Brain magnetic resonance angiography

Capabilities of MRI in the study of cerebral vessels

Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) are widely used for the non-invasive assessment of the arterial bed. Unlike routine angiography, MRI provides information not only on vessel lumen geometry, but also on the state of the surrounding tissues and the vascular wall itself.

Specialized protocols are used for detailed diagnostics:

• Diffusion-weighted imaging (DWI): indispensable for detecting small acute infarcts, for example, in the deep territory of the middle cerebral artery (MCA).
• Black-blood imaging sequences (black-blood imaging): contrast-enhanced T1-weighted images where the signal from flowing blood is suppressed. This allows targeted visualization of the vascular wall (vessel wall imaging) and detection of contrast enhancement against a dark lumen.

Primary angiitis of the central nervous system (PACNS)

This is a rare and severe idiopathic disease causing multifocal inflammation of small CNS arteries. Clinically, it may manifest as episodes of minor strokes and transient ischemic attacks (TIAs) across multiple vascular territories.

Neuroimaging presentation in PACNS:

• Brain MRI abnormalities are present in more than 90% of patients, although findings are often non-specific.
• The subcortical white matter is predominantly affected, followed by the deep grey and white matter, as well as the cortex.
• Focal white matter lesions can be misidentified as multiple sclerosis plaques.
• Parenchymal and leptomeningeal contrast enhancement is noted in 35% of cases.
• MR angiography demonstrates contour irregularities, segmental stenoses, and dilatations of medium-sized intracranial vessels.

Intracranial hemorrhages (e.g., parenchymal hematomas) are rare in angiitis. A definitive diagnosis requires a brain biopsy, which reveals segmental inflammation of small arterioles with an intact tunica media.

Reversible cerebral vasoconstriction syndrome (RCVS)

RCVS is the most frequent mimic of primary CNS angiitis. It is a group of disorders characterized by multifocal segmental vasoconstriction of cerebral arteries, often accompanied by acute thunderclap headaches (thunderclap headache).

The condition is often triggered by vasoactive substances (decongestants, amphetamines, ergotamine derivatives), recreational drugs, contraceptives, as well as late pregnancy or sexual intercourse.

MRI features in RCVS: Unlike angiitis, baseline brain MRI in uncomplicated RCVS is typically normal. Abnormalities on tomograms appear only when specific complications develop:

1. Cortical subarachnoid hemorrhage (in 22% of cases).
2. Posterior reversible encephalopathy syndrome — PRES (9%).
3. Intracerebral hemorrhage (6%).
4. Cerebral infarction (4%).

At the same time, cerebral angiography clearly demonstrates multifocal segmental vasoconstriction. An important feature of the syndrome is the complete or substantial reversibility of these changes within approximately 3 months.

Intervention planning

In addition to diagnosing vasculitis and vasospasm, arterial imaging is critically important when preparing for surgery. CT angiography (CTA) or MR angiography is strongly recommended for planning percutaneous interventions (biopsies, ablations, drainages) near major arteries. This provides the operator with an accurate anatomical map and prevents accidental damage to vital vascular structures.

Class and exam questions

What else to study on this topic

• Stroke imaging: assessment of perfusion-diffusion mismatch.
• Indications for endovascular thrombectomy in stroke and clinical-radiological mismatch.
• Diagnostic imaging of cervical artery dissection (CT and MRI).
• Imaging features of cerebral venous thrombosis and arteriovenous malformations (AVMs).
• Subclavian steal syndrome and its hemodynamic manifestations.

Other topics in the Neuroimaging section

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