions of the thalamus.

Various sequences are used to evaluate lesions. FLAIR is the optimal choice for small-vessel pathologies, as it clearly separates bright areas of leukoaraiosis from dark lacunes. Diffusion-weighted imaging (DWI) brightly highlights acute lacunar infarcts. T2-weighted imaging better displays problems in the thalamus, while T1-weighted imaging is useful for identifying areas of severe destruction (they appear hypointense, and their severity correlates with clinical presentation).

Genetic Small-Vessel Disorders

Sometimes small-vessel pathologies are genetically determined. MRI allows them to be suspected based on specific patterns:

• CADASIL (notch-3 gene mutation). Unlike sporadic leukoaraiosis, at the preclinical stage, white matter in the temporal pole is affected here. Later, the U-fibers of the convexital surface become involved, and lacunes and microbleeds appear.
• Fabry disease (Fabry disease). Causes about 1% of strokes in young men. A specific radiological marker is hyperintensity of the thalamic pulvinar (pulvinar) on T1-weighted images and hypointensity on T2*-weighted images (the result of calcification).
• Cerebral amyloid angiopathy (CAA). Associated with $\beta$-amyloid deposition in arterial walls. MRI reveals lobar (lobar) hemorrhages and infarctions. In later stages, microbleeds (microbleeds) appear. These microlesions are invisible on standard sequences; they can only be detected on T2* gradient-echo (GRE) or susceptibility-weighted imaging (SWI).

Evaluation of Mediastinal Vessels and Bone Complications

MRI has significant advantages in the differential diagnosis of mediastinal space-occupying lesions (e.g., distinguishing a thymic cyst from a solid tumor) and assessing their relationship with large intrathoracic vessels. The main advantage of the method is the ability to differentiate solid tissue from vessels without contrast administration. Rapidly flowing blood causes a "signal void" (signal void) effect on spin-echo sequences (spin-echo sequences), making vessels appear dark. A disadvantage of MRI compared to CT is poor visualization of calcifications.

Vascular complications can also occur peripherally in bone tumors. For example, in hereditary multiple exostoses (diaphyseal aclasis), trauma to the popliteal artery by an osteochondroma can lead to the formation of a pseudoaneurysm.

Embryology of the Cerebral Vasculature

An understanding of embryogenesis is important for radiological anatomy. The hemispheres develop from telencephalic vesicles. A vascular fissure (choroid fissure) forms in the roof of the future third ventricle, from which the choroid plexus (choroid plexus) develops. In the embryo, it is proportionally much larger than in the adult. Blood drainage from the plexus occurs via the median vein of the prosencephalon—the precursor of the vein of Galen (vein of Galen). During development, the internal carotid artery divides: its anterior branch forms the anterior cerebral artery, and its posterior branch forms the posterior communicating artery.

Class and exam questions

What else to study on this topic

• MR microscopy and visualization of cerebral cortex thickness on 7T systems.
• The role of 3D CT reconstructions in the evaluation of pseudoaneurysms in diaphyseal aclasis.
• Differential diagnosis of benign cysts and cystic neoplasms of the mediastinum on MRI.
• The specific "pulvinar sign" on T1- and T2*-weighted imaging in Fabry disease.

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.