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Arteriovenous Malformations

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About

• Prevalence: Incidence of 20-50 per 100,000; often discovered incidentally on imaging.
• Definition: Direct connection between arteries and veins without a protective capillary bed, exposing veins to high arterial pressure and risk of rupture.

Pathophysiology

• AVMs disrupt normal blood flow and oxygen exchange due to bypassing the capillary network.
• Increased venous pressure can lead to weakened vessel walls and potential rupture.
• Primarily found in cerebral structures but can occur in the spine, dura, and other locations.

Genetics and Inheritance

• Hereditary Hemorrhagic Telangiectasia (HHT): 10-25% of patients with HHT have brain AVMs.
• Generally occur sporadically, with familial cases being rare.
• Equally distributed between males and females.

Inherited Conditions Associated with AVMs

Condition	Description
Sturge-Weber Syndrome	Marked by facial port-wine stain, neurological abnormalities, and brain hemangiomas. AVMs are rare but leptomeningeal angiomatosis can cause seizures and hemiparesis.
Hereditary Haemorrhagic Telangiectasia	A genetic disorder leading to abnormal blood vessel formation, including AVMs. Symptoms include frequent nosebleeds, telangiectasias, and visceral AVMs.

Clinical Presentation

• Incidental Findings: Often asymptomatic, detected during imaging for unrelated conditions.
• Headache: May be chronic or severe, especially if bleeding occurs.
• Seizures: Focal or generalized; AVMs are a common cause of seizures in younger patients.
• Neurological Deficits: May include visual disturbances, weakness, numbness, or speech difficulties.
• Tinnitus: Audible bruit may be present in larger AVMs.

Complications

• Intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH).
• Progressive neurological deficits due to mass effect or hemorrhage.
• Seizure disorders, especially with cortical involvement.
• Hydrocephalus from obstruction of cerebrospinal fluid (CSF) pathways.

Spetzler-Martin Grading of AVMs

This grading system assesses the risk of surgical intervention:

• Nidus Size: Small (<3cm) = 1, Medium (3-6cm) = 2, Large (>6cm) = 3.
• Eloquence of Adjacent Brain: Non-eloquent = 0, Eloquent = 1.
• Venous Drainage: Superficial only = 0, Deep = 1.
• Total Grades: Higher grades correlate with higher surgical risk.

Investigations

• CT Scan: Often first-line imaging for suspected intracerebral hemorrhage. AVMs may appear as high-density lesions, with or without calcification.
• MRI: Provides detailed visualization of AVM structure and surrounding brain tissue. T2-weighted MRI can reveal flow voids indicative of vascular lesions.
• Cerebral Angiography: Gold standard for AVM diagnosis, essential for treatment planning.
• Electroencephalogram (EEG): Assesses seizure activity in patients presenting with epilepsy.

Management

Conservative Management

• Asymptomatic or low-grade AVMs may be managed conservatively to avoid intervention risks.
• Regular imaging to monitor AVM size and integrity.

Surgical Removal

• Indicated for accessible AVMs in non-eloquent brain regions (Spetzler-Martin grades I-II).
• Preferred for smaller, surgically accessible AVMs.

Radiosurgery

• Focal Beam Radiotherapy: Used for deep or surgically challenging AVMs. Radiation induces vessel fibrosis, leading to gradual obliteration over 1-3 years.
• Stereotactic Radiosurgery (SRS): Highly focused radiation is used to scar the AVM, eventually causing it to clot off.

Endovascular Embolization

• Embolic agents are injected to block feeding arteries, reducing AVM size or stabilizing the lesion pre-surgery.
• Often combined with surgery or radiosurgery.

AHA Recommendations for AVM Management

• Unruptured AVMs: Patients should be informed about the hemorrhage risk (~1% per year) and seizure risk (~8% over five years). Conservative management is often preferred for asymptomatic AVMs due to treatment risks.
• Ruptured AVMs: Risk of rebleeding is higher (~5% per year). Imaging (CTA, MRA, DSA) is recommended for diagnostic clarity, with treatment tailored to risks versus benefits.

Prognosis

• Early Detection: Smaller, accessible AVMs generally have a favorable outcome post-resection.
• Risk Factors: AVMs with deep venous drainage or associated aneurysms carry a higher rebleeding risk.

References

• Arteriovenous Malformations of the Brain - NEJM
• AHA Stroke Management of Brain AVMs

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