Classic Brain (Pial) AVM

◊Most common type of symptomatic vascular malformation!

Diagnostic criteria:

1. presence of a nidus = racemose tangle of abnormal dilated tortuous arteries + veins embedded within parenchyma
   • glomerular / compact nidus = abnormal vessels without any interspersed normal brain tissue
   • diffuse / proliferative nidus = interspersed normal brain parenchyma (2–4%)
2. early venous drainage

Histo: affected arteries have thin walls (no elastica, small amount of muscularis)

Prevalence: 0.02–0.15% for sporadic AVM; 2% for syndromic AVM (hereditary hemorrhagic telangiectasia, cerebrofacial AV metameric syndrome)

Peak age: 20–40 years; 80% by end of 4^th decade; 20% <20 years of age; M=F

Associated with: aneurysm in feeding artery in 10%

• headaches, seizures (nonfocal in 40%), mental deterioration
• progressive hemispheric neurologic deficit (50%)
• ictus from acute intracranial hemorrhage (50%): multicompartmental in 31%, subarachnoid in 30%, parenchymal in 23%, intraventricular in 16%

Location: usually solitary; in 2% multiple

1. supratentorial (90%): parietal >frontal >temporal lobe >paraventricular >intraventricular region >occipital lobe
2. infratentorial (10%)

Site:

1. superficial / cortical:
   • supply via pial arteries = branches of ACA, MCA, PCA;
   • drainage via cortical veins
2. deep / ventricular:
   • supply via lenticulostriate, thalamoperforator branches, anterior / medial / lateral / posterior choroidal arteries
   • drainage via deep venous system

Vascular supply:

1. pial branches of ICA in 73% of supratentorial location, in 50% of posterior fossa location
2. dural branches of ECA in 27% with infratentorial lesions
3. mixed

• NO mass effect (due to replacement of normal brain tissue) unless complicated by hemorrhage + edema:
  • intraparenchymal / intraventricular / subarachnoid hemorrhage
• adjacent parenchymal atrophy ← vascular steal + ischemia

Skull film:

• speckled / ringlike calcifications (15–30%)
• thinning / thickening of skull at contact area with AVM
• prominent vascular grooves on inner table of skull (= dilated feeding arteries + draining veins) in 27%

NECT:

• irregular lesion with large feeding arteries + draining veins
• mixed density (60%): dense large vessels + hemorrhage + calcifications
• isodense lesion (15%): recognizable by mass effect
• low density (15%): brain atrophy due to ischemia
• not visualized (10%)

CECT:

• tangle of intensely enhancing tubular structures = nidus ← tortuous dilated vessels (in 80%):
  • No avascular spaces within AVM
  • rapid shunting with veins seen during “arterial” phase
  • ± interspersed internal focal isoattenuating areas ← normal brain parenchyma (in diffuse subtype)
• lack of mass effect / edema (unless thrombosed / bleeding)
• No enhancement if thrombosed
• thickened arachnoid covering

MR:

• flow void ← rapid arteriovenous shunting (imaging with GRASS gradient echo + long TR sequences)
• 3-D TOF demonstrates feeding arteries + nidus + draining veins
  Pitfalls:
  1. signal void in tortuous vessels
  2. nonvisualization of draining veins resulting from spin saturation
  3. difficulty differentiating blood flow from blood clot

Angio:

• grossly dilated efferent + afferent vessels with a racemose tangle (“bag of worms”)
• arteriovenous shunting into at least one early draining vein
• negative angiogram ← compression by hematoma / thrombosis

Cx:

1. Hemorrhage (common): bleeding on venous side ← increased pressure / ruptured aneurysm (5%)
2. Infarction

Rx: embolization, stereotactic radiosurgery, microsurgery

Prognosis: 10% mortality; 30% morbidity

Risk of hemorrhage: lifelong; increasing yearly by 2–4%; increasing to 6% in year following 1^st bleed + 25% in year following 2^nd bleed

DDx: glioblastoma with AV shunting, dural AV fistula, cerebral proliferative angiopathy