Arteriovenous Malformations

Diseases,

Findings on Investigations:

CT:

  • Tangle of blood vessels: Serpentine or punctate high density on noncontrast
  • Enhance with contrast
  • Calcification may occur, hemorrhage may occur
  • Hydrocephalus may occur with Vein of Galen malformation

CTA:

  • Arteries & draining veins are visible well, but angiography is still necessary

MRI:

  • Localises the lesion well.
  • T1: curvilinear vessels
  • T2: curvilinear Signal voids indicate the patent vessels, no intervening brain tissue
  • FLAIR: vascular flow voids & high signal surrounding gliosis
  • Gradient echo GRE: assess for hemorrhage, hypointense
  • Strong enhancement
  • False negatives if small

MRA:

  • Useful but doesn’t show detailed architecture AVM

Catheter Angiogram:

  • Gold standard test
  • Useful for mapping of AVM, use selective catheterisation of 4 vessels, +external carotid arteries
  • Cardinal features:
    • Enlarged arteries, 1 or more. With or without feeding artery aneurysms.
    • Nidus, with or without intra-nidal aneurysms
    • Draining vein, 1 or more early draining vein
  • Arteries: May have associated aneurysm: Cortical “pial” supply (supplied by arteries that would normally supply brain tissue i.e. branches of circle of Willis). Much more rarely, dural supply (rare supply from arteris that normally supply dura)
  • Nidus= core= a cluster of entangled blood vessels this drains into the enlarged veins. May have associated aneurysm
  • Draining veins: These are early draining veins (i.e. present on arterial phase). They may be deep or superficial drainange.
  • Associated features: Aneurysm of the feeding artery (pedicle) may be present. Aneurysm of the nidus intranidal aneurysm may be present

Pathology:

  • Gross: tangled mass of blood vessels, wedge shaped
  • Microscopy: thick walled arteries (elastic stains), thick walled veins (arterialised), +/-thrombosis +/-recanalisation, gliosis between blood vessels.
  • Perinidal capillary network= Abnormal large capillaries in 1-7mm surrounding the nidus.

Classification:

Spetzler Martin Grading 1-5 system for surgical difficulty:

Size:

  • <3cm, score =1
  • 3-6cm, score =2
  • >6cm, score =3

Location:

  • Non-Eloquent, score =0
  • Eloquent, score =1

Deep drainage:

  • No, score =0
  • Yes, score =1

Treatment:

Options:

  • Observation: this is the best approach for unruptured AVMs
  • Surgery: Excision en bloc resection +ligation of feeding vessels
  • Endovascular Emoblisation to reduce size to allow radiosurgery, to reduce flow to allow surgical resection or rare to cure very small AVMs.
  • Gamma radiotherapy (stereotactic radiosurgery STRS)
  • Annualized rupture rate 2.1% per year [Based on ARUBA trial]

For ruptured AVMs consider treatment:

  • Grade 1 & 2: surgery
  • Grade 3: surgery or radiosurgery +embolization
  • Grade 4 & 5: multidisciplinary, usually conservative management for grade 5

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