Arteriovenous Malformation

AVMs are congenital vascular anomalies characterized by a conglomeration of abnormal, dysplastic vessels forming a structure known as the “nidus.” These vessels are directly connected by a high-flow shunt between arterial feeders and venous drainers, bypassing the capillary system.

Most commonly diagnosed in young adults aged 20–40 years.

Congenital in origin and generally solitary in nature.

Location is predominantly supratentorial (85%) compared to the posterior fossa (15%).

Clinical Presentation

The 38-71% of patients present ICH. Other: focal or generalized seizures, headaches, focal or asymptomatic neurological deficits. The annual risk of hemorrhage is approximately 3%.

The Spetzler-Martin grading scale (tab. 1) estimates the risk of open neurosurgery by assessing the size of the AVM, the pattern of venous drainage, and its location (whether or not it affects eloquent areas).

Imaging findings

Non-contrast CT (NCCT)

- Iso-/hyperdense irregular vessels.

- Ca++ in 25-30% involving the nidus or draining veins.

- Presence of nidus (Fig. 2, 3).

- Encephalomalacia/gliosis of the surrounding brain parenchyma.

- In case of ICH, intraparenchymal and intraventricular hemorrhage >> subaracnoid hemorrhage.

CT angiography (CTA)

Feeding arteries, nidus and/or draining veins (Fig. 4).

MRI

T1, T2 - Nidus with hypo/hyperintense vessels and "honeycomb" morphology. - Absence of normal brain parenchyma in the nidus region.

T2* GRE - Signal drop (blooming) in case of hemorrhage.

FLAIR - Heterogeneous high surrounding signal (gliosis).

T1 C+ (contrast-enhanced T1) - Enhancement of nidus, draining veins.

MRA (Magnetic Resonance Angiography) - useful for general description of flow.

Dural arteriovenous fistula

Dural AVF represent a pathological anastomosis between the meningeal arteries and the dural venous sinuses or cortical veins. They are usually associated with chronic dural sinus thrombosis. They are distinguished from AVMs by their arterial supply from vessels that perfuse the dura mater and by the absence of a parenchymal nidus.

Represent 10 to 15% of all CVMs. Most of dural AVF appear in late adulthood (50-60 years) and are idiopathic. They are rarely the result of trauma, infection, tumors or thrombosis of the dural sinus.

Most common location - transverse and sigmoid sinus (Fig. 5).

Clinical Presentation

Posterior fossa - pulsatile tinnitus.

Cavernous sinus - pulsatile exophthalmos, neuropathy of III, IV, VI c.n., proptosis, chemosis and decreased visual acuity (Fig. 6).

Childhood AVF - developmental delay.

The Cognard classification (table 2) of dural AV fistulas is based on the type of venous drainage. Higher scores correlate with drainage into cortical veins and with a higher risk of hemorrhage.

Imaging findings

NCCT

- Hemorrhage and/or edema (due to venous hypertension).

- Enlarged transosseous vascular channels in the foramen spinosum (contains the middle meningeal artery that commonly supplies AVFs).

CTA

- Non-compact group of dilated or tortuous vessels without nidus

- Abnormal enhancement of the dural sinus due to early abnormal venous drainage.

MRI

T1, T2 - Isointense thrombosed dural sinus with flow voids.

FLAIR - Isointense thrombosed dural sinus with adjacent edema

T2* - Thrombosed dural sinus with blooming

T1 C+ - Chronically thrombosed sinus usually enhances

MRA, TOF MRA, MRV (MR venography) - useful for macroscopic depiction of angioarchitecture (Fig. 7, 8). Asymmetry with arterialization of the affected dural sinus (Fig. 9).

Vein of Galen aneurysmal malformation

VGAM is a vascular anomaly that corresponds to an arteriovenous fistula between the deep choroidal arteries and the embryonic median prosencephalic vein of Markowski. Represent <1% of cerebral vascular malformations, but up to 30% of pediatric vascular malformations.

The most common extracardiac cause of high-output heart failure in newborns. Without treatment, patients die from intractable heart failure and multisystem failure.

Imaging findings

NCCT

Slightly hyperdense median prosencephalic vein compared to the brain. Hydrocephalus. Hypodensity of the subcortical white matter and Ca++ due to chronic venous ischemia.

CTA

Vascular enhancement of the feeding arteries and the median prosencephalic vein. Delineates the feeding arteries, venous drainage.

MRI

T1, T2 - Absence of flow within the vein of Galen or its heterogeneity due to rapid or turbulent flow (Fig. 10).

DWI, ADC map - Diffusion restriction in case of acute ischemia/infarction.

MRA - Delineates the feeding arteries.

C+ MRA - Shows the arterial and venous anatomy together.

MRV - Delineates the vein of Galen and the venous anatomy.

Cavernous malformation

Synonyms: cavernous angioma, cavernous hemangioma or cavernoma. CM histologically is characterized by a lobulated group of dilated sinusoidal canals lined with endothelial cells. They are antigenically immature (lack muscular and elastic layers), present repeated intralesional hemorrhages and do not contain normal brain parenchyma.

Presentation at 30-40 years. Up to 1/4 of CMs are discovered in infancy and childhood.

Clinical Presentation

Headache or seizures / detected incidentally. Represent 10-15% of all CVMSs. Annual hemorrhage risk of 2,5%.

The Zabramski classification for cavernous angiomas (Table 3) predicts the occurrence of symptomatic intracerebral hemorrhage.

Imaging findings

NCCT

- Negative in 30-50%.

- Well-circumscribed round/ovoid hyperdense lesion <3cm - 40-60%Ca++.

- No mass effect (unless recent hemorrhage) or changes in surrounding brain (Fig. 11).

CTA

- Little/no enhancement unless mixed with another lesion (e.g. DVA).

MRI

T1, T2 - "Popcorn" of mixed hyper- and hypointense blood-containing stones (Fig. 12).

T2 - Peripheral hypointense hemosiderin rim.

FLAIR - May show surrounding edema in acute lesions.

T2*GRE - Prominent susceptibility effect ("hypointense blooming", Fig. 13). Multiple ACs - hypointense punctate foci ("black spots")

DWI - Susceptibility effects

T1 C+ - Minimal or no enhancement (may show associated DVA)

MRA - Normal (unless mixed malformation present).

Developmental venous anomaly

DVA, also known as venous angioma, is a congenital CVM with mature venous elements and normal interposed brain tissue. It consists of a fine network of white matter venules that flow into a large central vein, which drains into a dural sinus or a deep ependymal vein.

It is the most common CVM at autopsy (60% of the total). It has a prevalence of 2,5-9% in MRI scans with contrast.

Most frequent location - vicinity of frontal horns of the lateral ventricle. They are associated with other CVMs in 15-30%, predominantly with cavernous malformations.

Clinical Presentation

It is usually asymptomatic. Uncommon - headache, seizure (if associated with cortical dysplasia), hemorrhage with focal neurological deficit (if associated with cavernous angioma).

The annual risk of hemorrhage is very low - 0.15%.

Imaging findings

NCCT

- Often missed on baseline.

- Enlarged "collector" vein may appear hyperdense; possible pitfall with thrombosis/SAH.

- Ca++ if mixed cavernous malformation.

CTA

- Numerous linear or punctate enhancement foci converging on an enlarged tubular drainage vein.

MRI

T1, T2 - May be normal if DVA is small. Blood product flow voids (Fig. 14).

T1 C+ - Strong enhancement of multiple tubular emissary veins converging on the collector vein (medusa head image, Fig. 15).

MRA - Arterial phase is usually normal. MRV delineates the "medusa head" and drainage pattern.

Capillary telangiectasia

Also known as a capillary malformation, represents a group of enlarged, dilated, thin-walled capillaries separated by normal brain parenchyma. Accounts for 15-20% of all CVMSs.

Usually is found incidentally at autopsy or on imaging. Peak presentation at age 30-40 years. Most common location is pons and cerebellum.

Clinical Presentation

Clinically usually benign, inactive, unless histologically mixed with other vascular malformations. No hemorrhage unless another vascular malformation (e.g., CM) is present.

Imaging findings

NCCT and CTA

- Usually, normal.

- May occasionally show Ca++ if there is a mixed histology (most commonly associated with cavernous angioma).

MRI

T1 - Usually normal

T2 - 50% normal, 50% show a weak punctate focus of hyperintensity.

T1 C+   - Faint punctate or brush-like enhancement. May have an enlarged central drainage vein with prominent linear enhancement (Fig. 16, 17).

The table 4 summarizes differential diagnosis of the main CVMs.