Vascular malformations of the brain can be organized into five subtypes: (1) cavernous malformations, (2) capillary telangiectasias, (3) arteriovenous malformations (AVMs), (4) developmental venous anomalies, and (5) dural arteriovenous fistulas (dAVFs). Vascular malformations most often come to clinical attention when they cause intracerebral hemorrhage. Occasionally, they may be found in patients with epilepsy as a seizure focus. Increasingly, vascular malformations are discovered incidentally on brain imaging performed to evaluate an unrelated neurologic complaint. In patients with vascular malformations, the most important driver of treatment decisions is whether or not the lesion is symptomatic.
Cavernous malformations, or cavernomas, are thin-walled venous cavities that can be found in the cortex, white matter, basal ganglia, brainstem, and spinal cord. They are usually sporadic, but familial syndromes associated with multiple cavernomas exist and are important to recognize. Cavernomas are angiographically occult, and vascular imaging is not indicated. Bleeding risk is increased in patients with prior hemorrhage or focal neurologic deficits attributed to cavernoma and in those with brainstem cavernoma location. For example, in patients with asymptomatic, incidentally discovered non-brainstem cavernomas, the risk of bleeding is < 1% per year, increasing to 3%–4% per year in patients with prior hemorrhage and non-brainstem cavernomas, and as high as 5%–6% per year in those with brainstem cavernoma with prior hemorrhage. Surgical resection of a cavernoma should be considered in patients with recurrent hemorrhage or intractable epilepsy, particularly if easily accessible surgically. Resection is generally not performed after a single hemorrhage in isolation.
Capillary telangiectasias are small clustered capillary-like anomalies usually found in the brainstem and cerebellum. They are most often incidental imaging findings and do not require monitoring or further investigation except when part of a genetic disorder such as hereditary hemorrhagic telangiectasia. Symptomatic hemorrhage is extremely unusual.
AVMs are tortuous collections of histologically abnormal vessels that are supplied by feeding arteries and drain into deep or superficial veins. Their lack of an organized capillary network can cause high-flow arteriovenous shunting of blood. The most feared complication is intracranial hemorrhage, which can be subarachnoid, from an associated feeding artery aneurysm, or intraparenchymal, from intranidal rupture. Bleeding risk is increased with prior hemorrhage, deep location, deep venous drainage pattern, and if an associated aneurysm is present. In patients with prior hemorrhage, annual risk of recurrent bleeding is ~ 5%. Seizures and headache can also occur with AVMs. Catheter angiography is necessary to define AVM anatomy to guide treatment decisions. Given their complexity, evaluation and management of a ruptured AVM should be done by an experienced multidisciplinary team. Treatment options include endovascular embolization, radiosurgery, and surgical resection. Staged intervention is sometimes necessary.
Developmental venous anomalies are normal venous channels that have an anomalous location or radiographic appearance. While they can be very rarely associated with hemorrhage, especially when associated with a cavernoma, surgical intervention is almost always contraindicated because of their physiologic role in venous drainage of functional brain tissue; disturbance can lead to venous infarction and further hemorrhage.
A dAVF is a dural-based arteriovenous shunt, typically supplied by extracranial arterial branches that anastomose with an intracranial dural vein and sinus. A dAVF is typically acquired through trauma or aberrant revascularization after cerebral vein thrombosis. Cerebral dAVF may present with symptomatic intracranial hemorrhage, cerebral edema, seizure, or pulsatile tinnitus. One commonly encountered form of dAVF is cavernous-carotid fistula, which can present with local eye abnormalities such as scleral injection, proptosis, double vision, and visual blurring or loss of vision. Spinal dAVF may also occur, typically manifesting with progressive myelopathy. Catheter angiography is necessary for adequate diagnostic evaluation; note that dAVFs are often not well seen on noninvasive vascular imaging studies (computed tomography or magnetic resonance angiography). In general, symptomatic dAVFs should be treated, often requiring a multidisciplinary approach (endovascular embolization, open surgical resection, less commonly stereotactic radiosurgery). Lesions are classified based on location and involvement of cortical veins. The presence of cortical venous drainage carries an increased risk of hemorrhage, which typically justifies referral for intervention.