Overview
Arterio-venous malformations represent anomalous connections between arteries and veins through a disorganised tangle of small vessels called nidus and are a circulation wherein blood bypasses the capillaries and goes directly from arteries to veins.
Clinical features(1)
Usually arterio-venous malformations are asymptomatic; however they may present with headache,
numbness,
weakness etc.
depending on their location and extent of bleeding.
In patients who present without haemorrhage,
clinical presentations include:
- Seizures
- Headache
- Muscle weakness or numbness
Depending on the location of the AVMs,
patients can have more serious clinical presentations including:
- Severe headache
- Weakness,
numbness or paralysis
- Vision loss
- Difficulty speaking
- Confusion
- Unsteadiness
Risk factors
- Male gender
- Family history of AVMs
- Syndromic associations such as Hereditary haemorrhagic telangiectasia and Wyburg-Mason syndrome
Imaging findings
CT: A hyperdense nidus is seen on non-contrast CT.
On CECT,
feeding arteries,
early draining vein and a nidus with a "bag-of-worms" appearance is seen.
Digital subtraction angiography: Gold standard investigation which shows a tightly packed area of enlarged feeding vessels,
a nidus and early draining vein.
MRI: T2 weighted images show prominent flow voids.
In the presence of haemorrhage and surrounding oedema,
characteristic appearane depending on the age of the haemorrhage with surrounding high T2 signal (oedema) is seen.
Grading of intracranial AVMs - Spetzler-Martin grading system(2)
Described to predict operative outcome,
this grading gives a score of 1 to 5 based on different parameters while a score of 6 is given for inoperable lesions.
CHARACTERISTIC
|
NO.
OF POINTS ASSIGNED |
SIZE OF AVM
- Small (<3 cm)
- Medium (3-6 cm)
- Large (>6 cm)
|
1 point
2 points
3 points
|
LOCATION
- Non-eloquent site
- Eloquent site
|
0 point
1 point
|
PATTERN OF VENOUS DRAINAGE
- Superficial only
- Deep component
|
0 point
1 point
|
Eloquent sites include Sensorimotor,
language,
visual cortex,
hypothalamus,
thalamus,
internal capsule,
brainstem,
cerebellar peduncles,
or cerebellar nuclei.
Spinal arteriovenous malformations can be classified as:
- intramedullary
- extramedullary: 80%(3)
Or into four types(4):
- type I: Dural AV fistula - single coiled vessel
- type II: intramedullary glomus AVM
- type III: juvenile
- type IV: intradural perimedullary (AV fistula)
Complications
Haemorrhage - Intraparenchymal,
subarachnoid etc.
Aneurysm formation
Hydrocephalus due to obstruction to CSF absorption
Cerebral atrophy
Myelopathy from venous congestion
Hemorrhage within the cord parenchyma or subarachnoid space(5)
Arterial steal from adjacent spinal cord segments - high flow AVMs.
Treatment
Microsurgical resection
Endovascular occlusion
Radiosurgery