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Brain, Venous Vascular Malformations

Andrew L Wagner, MD, Assistant Professor of Radiology, Instructional Faculty, University of Virginia School of Medicine; Director of Neuroradiology, Department of Radiology, Rockingham Memorial Hospital
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Updated: Aug 21, 2002

Introduction

Background

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.

Commonly called venous angiomas for many years, the term developmental venous anomaly has been advocated as a more appropriate term because the entity does not consist of abnormally formed vessels; it may be merely a dilation of existing pathways. DVAs provide normal venous drainage for a section of brain and removal or thrombosis results in venous infarction and/or hemorrhage in that area. Most cases are found incidentally and although isolated reports of hemorrhage associated with a DVA exist, the incidence of associated symptoms is extremely low.

Although some articles have espoused surgical treatment for this entity, this opinion is not widespread because the risk of causing an iatrogenic venous infarct appears to far exceed the risk of the lesion causing irreversible damage during the patient's lifetime. In fact, most cases of symptomatic DVAs occur when an associated cavernous angioma is present; this observation raises the possibility that the symptoms are actually caused by the cavernoma.

DVAs are associated with the other CNS vascular malformations (eg, arteriovenous malformation [AVM], cavernous malformation, capillary telangiectasia) in approximately 15-30% of patients, although it most frequently occurs in conjunction with cavernous angiomas. The association is so common that the presence of a DVA on an image should prompt a search for a more clinically important cavernoma. DVAs are also associated with head and neck venous malformations and hemangiomas.

Pathophysiology

DVAs consist of a fine network of enlarged medullary venules that join to drain into a central venous outflow track that then drains into the superficial or deep venous system, depending on the location of the malformation (see Image 1, Image 6). They likely result from the absence of normal venous drainage, which forces the venous outflow to find an alternative course.

The veins are typically separated by normal brain parenchyma and are physiologically normal, unlike the vessels in the other 3 CNS vascular malformations; however, distal stenoses can occasionally occur. When a stenosis is present, it may result in venous hypertension and conceivably may induce rupture of the tiny medullary veins that form the base of the lesion. Nussbaum et al (1998) have suggested that such venous hypertension may induce the formation of true AVMs.

DVAs are characteristically found along the lateral ventricles, draining into a subependymal or cortical vein. However, they may occur throughout the brain and some have suggested that they occur within the cord as well. When they are in the posterior fossa, the drainage can occur via a variety of routes, although Damiano et al (1994) reported that most drain to the veins of the lateral recess of the fourth ventricle, the precentral veins, the longitudinal intrategmental vein, or a transpontine vein.

Frequency

United States

DVAs occur in approximately 2% of the population.

International

DVAs occur in approximately 2% of the population.

Mortality/Morbidity

Although almost all DVAs are incidentally found and never cause clinical symptoms, sporadic reports of hemorrhage, seizure, and infarcts due to spontaneous thrombosis exist.

• Although hemorrhage is the most common clinical symptom associated with DVAs, the number of cases that actually represent hemorrhage from an associated cavernous malformation is unclear. Certainly, increased flow through the thin medullary veins that form the substance of the malformation can result in hemorrhage but this appears to be rare. Before a hemorrhage is attributed to a DVA, signs of an accompanying cavernoma must be carefully sought.
• Thrombosis of a DVA appears to result in the worst complications; a venous infarct often ensues as it causes blockage of the normal venous drainage in that area. Hemorrhage may occur if the DVA is then recanalized.
• Although seizures have often been associated with DVAs, to the author's knowledge, no scientific proof exists that these lesions are directly responsible for seizures. Striano et al (2000) reported findings in 1020 epileptic patients examined at their institution. Among the patients, only 4 (0.39%) had DVA at imaging; this rate is less than that reported in the general population.

Race

No known race predilection exists.

Sex

Gender differences in the incidence of DVAs have not been reported.

Age

Because they are thought to be congenital, DVAs can occur in persons of any age. Most often they occur in adults, likely because adults undergo MRI examinations more frequently than pediatric patients.

Anatomy

See Pathophysiology.

Presentation

Clinical symptoms in DVAs are thought to be uncommon. Although headaches and dizziness have been associated with DVAs, confidently attributing such generalized symptoms to this common lesion is difficult. Most cases with symptoms that are directly related to a DVA involve a DVA thrombosis and/or adjacent hemorrhage.

While some believe that DVAs can hemorrhage on their own, most notably after venous infarct in cases of spontaneous DVA thrombosis, most instances of hemorrhages with DVAs have been in patients with combined vascular malformations. Most likely, in the vast majority of these cases, the hemorrhage originated from the accompanying vascular malformation rather than from the DVA.

Preferred Examination

Although contrast-enhanced CT and nonenhanced 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 (see Images 1-2).

Limitations of Techniques

Although standard contrast-enhanced MRI is excellent in depicting DVAs, without the use of gradient-echo or echo-planar imaging adjacent hemosiderin from associated cavernomas may not be appreciated, especially with fast spin-echo techniques.

Differential Diagnoses

Brain, Arteriovenous Malformation
Brain, Capillary Telangiectasia
Brain, Cavernous Angiomas
Brain, MRI Appearance of Hemorrhage
Brain, Stroke

References

• Brain, Arteriovenous Malformation
• Brain, Capillary Telangiectasia
• Brain, Cavernous Angiomas
• Brain, MRI Appearance of Hemorrhage
• Brain, Stroke