General Principles

• Cerebral vascular malformations are a heterogeneous group of abnormal vascular structures involving arteries, capillaries, or veins
• Classification is based on the McCormick histological system — four main types: AVM, cavernous malformation, dAVF, and DVA
• Key distinguishing features: flow type (high vs. low), presence of intervening brain parenchyma, hemorrhage risk, and angiographic visibility
• Capillary telangiectasias represent a fifth, typically incidental, category

Comprehensive Comparison of Vascular Malformations

Pathology & Pathophysiology

Structure

• Nidus: tangled network of dysplastic vessels forming direct arteriovenous shunts — no intervening capillary bed
• Feeding arteries: enlarged, high-flow arteries supplying the nidus; may develop flow-related aneurysms (7–20% of cases)
• Draining veins: arterialized veins carrying high-pressure oxygenated blood; prone to rupture
• Brain parenchyma is interspersed within the nidus (distinguishes from cavernoma)
• Gliosis and hemosiderin deposits surround the nidus

Hemodynamics

• Arteriovenous shunting: low-resistance pathway → high flow through nidus
• Steal phenomenon: blood diverted from adjacent normal brain tissue → chronic hypoperfusion → progressive neurological deficits
• Venous hypertension: arterialized pressure transmitted to venous system → hemorrhage risk, edema
• Associated aneurysms: intranidal (within nidus), flow-related (on feeding arteries), or remote — all increase hemorrhage risk

Epidemiology

• Prevalence: ~0.1% (1 in 1,000); incidence ~1 per 100,000 per year
• Typically present in young adults (20–40 years); most diagnoses before age 50
• No sex predominance; slight male predilection for hemorrhage
• Account for 1–2% of all strokes but up to 33% of hemorrhagic strokes in young adults
• 90% are supratentorial; 10% are infratentorial (higher hemorrhage risk)

Clinical Presentation

Hemorrhage (Most Common — 50–65%)

• Annual hemorrhage risk: 2–4% per year for unruptured; ~4.5% per year in first year after initial hemorrhage
• Lifetime risk approximation (simplified): 105 − patient age (in years) = approximate lifetime risk in %
• Typically intraparenchymal; may extend to subarachnoid or intraventricular space
• AVM hemorrhage generally has lower mortality than hypertensive ICH (~10% vs. ~40%)

Seizures (20–25%)

• More common with cortical AVMs, especially frontal and temporal locations
• Mechanism: gliosis, hemosiderin deposition, ischemia from steal phenomenon
• May be the presenting symptom, especially with large superficial AVMs

Headache (15%)

• Migraine-like headaches, sometimes with aura
• May mimic cluster headaches if in posterior fossa

Progressive Neurological Deficits (5–10%)

• Vascular steal: chronic hypoperfusion of adjacent brain tissue
• Progressive hemiparesis, cognitive decline, or visual field deficits
• More common with large, high-flow AVMs

Hemorrhage Risk Factors

• Prior hemorrhage (strongest risk factor; recurrent hemorrhage rate ~4.5%/year in first year)
• Deep location (basal ganglia, thalamus, brainstem)
• Deep venous drainage (single deep draining vein)
• Associated aneurysms (intranidal or feeding artery)
• Small nidus size (paradoxically higher pressure per vessel)
• Infratentorial location
• Venous outflow stenosis or restriction

Spetzler-Martin Grading Scale

Grading Components

Interpretation

ARUBA Trial

Study Design & Key Findings

• A Randomized trial of Unruptured Brain AVMs (ARUBA) — published 2014, New England Journal of Medicine
• Population: 226 patients with unruptured AVMs randomized to medical management alone vs. interventional therapy (surgery, embolization, radiosurgery, or combination)
• Primary outcome: Stroke or death
• Result: Medical management was superior to intervention — event rate 10.1% (medical) vs. 30.7% (intervention) at mean follow-up of 33 months
• Risk ratio: 0.27 (95% CI 0.14–0.54) favoring medical management
• Trial stopped early due to superiority of medical management

Criticisms & Limitations

• Short follow-up (33 months) — AVMs are lifelong conditions; benefits of treatment may emerge over decades
• Heterogeneous treatment arm: mixed surgical, endovascular, and radiosurgery approaches; not all centers were high-volume
• Selection bias: excluded high-grade (IV–V) AVMs, but also included many low-grade AVMs that might not have been treated in practice
• No stratification by Spetzler-Martin grade within the intervention arm
• Radiosurgery effects take 2–3 years for full obliteration — short follow-up may underestimate benefit
• Many AVM specialists continue to recommend treatment for low-grade (I–II) AVMs in young patients

Treatment Options

Microsurgical Resection

• Gold standard for Spetzler-Martin grades I–III
• Provides immediate and complete cure if total resection is achieved
• Cure rate: >95% for grades I–II
• Risk of normal perfusion pressure breakthrough (NPPB): after removal of high-flow AVM, surrounding brain may develop edema/hemorrhage from loss of autoregulation
• Staged embolization before surgery reduces nidus size and intraoperative blood loss

Stereotactic Radiosurgery (Gamma Knife / CyberKnife)

• Best for small (<3 cm) and deep AVMs not amenable to surgery
• Obliteration rate: ~80% at 3 years for lesions <3 cm
• Delayed effect: 2–3 years for complete obliteration via radiation-induced vessel wall thickening and thrombosis
• Patient remains at hemorrhage risk during the latency period
• Adverse effects: radiation necrosis, edema, cyst formation

Endovascular Embolization

• Primarily used as adjunctive therapy before surgery or radiosurgery to reduce nidus size
• Rarely curative as monotherapy (<20% complete obliteration); highest success with small AVMs with few feeders
• Embolic agents: n-butyl cyanoacrylate (nBCA/Onyx), coils, particles
• Risks: stroke, hemorrhage (from premature venous occlusion), cranial nerve injury
• Targeted embolization of associated aneurysms reduces hemorrhage risk

Multimodal Approach

• Combines embolization + surgery, or embolization + radiosurgery
• Particularly useful for grade III AVMs
• Embolization reduces nidus volume → improves surgical safety or radiosurgery effectiveness

Hereditary Hemorrhagic Telangiectasia (HHT) / Osler-Weber-Rendu Syndrome

Genetics & Pathophysiology

• Autosomal dominant disorder of vascular dysplasia
• HHT1: ENG gene (endoglin) on chromosome 9 → higher risk of pulmonary and cerebral AVMs
• HHT2: ACVRL1 gene (ALK1) on chromosome 12 → higher risk of hepatic AVMs
• Juvenile polyposis-HHT overlap: SMAD4 gene
• Prevalence: ~1 in 5,000–8,000

Clinical Features (Curaçao Criteria — need ≥3 for definite diagnosis)

• Epistaxis: spontaneous, recurrent nosebleeds (most common feature, >90%)
• Telangiectasias: lips, oral mucosa, fingers, nose
• Visceral AVMs: pulmonary (30–50% in HHT1), hepatic (30–70% in HHT2), cerebral (10–20%), GI, spinal
• Family history: first-degree relative with HHT

Neurological Complications

• Cerebral AVMs: present in 10–20% of HHT patients (especially HHT1); often multiple, small
• Brain abscess: from paradoxical embolism through pulmonary AVMs (bypassing pulmonary capillary filter)
• Ischemic stroke: paradoxical embolism through pulmonary AVMs
• Spinal AVMs: less common but may cause myelopathy
• Screening: all HHT patients should undergo brain MRI and contrast echocardiography (bubble study) for pulmonary AVMs

Pathology

• Clusters of thin-walled sinusoidal vascular channels lined by a single layer of endothelium
• No intervening brain parenchyma between vascular channels (key distinction from AVM)
• No smooth muscle or elastic lamina in vessel walls → fragile, prone to microhemorrhages
• “Mulberry-like” or “raspberry-like” gross appearance
• Low-flow lesion: no arterial feeders, no high-flow arterialization
• Surrounded by a rim of hemosiderin-laden macrophages and gliotic brain parenchyma (evidence of repeated microhemorrhages)
• May contain calcification, organized thrombus, and cholesterol clefts

Epidemiology

• Prevalence: 0.4–0.8% of the general population (autopsy and MRI studies)
• Second most common vascular malformation after DVAs
• Peak presentation: 20–40 years of age
• Equal sex distribution
• Location: 70–80% supratentorial, 10–20% brainstem, 5% spinal cord
• Most are solitary (sporadic cases); multiple lesions suggest familial form

Genetics: Familial vs. Sporadic

Sporadic Form (~80%)

• Usually solitary lesion
• Somatic mutations; often associated with a nearby DVA
• May develop de novo, especially after radiation therapy

Familial Form (~20%)

• Autosomal dominant inheritance with variable penetrance
• Multiple lesions (often dozens); number increases with age
• More prevalent in Hispanic Americans of Mexican descent (founder CCM1 mutation)

Clinical Presentation

Seizures (Most Common — 40–70%)

• Most common presenting symptom, especially for supratentorial cavernomas
• Mechanism: hemosiderin deposition and gliosis irritate surrounding cortex
• Often focal seizures with or without secondary generalization
• May be medically refractory; surgical resection achieves seizure freedom in ~70–80%

Hemorrhage (5–30% at presentation)

• Annual hemorrhage rate: 0.5–1% per lesion-year (sporadic); higher in familial forms
• After first hemorrhage: rebleed risk increases to ~4–5% per year (clustering phenomenon in first 2–3 years)
• Hemorrhages are typically small, contained (low-flow) — less catastrophic than AVM hemorrhage
• Brainstem cavernomas: even small hemorrhages can produce devastating deficits

Progressive Focal Neurological Deficits

• Repeat microhemorrhages → progressive enlargement → mass effect
• Especially significant in brainstem cavernomas: cranial nerve palsies, long tract signs, ataxia

Headache

• Less specific; may be related to subclinical hemorrhages

Imaging

MRI (Modality of Choice)

• T1: Mixed signal (methemoglobin from subacute blood products); variable intensity
• T2: Classic “popcorn” or “mulberry” appearance — heterogeneous core of mixed-age blood products with dark hemosiderin ring
• T2*/GRE (gradient echo) and SWI (susceptibility-weighted imaging): Most sensitive sequences for detection; hemosiderin blooms as dark signal (“black dots”)
• SWI detects lesions missed by conventional sequences — essential for screening familial cases
• Minimal or no enhancement with gadolinium
• Zabramski classification: Type I (acute hemorrhage) through Type IV (SWI-only “dot” lesions)

Conventional Angiography (DSA)

• Angiographically OCCULT — no visible lesion on catheter angiography
• Low-flow channels are below the resolution of angiography
• This is a key distinguishing feature from AVMs and dAVFs

CT

• May show calcification or hyperdensity (acute blood)
• Insensitive for diagnosis; MRI is far superior

Brainstem Cavernomas

• Account for 10–20% of all cavernomas
• Higher clinical significance: densely packed critical structures → even small hemorrhages cause major deficits
• Annual hemorrhage rate may be higher (~2–5% per year) once symptomatic
• Symptoms: cranial nerve palsies, hemiparesis, ataxia, vertigo, diplopia, dysphagia
• Surgical decision is difficult: balance hemorrhage risk vs. surgical morbidity
• Surgery recommended if: lesion abuts a pial surface, recurrent symptomatic hemorrhages, progressive deficits
• Timing: optimal surgical window is 2–6 weeks after hemorrhage (lesion expands, creates a plane for dissection)

Treatment

Observation

• For asymptomatic, incidentally discovered lesions
• Serial MRI surveillance (annually, then less frequently)
• Most cavernomas never become symptomatic

Microsurgical Resection

• Symptomatic lesions: recurrent hemorrhage, medically refractory seizures, progressive deficits
• Accessible locations: superficial cortical, temporal (for seizures)
• Seizure freedom rate: ~70–80% (better if resection includes hemosiderin-stained rim)
• Complete resection is curative — no recurrence expected

Anti-seizure Medications

• First-line for seizure management
• Surgery considered for drug-resistant epilepsy

Stereotactic Radiosurgery

• Role is controversial and generally NOT recommended
• Cavernomas are low-flow lesions — radiosurgery is less effective than for AVMs
• Risk of radiation-induced edema in brainstem locations
• Some centers consider it for surgically inaccessible brainstem lesions with recurrent hemorrhage

Pathology & Etiology

• Abnormal direct connection between dural arteries and dural venous sinuses or cortical veins
• Located within the dural leaflets (NOT within brain parenchyma)
• Acquired lesions (NOT congenital) — distinguishes from AVMs
• Account for 10–15% of all intracranial vascular malformations
• Peak incidence: 40–60 years; slight female predominance for cavernous sinus dAVFs

Etiology / Predisposing Factors

• Prior dural sinus thrombosis (most common predisposing factor) — sinus occlusion triggers neoangiogenesis within dural walls
• Head trauma
• Cranial surgery
• Infection (mastoiditis, sinusitis)
• Hypercoagulable states
• Mechanism: sinus thrombosis → venous hypertension → upregulation of VEGF → recruitment of dural arterial feeders → fistula formation

Classification Systems

Cognard Classification

Borden Classification (Simplified)

Clinical Presentation by Location

Transverse-Sigmoid Sinus (Most Common Location)

• Pulsatile tinnitus (most common symptom overall) — synchronous with heartbeat; may be audible to examiner as a bruit
• Objective bruit on auscultation over mastoid
• Headache (ipsilateral, pulsatile)
• Usually benign (Borden I) unless cortical venous drainage develops
• Some resolve spontaneously, especially if related to prior sinus thrombosis that recanalizes

Cavernous Sinus

• Most common in postmenopausal women
• Red eye (arterialization of conjunctival veins)
• Proptosis (increased orbital venous pressure)
• Chemosis (conjunctival edema)
• Cranial nerve palsies: CN III, IV, V₁, VI (within cavernous sinus wall)
• Elevated intraocular pressure → glaucoma
• Often low-grade (Barrow type B–D); many resolve spontaneously or with manual carotid compression
• Must distinguish from direct carotid-cavernous fistula (high-flow, post-traumatic) which is more urgent

Tentorial / Anterior Cranial Fossa

• Highest hemorrhage risk due to preferential cortical venous drainage
• Anterior cranial fossa dAVFs (cribriform plate): fed by ethmoidal arteries (branches of ophthalmic artery) → may present with frontal hemorrhage
• Tentorial dAVFs: drain via cerebellar cortical veins; may present with posterior fossa hemorrhage or progressive cerebellar symptoms
• These locations essentially always have cortical venous drainage → always aggressive (Borden III)

Superior Sagittal Sinus

• Venous hypertension → increased intracranial pressure
• May present with papilledema, headache mimicking pseudotumor cerebri (idiopathic intracranial hypertension)
• Progressive dementia from chronic venous congestion

Imaging

MRI / MRA

• Dilated cortical veins, flow voids in abnormal locations
• Edema in adjacent brain parenchyma (if venous congestion)
• T2 hyperintensity in white matter from venous hypertension
• Time-resolved MRA (TRICKS/TWIST) can demonstrate early venous filling

CT / CTA

• Dilated vessels, prominent dural sinuses
• May show hemorrhage if fistula has ruptured
• CTA can reveal early venous filling and abnormal vascular channels

Digital Subtraction Angiography (DSA)

• Gold standard for diagnosis and classification
• Demonstrates: exact fistula site, arterial feeders, venous drainage pattern, presence/absence of cortical venous drainage
• Must inject both ECA and ICA (some fistulas have pial feeders)
• Key finding: early venous filling in arterial phase

Treatment

Observation

• Appropriate for Borden I / Cognard I dAVFs without cortical venous drainage
• Symptoms manageable (mild tinnitus, headache)
• Some may resolve spontaneously (especially cavernous sinus dAVFs)
• Follow-up imaging to monitor for conversion to higher grade (cortical venous recruitment)

Endovascular Embolization (Primary Treatment)

• Transvenous approach: preferred when sinus is accessible; pack sinus/fistula with coils; high cure rate (~80–90%)
• Transarterial approach: inject liquid embolic (Onyx, nBCA) through feeding arteries to reach fistula point
• Goal: complete disconnection of cortical venous drainage and obliteration of fistula
• Cure rate: 70–90% depending on location and anatomy

Microsurgery

• Disconnection/ligation of arterialized cortical veins at the site of dural penetration
• Best for: anterior cranial fossa dAVFs (ethmoidal feeders difficult to embolize), surgically accessible locations
• High cure rate with low morbidity for properly selected cases

Stereotactic Radiosurgery

• Reserved for dAVFs not amenable to endovascular or surgical treatment
• Latency period of 1–3 years before obliteration
• Patient remains at risk during latency — less ideal for aggressive types
• Obliteration rate: ~60–80%

Overview

• Most common cerebral vascular malformation (60% of all)
• Also called venous angiomas
• Represent a normal anatomical variant of venous drainage, NOT a true malformation
• Prevalence: ~2.5–3% of the population (autopsy and MRI studies)
• Found incidentally on imaging studies performed for other reasons

Pathology & Anatomy

• Radially arranged medullary (white matter) veins converging on a single large collecting vein
• “Caput medusae” appearance: multiple small veins draining into one dilated central vein (like Medusa’s head)
• The collecting vein drains into either a superficial cortical vein or a deep subependymal vein
• Normal brain parenchyma between the venous radicles
• Represent the dominant or sole venous drainage for the surrounding brain tissue

Imaging

• Contrast-enhanced MRI: enhancing “caput medusae” — radial veins converging on a single enlarged collector vein (classic “umbrella” or “palm tree” appearance)
• Conventional angiography (DSA): visible in the venous phase; no arterial shunting; normal arterial phase
• No surrounding edema, no hemorrhage, no mass effect
• SWI/GRE may show the veins prominently due to deoxyhemoglobin
• Most common locations: frontal lobe, cerebellum

Clinical Significance

• Almost always benign and asymptomatic
• Hemorrhage is extremely rare (<0.15% per year) — when hemorrhage occurs near a DVA, suspect an associated cavernous malformation
• Occasionally associated with headache or seizures, but causal relationship uncertain
• Thrombosis of the collecting vein can occur (rare) → venous infarction

Association with Cavernous Malformations

• DVAs and cavernomas frequently co-occur — found together in up to 30% of cases
• Cavernomas may develop adjacent to DVAs over time (possibly induced by venous hypertension within the DVA territory)
• When a DVA is found, look for an associated cavernoma (especially on SWI/GRE sequences)
• If hemorrhage occurs near a DVA, the source is almost always the associated cavernoma, not the DVA itself

Overview

• Small clusters of dilated capillary-type vessels with intervening normal brain parenchyma
• Low-flow, low-pressure; thin vessel walls without smooth muscle
• Most common location: pons (other locations: cerebral cortex, dentate nucleus of cerebellum)
• Prevalence: found in ~0.4% of autopsy series; likely much higher with sensitive MRI
• Usually incidental findings on MRI

Imaging

• MRI with contrast: faint “brush-like” enhancement; poorly defined borders
• T2/FLAIR: usually isointense to mildly hyperintense
• SWI/GRE: may show mild blooming artifact
• No mass effect, no surrounding edema, no hemorrhage
• Angiographically occult (too small for DSA detection)
• Can be associated with DVAs (mixed vascular malformations)

Clinical Significance

• Benign, asymptomatic — no treatment needed
• Hemorrhage is exceedingly rare
• No surgical intervention indicated
• Important to recognize on MRI to avoid unnecessary workup or biopsy
• May be part of HHT spectrum (mucocutaneous telangiectasias)

Spinal Dural Arteriovenous Fistula (Spinal dAVF)

Overview

• Most common spinal vascular malformation in adults (70–80% of all spinal vascular malformations)
• Acquired abnormal connection between a radicular artery and a radicular vein within the dural sleeve of a nerve root
• Most common location: thoracolumbar region (T6–L2)
• Demographics: middle-aged to elderly men (80% male, mean age 55–60)

Pathophysiology — Foix-Alajouanine Syndrome

• Fistula transmits arterial pressure into the spinal venous plexus
• Venous congestion and venous hypertension in the perimedullary veins (coronal venous plexus)
• Reduced arteriovenous pressure gradient across the spinal cord → decreased tissue perfusion
• Progressive congestive myelopathy (edema, ischemia, gliosis)
• Foix-Alajouanine syndrome: subacute progressive myelopathy due to spinal venous hypertension
• If untreated, leads to irreversible spinal cord damage

Clinical Presentation

• Progressive paraparesis (ascending weakness of lower extremities)
• Sensory level or stocking-distribution sensory loss; may be patchy and asymmetric
• Bowel and bladder dysfunction (urinary retention, incontinence)
• Pain: back pain, radicular pain, aching lower extremity pain
• Symptoms may worsen with exercise or upright posture (increased venous pressure) and improve with rest
• Progressive course over months to years — often misdiagnosed as spinal stenosis, peripheral neuropathy, MS, or transverse myelitis

Diagnostic Challenge

• Average delay to diagnosis: 1–3 years from symptom onset
• Frequently misdiagnosed due to insidious onset and nonspecific symptoms
• Key clue: progressive myelopathy in an older man with T2 hyperintensity spanning multiple segments + flow voids on dorsal cord surface

Imaging

• Spinal MRI:
  • T2 hyperintensity of the spinal cord (edema), often spanning multiple segments (long segment myelopathy)
  • Flow voids on the dorsal surface of the cord (dilated perimedullary veins) — pathognomonic
  • Cord enhancement on gadolinium (breakdown of blood-spinal cord barrier)
  • Cord expansion in earlier stages; cord atrophy in later stages
• Spinal DSA (gold standard): identifies exact fistula level, feeding artery, draining veins
• MRA (time-resolved) can help localize fistula before DSA

Treatment

• Goal: disconnect fistula to restore normal venous drainage and halt myelopathy progression
• Microsurgical disconnection: ligation of the arterialized vein at the dural penetration point; cure rate >95%; procedure of choice
• Endovascular embolization: inject embolic agent into the fistula via feeding artery; recurrence rate higher (~15–25%) due to reconstitution from collateral feeders
• Prognosis: motor symptoms often improve after treatment; sensory and bladder symptoms may persist if treatment is delayed
• Early diagnosis is critical — deficits from chronic cord damage may be irreversible

Spinal AVMs

Classification

• Intramedullary (Type II): compact or diffuse nidus within spinal cord parenchyma; similar to brain AVMs; young patients; hemorrhage risk
• Perimedullary fistula (Type III/IV): direct fistula on the pial surface of the cord; variable flow; may present with hemorrhage or myelopathy
• Metameric/juvenile (Cobb syndrome): extensive malformation involving multiple tissue levels (skin, bone, spinal cord) in same metamere

Clinical Features

• Subarachnoid hemorrhage (spinal SAH) — more common than in spinal dAVFs
• Progressive myelopathy
• Radiculopathy
• More common in younger patients (contrast with dAVFs in older adults)

Treatment

• Endovascular embolization (primary approach for perimedullary fistulas)
• Microsurgery for accessible intramedullary lesions
• Often multimodal approach
• Goal: eliminate AVM while preserving spinal cord function