venerdì 9 febbraio 2007
Developmental venous anomaly
Initial noncontrast head CT (Figure 1) shows abnormal hyperdensities within the right Sylvian fissure and adjacent insular cortex, raising the possibility of a vascular malformation.
Follow-up T2-weighted MR image (Figure 2) shows multiple linear increased signal intensity foci in the deep white matter converging near the ventricular surface. These represent dilated medullary veins of the caput medusa.
Cerebral angiography during the arterial phase (Figure 3) is normal while the venous phase (Figure 4) shows umbrella-like medullary veins converging on two collector veins (red arrows in Figure 4) which then empty into a normal venous system.
Diagnosis: Developmental venous anomaly
Developmental venous anomaly (DVA), also known as venous malformation or venous angioma, refers to aberrant venous development and is composed of a network of dilated medullary veins converging in a radial or umbrella-like fashion onto a large collector vein. The collector vein follows an aberrant course to empty into normal superficial or deep veins. A DVA can occur in the cerebrum, cerebellum, or brainstem and is characterized by normal intervening parenchyma. As it is a normal variant, clinically significant hemorrhage is unusual and should raise the possibility of a concomitant cavernous angioma or other vascular malformation.
On CT, a small DVA may not be visualized; however, a large DVA may be seen as a hyperdense lesion.
Blood flow within DVAs is slow, which produces fluid-like signal intensity rather than flow void on MR imaging. Strong contrast enhancement is typical; the lack thereof should raise doubt about the diagnosis of DVA.
On cerebral angiography, the classic “Medusa head” appearance is visualized on the venous phase, with the arterial and capillary phases normal.