Also known as Developmental venous anomaly (DVA).
Congenital malformation of veins which drain normal brain. They were thought to be rare before cross-sectional imaging but are now recognised as being the most common cerebral vascular malformation, accounting for ~55% of all such lesions.
A VA is characterised by the caput medusae sign of veins draining into a single larger collecting vein, which in turn drains into either a dural sinus or into a deep ependymal vein. The appearance has also been likened to a palm tree.
The aetiology of VAs remains uncertain, but may relate to arrested development of venous structures
Histologically they consist of a number of abnormally thickened veins with normal feeding arteries and capillaries
The most common locations are:
frontoparietal region (36-64%) 1, usually draining towards the frontal horn of the lateral ventricle
cerebellar hemisphere (14-27%) draining towards the fourth ventricle
However, DVAs can be seen anywhere, draining either superficially or deep.
Lesions are usually solitary (75%) 2, except in blue rubber bleb naevus syndrome
~20% (range 8-33%) of cases 2 are associated with cavernous malformations and are referred to as mixed vascular malformations (MVM) there is an association with venous malformations of the head and neck 2
VAs are seen on both CT and MRI as a leash of vessels draining towards a central vein.
If large, the draining vein may be seen on non-contrast CT, and is confirmed with contrast administration as a linear or curvilinear enhancing structure.
May be visible on most sequences, but is most easily seen on postcontrast T1 sequences. If there is an associated cavernous haemangioma then susceptibility weighted sequences will be most sensitive for this component.
SWI is the preferred sequence in venous anomalies and proved to have better detectability of venous structures than conventional T2*-weighted imaging. Signals on SWI are not compromised by low-velocity venous flow. Therefore, SWI has successfully demonstrated low-flow vascular formations such as DVA. DSA: angiography
Angiographically the caput medusae appearance (collection of dilated medullary veins converge in an enlarged transcortical or subependymal collector vein) is pathognomonic and seen only in the venous phase. Arterial phase appears normal although late capillary blush may be present. No shunting is present. Treatment and prognosis
If isolated, than no treatment is necessary. If part of an MVM then treatment will be predicated by the other component. Informing the surgeon of the presence of a DVA is however essential as cautery of the the collecting vein can lead to venous infarction.
When isolated, a DVA has a very low complication rate (0.15% per annum) mainly from spontaneous thrombosis of the collecting vein leading to venous infarction and haemorrhage.
However, DVAs are commonly associated (15-20%) with other vascular malformations, most commonly a cavernous malformation in which case they should be referred to as mixed vascular malformations. Their risk of complication is then elevated to that of the associated lesion. There is an association with cortical dysplasia 7.
A more recent study has demonstrated that in exceedingly rare cases, the DVA can become symptomatic by various vascular complications. The authors suggested identification of the underlying pathomechanism by MR and DSA for proper management. Importance of preserved integrity of the DVA itself still holds true 6. Differential diagnosis
General imaging differential considerations include:
Dural sinus thrombosis with collateral drainage
Sturge Weber syndrome with leptomeningeal angiomatosis
demyelination may also have enlarged medullary veins
Think of an associated cavernoma when a DVA is found in an intraparenchymal hemorrhage investigation (DVA rarely bleed)
Best options to find it could be a gradient-echo or blood oxygen level-dependent sequences on MRI 1)