Giant Basilar Artery Aneurysm: Pathophysiology, MRI Diagnosis, Imaging Features, Treatment, and Prognosis | Neurovascular Imaging Review

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 Giant Basilar Artery Aneurysm: Pathophysiology, MRI Diagnosis, Imaging Features, Treatment, and Prognosis | Neurovascular Imaging Review



Introduction: Giant Basilar Artery Aneurysm as a Critical Neurovascular Emergency

The Giant Basilar Artery Aneurysm represents one of the most complex and life-threatening entities in neurovascular medicine. This rare but devastating form of intracranial aneurysm arises within the basilar artery, the central vessel supplying the brainstem, cerebellum, and posterior cerebral circulation. Due to its location within the posterior circulation, even gradual enlargement may result in severe neurological deterioration, while rupture can lead to catastrophic subarachnoid hemorrhage and death.

The present case involves a 47-year-old right-handed woman presenting with progressive occipital headache, cognitive impairment, and personality change, with imaging revealing a giant basilar artery aneurysm measuring approximately 3.5 × 4.0 cm. These clinical and radiological features exemplify the devastating potential of posterior circulation aneurysms and underscore the importance of early diagnosis with MRI and MRA.

This comprehensive expert review will examine the pathophysiology, epidemiology, clinical presentation, imaging characteristics, differential diagnosis, diagnostic approach, treatment strategies, and prognosis of giant basilar artery aneurysm based on the most authoritative global medical literature.

Case Presentation and Imaging Findings

Clinical History

A 47-year-old right-handed woman presented with:

  • Progressive occipital headache for 3 months
  • Progressive confusion
  • Personality changes

Neurologic examination demonstrated:

  • Mild impairment of smooth pursuit eye movements
  • Mild tandem gait impairment
  • Kokmen Short Test of Mental Status score: 30/38

These findings suggest progressive brainstem compression and cognitive dysfunction caused by mass effect from an expanding vascular lesion.

Imaging Findings and Radiologic Interpretation

MRI Brain


Figure 1 Caption and Radiologic Interpretation:

MRI demonstrates a large, cylindrical lesion centered within the midbrain, with mass effect and compression of adjacent brainstem structures. The lesion demonstrates signal characteristics consistent with a partially thrombosed aneurysm. Associated obstructive hydrocephalus is evident due to compression of the cerebral aqueduct.

This finding strongly suggests a giant basilar artery aneurysm exerting significant brainstem compression.

Magnetic Resonance Angiography (MRA)

Figure 2 Caption and Radiologic Interpretation:

Magnetic resonance angiography demonstrates a large saccular aneurysm arising from the basilar artery measuring approximately 3.5 × 4.0 cm. A flow-related signal is seen within the aneurysm lumen, confirming its vascular origin.

The aneurysm is centered along the basilar trunk and demonstrates significant dilation relative to normal arterial diameter.

MRI Brain Additional View

Figure 3 Caption and Radiologic Interpretation:

Additional MRI views demonstrate extensive mass effect on the midbrain and pons, with surrounding edema and distortion of normal brainstem anatomy. Secondary obstructive hydrocephalus is present.

These findings confirm the diagnosis of a giant basilar artery aneurysm causing compressive brainstem dysfunction.

Definition of Giant Basilar Artery Aneurysm

A giant intracranial aneurysm is defined as an aneurysm measuring ≥ 25 mm in diameter.

Giant basilar artery aneurysms are particularly dangerous due to:

  • Brainstem compression
  • Risk of rupture
  • Progressive neurological decline
  • Complex surgical management

Pathophysiology of Giant Basilar Artery Aneurysm

The pathophysiology involves progressive weakening of the arterial wall due to structural and hemodynamic abnormalities.

Structural Mechanisms

Key structural changes include:

  • Degeneration of the internal elastic lamina
  • Smooth muscle cell loss
  • Collagen degradation
  • Wall thinning and remodeling

These changes result in vessel wall weakness and progressive aneurysmal dilation.

Hemodynamic Factors

The basilar artery experiences unique hemodynamic stress due to:

  • High flow velocity
  • Bifurcation-related turbulence
  • Shear stress at vessel walls

Chronic hemodynamic stress promotes progressive aneurysm growth.

Thrombosis and Mass Effect

Giant aneurysms frequently develop intraluminal thrombosis, which:

  • Alters flow dynamics
  • Promotes further growth
  • Causes brainstem compression

This explains the progressive neurological symptoms seen in this case.

Epidemiology of Giant Basilar Artery Aneurysm

Intracranial aneurysms affect approximately:

  • 3–5% of the general population

Posterior circulation aneurysms represent:

  • 10–15% of intracranial aneurysms

Giant aneurysms represent only:

  • 5% of intracranial aneurysms

Basilar artery aneurysms are among the rarest but most dangerous.

Risk factors include:

  • Hypertension
  • Smoking
  • Female sex
  • Genetic predisposition
  • Connective tissue disorders

Clinical Presentation

Clinical symptoms depend on aneurysm size and rupture status.

Symptoms Due to Brainstem Compression

Common symptoms include:

  • Headache
  • Cognitive decline
  • Personality changes
  • Diplopia
  • Gait instability
  • Cranial nerve palsy

These symptoms were present in this case.

Symptoms Due to Rupture

If rupture occurs:

  • Sudden severe headache
  • Loss of consciousness
  • Subarachnoid hemorrhage
  • Death

Mortality rates exceed 50%.

Imaging Features of Giant Basilar Artery Aneurysm

MRI Findings

MRI demonstrates:

  • Large vascular mass
  • Flow void within aneurysm
  • Brainstem compression
  • Hydrocephalus

MRI is best for evaluating:

  • Mass effect
  • Thrombosis
  • Brainstem injury

MRA Findings

MRA demonstrates:

  • Direct visualization of aneurysm lumen
  • Vessel dilation
  • Flow dynamics

MRA is essential for diagnosis.

CT Findings

CT demonstrates:

  • Hyperdense vascular mass
  • Hydrocephalus
  • Calcification

CT angiography provides excellent vascular detail.

Digital Subtraction Angiography (DSA)

Gold standard imaging modality.

Provides:

  • Highest spatial resolution
  • Treatment planning capability

Differential Diagnosis

Conditions that may mimic a giant basilar artery aneurysm include:

1. Brainstem Glioma

Distinguishing features:

  • Solid tumor
  • No vascular flow signal

2. Central Pontine Myelinolysis

Features:

  • Symmetric demyelination
  • No vascular dilation

3. Dandy-Walker Malformation

Features:

  • Congenital abnormality
  • Cerebellar vermis hypoplasia

4. Brainstem Infarction

Features:

  • Acute onset
  • Restricted diffusion

Diagnosis

Diagnosis requires multimodal imaging:

Primary modalities:

  • MRI
  • MRA
  • CTA
  • DSA

MRA and MRI confirmed the diagnosis in this case.

Treatment of Giant Basilar Artery Aneurysm

Treatment depends on aneurysm size, location, and patient status.

Endovascular Treatment (Preferred)

Includes:

Coil embolization

Advantages:

  • Minimally invasive
  • Lower morbidity

Flow diversion stents

Modern preferred treatment

Mechanism:

  • Redirect blood flow
  • Promote aneurysm thrombosis

Surgical Clipping

Rarely used due to the difficulty accessing the basilar artery.

Higher risk than endovascular therapy.

Observation

Only for small asymptomatic aneurysms.

Not appropriate for giant aneurysms.

Prognosis

An untreated giant basilar artery aneurysm carries an extremely poor prognosis.

Mortality:

  • 60–80% at 5 years untreated

Treatment improves survival significantly.

Prognosis depends on:

  • Size
  • Rupture status
  • Treatment success

Early diagnosis improves outcomes.

Clinical Significance and Key Learning Points

Key diagnostic features include:

  • Brainstem compression symptoms
  • Large vascular lesion on MRI
  • Flow signal on MRA
  • Hydrocephalus

Early diagnosis is critical for survival.

Quiz

Question 1. What is the most likely diagnosis?

A. Brainstem glioma
B. Pontine infarction
C. Giant basilar artery aneurysm
D. Multiple sclerosis
E. Dandy-Walker malformation

Answer: C. Explanation: MRI and MRA demonstrate a large vascular lesion consistent with a giant basilar artery aneurysm.

Question 2. What imaging modality is the gold standard?

A. CT
B. MRI
C. Ultrasound
D. Digital subtraction angiography
E. X-ray

Answer: D. Explanation: DSA provides the highest vascular resolution.

Question 3. Most dangerous complication?

A. Seizure
B. Stroke
C. Subarachnoid hemorrhage
D. Infection
E. Edema

Answer: C. Explanation: Rupture causes fatal hemorrhage.

Conclusion

A giant basilar artery aneurysm is one of the most dangerous neurovascular disorders. Early diagnosis using MRI and MRA is essential. Endovascular therapy represents the modern treatment of choice and significantly improves prognosis.

Prompt recognition and expert management are essential for survival.

References

[1] D. Wiebers et al., "Unruptured intracranial aneurysms," New England Journal of Medicine, 2003.

[2] G. Lanzino et al., "Giant intracranial aneurysms," Neurosurgery, 2013.

[3] A. Molyneux et al., "International Subarachnoid Aneurysm Trial," Lancet, 2005.

[4] Rinkel et al., "Epidemiology of intracranial aneurysms," Stroke, 1998.

[5] Lawton et al., "Seven aneurysms," Neurosurgery, 2017.

[6] Brinjikji et al., "Flow diversion treatment," AJNR, 2015.

[7] NEJM Image Challenge DOI: 10.1056/NEJMicm1207982



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