Cerebral arteriovenous malformation

A.Prof Frank Gaillard et al.

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 characterised 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 haemorrhage 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
  • ischaemic events due to vascular steal from normal brain
  • haemorrhage: 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 ageing.

Location
  • supratentorial: ~85%
    • superficial (two-thirds)
    • deep (one-third)
  • infratentorial: ~15%
Incidence
  • solitary AVMs (98%)
  • multiple AVMs (2%)
    • associated with syndromes
Associated abnormalities
  • 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
  • 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.

CT

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.

MRI

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

  • MRA: phase contrast MR angiography is often useful for subtracting the haematoma components when an AVM complicated by an acute haemorrhage needs to be imaged
Angiography (DSA)

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.

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 haemorrhage, resulting presumably in venous compression and thrombosis. The annual risk of haemorrhage for an untreated AVM is 2-3%, resulting from a flow-related aneurysm, intra-nidal aneurysm, or venous thrombosis (rarely).

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

Imaging differential considerations include:

Share article

Article information

rID: 6657
Section: Pathology
Synonyms or Alternate Spellings:
  • 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

Support Radiopaedia and see fewer ads

Cases and figures

  • Drag
    AVM T1 Gad
    Case 1: T1 C+
    Drag here to reorder.
  • Drag
    AVM
    Case 2
    Drag here to reorder.
  • Drag
    AVM T2
    Case 3: T2
    Drag here to reorder.
  • Drag
    AVM DSA
    Case 3: angiography
    Drag here to reorder.
  • Drag
    MIP (maximim inte...
    Case 4
    Drag here to reorder.
  • Drag
    Case 5: thalamic AVM
    Drag here to reorder.
  • Drag
    AVM
    Case 8: CT
    Drag here to reorder.
  • Drag
    Frontal projectio...
    Case 8: angiography
    Drag here to reorder.
  • Drag
    Case 9
    Drag here to reorder.
  • Drag
    Case 10
    Drag here to reorder.
  • Drag
    Case 11
    Drag here to reorder.
  • Drag
    Case 12
    Drag here to reorder.
  • Drag
    Case 13
    Drag here to reorder.
  • Drag
    Case 14
    Drag here to reorder.
  • Drag
    Case 15
    Drag here to reorder.
  • Drag
    Case 16
    Drag here to reorder.
  • Drag
    Case 17: SWI
    Drag here to reorder.
  • Drag
    Case 18
    Drag here to reorder.
  • Drag
    Case 19
    Drag here to reorder.
  • Drag
    Case 20
    Drag here to reorder.
  • Drag
    Case 21
    Drag here to reorder.
  • Drag
    Case 22
    Drag here to reorder.
  • Drag
    Case 23: supraseller AVM
    Drag here to reorder.
  • Drag
    Case 24
    Drag here to reorder.
  • Updating… Please wait.
    Loadinganimation

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.