Venous vascular malformations, also known as venous angiomas or, more properly, developmental venous anomalies (DVAs), represent congenital anatomically variant pathways in the normal venous drainage of an area of the brain. Once thought to be rare, they are now considered to be the most common vascular malformation in the CNS.
They may occur in as many as 2% of individuals. (See the images of venous vascular malformations below).
Although contrast-enhanced computed tomography (CT) scanning and nonenhanced magnetic resonance imaging (MRI) can reveal a DVA, the preferred imaging technique is contrast-enhanced MRI because of its excellent depiction of the small venules and draining vein. The multiplanar capabilities of MRI are especially useful because the typical configuration of a DVA is often best recognized in the coronal plane.
Although standard contrast-enhanced MRI is excellent in depicting DVAs, adjacent hemosiderin from associated cavernomas may not be appreciated without the use of gradient-echo or echo-planar imaging, especially with fast spin-echo techniques.
Brain, venous vascular malformation. Coronal T1-weighted contrast-enhanced image obtained in a patient who had undergone surgery in the past for an arteriovenous malformation (AVM) shows bilateral developmental venous anomalies (DVAs) and the classic caput medusa appearance. Note the signal intensity abnormality in the inferior right cerebellar hemisphere due to the prior surgery.
Brain, venous vascular malformation. Coronal T1 postcontrast demonstrates a typical location for a DVA, here within the periventricular white matter. This malformation drained into a cortical vein along the parietal convexity.
Brain, venous vascular malformation. Axial T2 image shows that the DVA can be subtle. In this patient, the draining vein is large enough to have a flow void on the image. The parenchymal abnormality is typically not visible.
Brain, venous vascular malformation. Axial fluid-attenuated inversion recovery shows some artifactual increased signal within the vessel, which can aid in detection of DVAs on noncontrasted studies.
Although for many years DVAs were commonly called venous angiomas, the newer term DVA has been recommended as more appropriate because the involved vessels are not abnormally formed, but apparently merely dilated. The majority of DVAs are found incidentally and never cause symptoms, although there are isolated reports of patients with syndromes attributed to DVAs (eg, secondary to hemorrhage or thrombosis).
The mechanisms of symptomatic DVAs are divided into mechanical (ie, hydrocephalus or nerve compression syndrome), flow-related causes, and idiopathic. Flow-related complications are divided into an increase in inflow and a decrease in outflow. In cases of increases in inflow, such as DVAs with arteriovenous shunts or arteriovenous malformations, patients may initially present with headache, neurologic deficit, seizures, and coma. Patients with a decrease in outflow are influenced by mechanical or functional causes. The mechanical causes include thrombosis of collecting veins (51.7%), stenosis of the DVA drainage pathway (24.1%), or complete thrombosis of DVA (24.2%).
While some believe that DVAs can hemorrhage on their own, most notably after venous infarction from spontaneous DVA thrombosis, most instances of hemorrhage with DVAs have been in patients with combined vascular malformations. In the vast majority of these cases, the hemorrhage probably originated from the accompanying vascular malformation rather than from the DVA.
Surgical treatment for DVAs has been advocated, but most experts believe that the resulting risk of an iatrogenic venous infarct would far exceed the risk of irreversible damage from the DVA itself during the patient’s lifetime. In fact, most patients with DVAs who become symptomatic have an associated cavernous angioma, which suggests that the symptoms are actually caused by the cavernoma. (See the image below.)
Brain, venous vascular malformation. Axial proton density–weighted image shows an area of marked signal intensity loss in the right cerebellum adjacent to the developmental venous anomaly (DVA). This finding is consistent with a coexistent cavernous angioma.
DVAs are associated with cavernous angiomas or one of the other types of CNS vascular malformations (ie, arteriovenous malformation [AVM], capillary telangiectasia) in approximately 15-30% of patients.
The most frequent conjunction is with cavernous angiomas; indeed, this association is so common that the two may be etiologically related,
and the presence of a DVA on an image should prompt a search for a cavernoma, which is more clinically important.
DVAs are also associated with head and neck venous malformations and hemangiomas. Rarely, DVAs are associated with varices.
Multiple imaging examples of parenchymal and perfusion abnormalities associated with DVAs have been documented.
Larvie et al reported that in a small series of 25 developmental venous anomalies, 72% were associated with the presence of a mild, moderate, or severe degree of DVA-associated hypometabolism (DVAAh).
In a follow-up study, 54% of DVAs were associated with a greater than 10% decrease in metabolic activity. The authors surmised that worsening of DVAAh with increasing age could imply that the natural history of DVAs may result in either increasing damage to adjacent brain parenchyma or possibly remodeling of parenchyma away from the region with altered venous drainage.