What is the diagnostic approach for basilar artery dissection?

Diagnosis of Basilar Artery Dissection

CT angiography (CTA) of the head and neck with IV contrast is the preferred initial diagnostic modality for basilar artery dissection, demonstrating the highest sensitivity (100%) compared to MRA (77%) and Doppler ultrasound (71%). 1, 2

Clinical Presentation and Suspicion

Maintain a high index of clinical suspicion as basilar artery dissection presents with non-specific symptoms that can mimic other conditions, leading to diagnostic delays. 1

• Common symptoms include headache, neck pain (especially with recent trauma), loss of consciousness, nausea, vomiting, dizziness, double vision, vertigo, and imbalance. 1
• Physical examination findings may reveal ataxia (particularly truncal ataxia), nystagmus, cranial nerve palsies, and visual field defects. 1
• Severe presentations can include locked-in syndrome, progressive brainstem compression signs, or coma. 1, 3, 4
• Critical pitfall: Patients can present with NIHSS score of 0 despite having significant posterior circulation pathology, with symptoms limited to headache, vertigo, and nausea only. 1

Imaging Algorithm

First-Line Imaging: CTA Head and Neck with IV Contrast

CTA should be the initial vascular imaging study as it provides the highest diagnostic sensitivity and allows comprehensive evaluation of the entire vertebrobasilar system. 1, 2

• Sensitivity: 100% for vertebral artery dissection (which can extend to or cause basilar artery involvement). 1, 2
• Key diagnostic features include luminal filling defects, dissection flap, double lumen, pseudolumen, and vessel irregularity. 1
• Coverage requirement: Image the entire vertebral artery from its origin at the aortic arch branch vessels through the basilar artery, as dissection can involve any portion. 1, 2
• Additional findings: CTA can identify the hyperdense basilar artery sign (sensitivity 71%, specificity 98% for basilar occlusion), though this is more specific for thrombotic occlusion. 1

Non-Contrast CT Head

Obtain non-contrast CT initially to exclude hemorrhage and evaluate for mass effect in the posterior fossa, though it has limited sensitivity for detecting dissection itself. 1

• Utility: Rules out subarachnoid hemorrhage (which can occur with ruptured dissection) and identifies life-threatening edema or mass effect. 1
• Limitation: Beam hardening artifact limits assessment of posterior fossa structures. 1

MRI with MRA: Alternative or Complementary Imaging

MRI with MRA and vessel wall imaging sequences provides excellent diagnostic capability when CTA is contraindicated or when additional characterization is needed. 1, 2, 5

• MRA sensitivity: 77% for vertebral artery dissection compared to conventional angiography. 1, 2
• MRA technique: Contrast-enhanced MRA of the neck provides better vessel evaluation with increased spatial resolution and decreased flow-related artifacts compared to time-of-flight sequences. 1
• Vessel wall MRI (VW-MRI): Emerging technique that can directly visualize intramural hematoma, intimal flap, and vessel wall thickening/enhancement characteristic of dissection. 1, 5
• Classic MRI findings: High signal intensity ring surrounding the central lumen on T1-weighted images (representing intramural hematoma), double lumen, pseudolumen, and intimal flap. 6, 4
• DWI sequences: Most sensitive for detecting brainstem ischemia (though initially normal in 6-10% of posterior circulation strokes), and can calculate pc-ASPECTS for prognostication. 1
• FLAIR imaging: Extent of basilar artery hyperintensity correlates with mortality. 1

Digital Subtraction Angiography (DSA)

Reserve catheter-based angiography for cases where non-invasive imaging is inconclusive or when endovascular intervention is being considered. 2

• Traditional gold standard but now largely supplanted by CTA and MRA due to invasiveness. 2
• Diagnostic features: Double lumen, intimal flap, vessel irregularity, and pseudoaneurysm formation. 6, 3
• Additional utility: Delineates collateral circulation via circle of Willis, which has prognostic significance. 2

Doppler Ultrasound

Doppler ultrasound has limited utility as the primary diagnostic modality for basilar artery dissection. 1, 2

• Sensitivity: Only 71% for vertebral artery dissection. 1, 2
• Major limitation: Cannot adequately visualize dissections beginning above the angle of the mandible (which includes most of the basilar artery). 2
• Operator-dependent: More variable than CTA or MRA. 2

Diagnostic Approach Summary

1. Obtain non-contrast CT head immediately to exclude hemorrhage and mass effect. 1
2. Proceed directly to CTA head and neck with IV contrast as the primary diagnostic study, ensuring coverage from aortic arch to circle of Willis. 1, 2
3. Add MRI with DWI, MRA, and vessel wall sequences if CTA is equivocal, contraindicated, or when additional tissue characterization is needed. 1, 2, 5
4. Consider DSA only when non-invasive imaging is inconclusive or endovascular treatment is planned. 2

Critical Clinical Caveats

• Younger patients (under 45 years) with posterior circulation stroke symptoms warrant particular suspicion for dissection, as it accounts for 10-15% of strokes in this age group. 2
• Trauma history is important but not always present; spontaneous dissection occurs and can affect children. 1, 6, 3
• Basilar artery dissection carries worse prognosis than vertebral artery dissection, with significant morbidity and mortality even with treatment. 3
• Combined imaging modalities (MRI and angiography) are complementary and may be necessary for definitive diagnosis in complex cases. 6, 4