= central embryonic AVM of quadrigeminal plate cistern directly drains into a secondarily enlarged ectatic vein of Galen (aneurysm is a misnomer)

Prevalence:<1% of all vascular brain malformations

Cause: arteriovenous fistula between primitive choroidal vessels and embryonic median prosencephalic vein of Markowski; fistula prevents involution of this embryonic vein + leads to development of the vein of Galen

Anatomical types:

• Type 1 = AV fistula fed by enlarged arterial branches → dilatation of vein of Galen + straight sinus + torcular herophili
• Type 2 = angiomatous malformation involving basal ganglia + thalami ± midbrain draining into vein of Galen
• Type 3 = transitional AVM with both features

Feeding vessels:

1. posterior cerebral artery, posterior choroidal artery (90%)
2. anterior cerebral artery + anterior choroidal artery
3. middle cerebral artery + lenticulostriate + thalamic perforating arteries (least common)

Age at presentation: detectable in utero >30 weeks GA; M÷F = 2÷1

1. neonatal pattern (0–1 month)
   • high-output cardiac failure (36%) ← massive shunting
   • cranial bruit
2. infantile pattern (1–12 months)
   • macrocrania from obstructive hydrocephalus; seizures
3. adult pattern (>1 year)
   • headaches ± intracranial hemorrhage ± hydrocephalus
   • focal neurologic deficits (5%) ← steal of blood from surrounding structures

• Rarely diagnosed >3 years of age

Associated with: anomalous dural sinuses + sinus stenosis

May be associated with: porencephaly, nonimmune hydrops

Location: midline posterior to 3^rd ventricle

Types:

1. Choroidal type
   • multiple prominent choroidal + pericallosal and thalamostriate feeder arteries
   • drainage into anterior aspect of intensely enhancing aneurysmal median prosencephalic vein of Markowski
2. Mural type
   • few prominent posterior choroidal / collicular feeder arteries
   • arteries fistulize with lateral walls of an intensely enhancing median prosencephalic vein of Markowski

→both types drain via persistent falcine sinus into superior sagittal sinus

• prominent serpiginous network of feeding arteries in basal ganglia, thalami, midbrain + nidus + draining veins

NECT:

• round well-circumscribed homogeneous slightly hyperdense mass posterior to indented 3^rd ventricular outlet
• hyperdense intracerebral hematoma ← ruptured AVM
• focal hypodense zones ← ischemic changes
• rim calcification (14%)

CECT:

• marked homogeneous enhancement of serpentine structures + vein of Galen + dilated straight + transverse sinus + torcular herophili

US / OB-US:

• anechoic tubular midline structure superior to cerebellum
• cardiac enlargement ← high-output heart failure
• dilated veins of head + neck
• hydrocephalus with dilatation of lateral + 3^rd ventricle (in 37%) ← aqueductal obstruction / posthemorrhagic impairment of CSF absorption
• brain infarction / leukomalacia ← steal phenomenon with hypoperfusion

Doppler US:

• median tubular cystic space with high-velocity turbulent flow
• variable thrombus + feeding vessels
• tortuous network of dilated arteries

MR:

• areas of signal void

Angio:

• necessary to define vascular anatomy for surgical / endovascular intervention

Cx: subarachnoid hemorrhage

Rx: ligation, excision, embolization of vessels from transtorcular / transarterial approach

Prognosis: 56% (91%) overall (neonatal) mortality: death from cardiac + multisystem failure if untreated

DDx:

1. Aneurysmal dilatation of vein of Galen (= thalamic arteriovenous malformation of brain with deep venous drainage into secondarily dilated vein of Galen)
2. Dural AV fistula
3. Giant developmental venous anomaly
4. Pineal tumor
5. Arachnoid / colloid / porencephalic cyst