Cerebral arteriovenous malformation

Cerebral arteriovenous malformations (CAVMs), also known as classic brain AVMs, are a common form of cerebral vascular malformation and are composed of a nidus of vessels through which arteriovenous shunting occurs.

This article corresponds to the classic form of arteriovenous malformation involving the brain parenchyma, which is also referred as a pial arteriovenous malformation, once it is related to the pial vessels 6.

These malformations are characterized by a nidus forming the transition between the feeding artery and draining vein. When this transition is made directly then it is a fistula, i.e. a separate cerebral vascular malformation (e.g. brain / pial arteriovenous fistula).

Although arteriovenous malformations are thought to represent a congenital abnormality, they are thought to develop over time and are rarely found incidentally in the very young. Despite this, a third of AVMs which are diagnosed due to hemorrhage are identified before the age of 20 years 7. Overall, AVMs are diagnosed at a mean age of 31 years 8.

Overall, AVMs are thought to occur in approximately 4% of the population but become symptomatic in only 12% of affected individuals 8. There is no gender predilection 8.

Arteriovenous malformations tend to be solitary in the vast majority of cases (>95%). When multiple, syndromic associations must be considered, including:

CAVMs are the most common symptomatic vascular malformations. Possible presentations include 3:

  • incidental finding in asymptomatic patients: 15% 5
  • seizures: 20%
  • headaches
  • ischemic events due to vascular steal from normal brain
  • hemorrhage: 65% 5, incidence 2-3% per year 3
    • parenchymal
    • subarachnoid
    • intraventricular

The origin of arteriovenous malformations remains uncertain, although they are thought to be congenital 3, and perhaps involves dysregulation of vascular endothelium growth factor (VEGF) 1.

AVMs comprise a number of components:

  • feeding arteries
  • nidus (Latin for "nest")
    • shunting arterioles: the true culprit
    • interconnected venous loops
  • draining veins

The nidus is fed by one or more arteries and drained by one or more veins. The feeding arteries are enlarged due to the increased flow, and flow-related arterial aneurysms are encountered 3. Venous aneurysms also referred to as venous pouches, are seen as well. It may contain dystrophic calcification, a small amount of gliotic tissue, and blood at different stages of aging.

  • Supratentorial: ~85%
    • Superficial (two-thirds)
    • Deep (one-third)
  • Infratentorial: ~15%
  • Solitary AVMs (98%)
  • Multiple AVMs (2%)
    • associated with syndromes.
  • flow-related angiopathy secondary to endothelial hyperplasia
  • flow-related aneurysm
    • intranidal: located in the nidus
    • intrapedicular: located in the feeding vessel
  • remote aneurysm: haemodynamically unrelated to malformation

Brain AVMs can be divided into two types 4,6:

  • Compact (or glomerular) nidus: abnormal vessels without any interposed normal brain tissue. More common than diffuse nidus type.
  • Diffuse (or proliferative) nidus: no well-formed nidus is present, with functional neuronal tissue interspersed amongst the anomalous vessels.

The Spetzler-Martin AVM grading system relates morphology and location to the risk of surgery.

Diagnosis can be difficult on non-contrast CT. The nidus is blood density and therefore usually somewhat hyperdense compared to adjacent brain. Enlarged draining veins may be seen. Although they might be very large in size, they do not cause any mass effect unless they bleed.

Following contrast administration, and especially with CTA, the diagnosis is usually self-evident, with feeding arteries, draining veins, and intervening nidus visible in the so-called "bag of worms" appearance. The exact anatomy of feeding vessels and draining veins can be difficult to delineate, and thus, angiography remains necessary.

Remains the gold standard, able to exquisitely delineate the location and number of feeding vessels and the pattern of drainage. Ideally, angiography is performed in a bi-plane system with a high rate of acquisition, as shunting can be very rapid.

On angiography, an AVM appears as a tightly packed mass of enlarged feeding arteries that supply a central nidus. One or more dilated veins drain the nidus and abnormal opacification of veins occurs in the arterial phase (early venous drainage), represents shunting.

Fast flow generates flow voids, easily seen on T2 weighted images. Complications, including previous hemorrhage and adjacent edema, may be evident.

  • MRA: phase-contrast MR angiography is often useful for subtracting the hematoma components when an AVM complicated by an acute hemorrhage needs to be imaged.

Radiology report should include certain key points that help the clinician in deciding the management.  Radiological evidence of previous hemorrhage, intranidal aneurysm, ectasia or stenosis of draining vein, single draining vein or deep draining vein or deep or posterior fossa location of AVM are associated with a high risk of future hemorrhage.6

Risk of non-hemorrhagic complications like focal neurological deficit increases with a long pial course of draining vein, arterial steal, mass effect of AVM like hydrocephalus and with perinidal gliosis.6

Treatment options and rate of complications are dictated in part by the Spetzler-Martin grade. In general, the three options available are:

  1. microsurgical resection
  2. endovascular occlusion
  3. radiosurgery

Occasionally, AVMs have been known to spontaneously resolve 2, usually in the setting of intracranial hemorrhage, resulting presumably in venous compression and thrombosis. The annual risk of hemorrhage for an untreated AVM is 2-3%, resulting from a flow-related aneurysm, intra-nidal aneurysm, or venous thrombosis (rarely).

Following hemorrhage, the risk of a further bleed in the next 12 months is up to 18% 5.

Imaging differential considerations include:

Article information

rID: 6657
Synonyms or Alternate Spellings:
  • Classic brain arteriovenous malformation
  • Cerebral AVM
  • CAVM
  • Cerebral arteriovenous malformation (CAVM)
  • Cerebral arteriovenous malformations
  • Cerebral arteriovenous malformations (CAVM)'s
  • Cerebral AVM's
  • CAVM's
  • Pial arteriovenous malformation
  • Classic brain AVMs

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Cases and figures

  • Case 1: T1 C+
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  • Case 3: T2
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  • Case 3: angiography
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  • Case 5: thalamic AVM
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  • Case 6: cerebral arteriovenous malformation
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  • AVM
    Case 7: CT
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    Case 7: angiography
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  • Case 16: SWI
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  • Case 22: supraseller AVM
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  • Case 25: temporal lobe
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