What is the most likely diagnosis and appropriate imaging workup for a patient presenting with new‑onset seizures, focal neurological deficits, severe headache, or intracerebral hemorrhage without trauma or vascular risk factors, suggesting a cranial arteriovenous malformation?

Diagnosis of Cranial Arteriovenous Malformation

When a patient presents with new-onset seizures, focal neurological deficits, severe headache, or intracerebral hemorrhage without trauma or vascular risk factors, the most likely diagnosis is a brain arteriovenous malformation (AVM), and the diagnostic workup must begin with MRI followed by four-vessel catheter angiography as the gold standard for definitive characterization. 1

Clinical Presentations That Suggest AVM

The clinical picture provides critical diagnostic clues:

• Intracranial hemorrhage is the most common presentation, occurring in more than 50% of AVM cases and can manifest as intracerebral, subarachnoid, or intraventricular bleeding 2, 3
• Seizures occur in approximately 20-25% of cases and may be focal or generalized, representing the second most common presentation 2, 4
• Severe headache that is sudden, new-onset, or represents a change in character should raise suspicion, particularly when accompanied by other neurological symptoms 1, 5
• Focal neurological deficits may occur with or without seizure or hemorrhage, depending on the AVM location and size 1, 4

Critical diagnostic red flags that heighten suspicion for AVM include: prodromal headache or neurological symptoms, unusual (non-circular) hematoma shape on imaging, edema disproportionate to hemorrhage timing, and presence of subarachnoid blood component 6

Initial Imaging Workup

First-Line Imaging: MRI

• MRI is the most sensitive initial diagnostic modality, showing characteristic inhomogeneous signal void on T1- and T2-weighted sequences, commonly with hemosiderin suggesting prior hemorrhage 1
• MRI provides critical information detailing the localization and topography of the AVM, which is essential for treatment planning 1, 4
• MRI should be performed without and with contrast to fully characterize the lesion and assess for associated findings 1

Complementary Non-Invasive Vascular Imaging

• CT angiography (CTA) and CT venography (CTV) should be performed immediately in the acute setting, particularly when hemorrhage is present, as they provide reasonable sensitivity for detecting vascular malformations 6
• MR angiography (MRA) can provide noninvasive vascular information but lacks the detail needed to fully characterize feeding artery aneurysms, comprehensive venous drainage patterns, or subtle nidus architecture 1
• Time-of-flight and contrast-enhanced MRA demonstrate good agreement with catheter angiography for AVM location and general architecture, but have limited sensitivity for small nidus (<1 cm) or complete resolution after treatment 1

Gold Standard: Catheter Angiography

• Four-vessel cerebral angiography remains the gold standard for definitive AVM diagnosis and characterization, providing submillimeter resolution of arterial and venous anatomy 1, 7
• Catheter angiography should be strongly considered when initial non-invasive studies are negative or suggest vascular pathology, as small vascular malformations may be missed on CTA/MRA 6, 4
• Superselective angiography provides essential information about feeding arteries, nidus architecture, intranidal aneurysms, and venous drainage patterns that are critical for treatment planning 1, 8

Diagnostic Algorithm

Step 1: In patients presenting with new-onset seizures, focal deficits, severe headache, or hemorrhage without clear etiology:

• Obtain MRI brain without and with contrast as the initial diagnostic study 1, 4
• If hemorrhage is present or suspected acutely, perform CTA/CTV immediately 6

Step 2: When MRI or CTA suggests vascular malformation:

• Proceed directly to four-vessel catheter angiography for definitive characterization 1, 6

Step 3: If initial non-invasive imaging is negative but clinical suspicion remains high:

• Do not omit catheter angiography, as small AVMs may be missed on non-invasive studies 6, 4

Key Diagnostic Pitfalls to Avoid

• CT without contrast has low sensitivity for AVM detection; calcification and hypointensity may be noted, but enhancement is only seen after contrast administration 1
• Never dismiss constant pulsatile tinnitus as benign—it warrants comprehensive vascular imaging even without other neurological symptoms, as it may indicate high-flow AVM 7
• Small vascular malformations (<1 cm) are frequently missed on non-invasive imaging, necessitating catheter angiography when clinical suspicion persists 1, 6
• MRA lacks temporal resolution for hemodynamic assessment and cannot adequately evaluate small angioarchitecture details critical for treatment planning 1, 7

Additional Diagnostic Considerations

• Hereditary hemorrhagic telangiectasia (HHT) should be considered in any patient presenting with multiple AVMs of the nervous system 2
• Coagulation studies and complete blood count should be obtained to exclude underlying hemostatic disorders that could contribute to hemorrhage 6
• Associated intranidal or feeding artery aneurysms increase hemorrhage risk and must be identified, as they are more common in children than adults 2
• In young patients (<45 years) with intracerebral hemorrhage, the annual hemorrhage risk from untreated AVM is 2-4% with 10-30% mortality from first hemorrhage 2, 7