Cerebrovascular Evaluation and Stroke Risk

Study Notes

Cerebrovascular Evaluation

Cerebrovascular evaluation is a process to assess the health of blood vessels supplying the brain.
Non-modifiable risk factors for stroke include age, sex, race, and family history of cerebrovascular disease.
Modifiable risk factors include hypertension, atrial fibrillation, other cardiac diseases, diabetes mellitus, elevated cholesterol, smoking, and a sedentary lifestyle/poor diet.
Patients may present with or without symptoms.
Stroke is the fourth leading cause of death in the US, with 85% resulting from ischemia. Other causes include hemorrhage and vasospasm.
Atherosclerosis in the carotid bifurcation is the most frequent cause of stroke.

Terminology

Transient Ischemic Attack (TIA): Symptoms lasting less than 24 hours.
Reversible Neurological Deficit (RIND): Symptoms resolve over 24-72 hours.
Cerebrovascular Accident (CVA): Permanent symptoms or damage.
Brain Infarction: Insufficient blood supply to the brain due to stenosis or occlusion.
Subarachnoid Hemorrhage: Rupture of intracranial vessels.
Hemiparesis/Hemiplegia: Weakness/paralysis on one side of the body (symptoms depend on affected brain hemisphere).

Carotid Anatomy and Evaluation

Common Carotid Artery (CCA):
- Originates from the innominate artery (right) and aortic arch (left).
- Courses cephalad along the anterolateral neck.
- Distal portion enlarges to form the carotid bulb, then branches into the internal and external carotid arteries.
- Bifurcates at the level of the thyroid cartilage.
- ICA and ECA flow exhibit higher resistance with good diastolic flow.
- Color Doppler identifies flow separation and short periods of systolic flow reversal.
External Carotid Artery (ECA):
- Smaller diameter than the internal carotid artery.
- Branches supply the neck, thyroid, face, and scalp.
- High resistance, pulsatile flow with minimal antegrade diastolic flow.
- The superficial temporal artery is often used for the temporal tap technique.
- Important branches include: Superior Thyroidal, Ascending Pharyngeal, Lingual, Facial, Maxillary, Occipital, Posterior Auricular, and Superficial Temporal.
Internal Carotid Artery (ICA):
- Larger diameter than the external carotid artery.
- Courses cephalad into the cranium.
- Distal ICA forms an S-shaped curve (siphon) increasing risk of flow-reducing lesions (atheromas, thrombus).
- No visible extracranial branches.
- Important branch: Ophthalmic artery (branches into nasal, frontal, and supraorbital arteries)
- Supplies 75% of arterial blood to the brain.
- Low resistance flow with increased antegrade diastolic flow.
- Important branches include: Anterior choroidal, and posterior communicating arteries (parts of circle of Willis)

Vertebral and Basilar Arteries

Vertebral Arteries:
- Supply 10-25% of blood flow to the brain.
- Course within the transverse foramina of C1 through C6 vertebrae, entering the skull through the foramen magnum.
- Converge to form the basilar artery after entering posterior skull.
- Provides branches to the medulla and inferior cerebellum.
- Vertebral arteries should always demonstrate antegrade flow.
Basilar Artery:
- Formed by the fusion of the left and right vertebral arteries at the base of the skull.
- Branches supply the superior cerebellum and brain stem.
- Bifurcates at the circle of Willis to form both posterior cerebral arteries.

Circle of Willis

A network of arteries seated on the inferior cerebrum surface, supplying all lobes of the cerebrum.
Most patients do not show a complete circle of Willis but the potential for flow re-routing exists if an area is blocked.

Anterior, Middle, and Posterior Cerebral Arteries

Branches of the circle of Willis that supply blood to specific brain lobes.
- ACA: Frontal and parietal lobes.
- MCA: Frontal, parietal, and temporal lobes.
- PCA: Temporal and occipital lobes.

ICA Disease Symptoms

Unilateral symptoms with contralateral side stenosis.
Paresthesia (tingling sensation).
Paresis (weakness).
Paralysis (loss of movement).
Broca's Aphasia (language dysfunction).
Amaurosis Fugax (temporary partial or complete vision loss).

Vertebral/Basilar Disease Symptoms

Vertigo (dizziness and loss of balance).
Ataxia (lack of coordination).
Bilateral visual blurring or double vision.
Homonymous hemianopia (loss of half of the visual field in both eyes).
Bilateral paresthesia.
Drop attacks (sudden falling to the ground).
Dysphagia (difficulty swallowing).

Other Important Information

Carotid bruits (turbulent blood flow) heard during systole and diastole often indicate significant stenosis.
Color Doppler evaluation helps determine atherosclerosis and flow disturbances.
Image assessment is important in these evaluations.