Vascular Malformations of the Brain

• Arteriovenous malformation (shown above): Feeding arteries, draining veins, and intervening nidus of abnormal vessels. Frequently diagnosed after hemorrhage. CT may show high-attenuation and enhancing serpentine structures corresponding to enlarged, tortuous vessels. Focal calcification and lack of mass effect are characteristic. MRI will show flow voids and evidence of hemoglobin breakdown. Perilesion gliosis appears as T2-hyperintensity. Angiography is the gold standard for excluding an arteriovenous malformation and for assessing the size of the nidus. The patient shown above presented with cerebellar hemorrhage. MRI showed heterogeneous T1 and T2 signal due to hemorrhage associated with hemosiderin deposition. Angiography reveals vessels from branches of the left superior cerebellar artery and left posterior inferior cerebellar artery (pink and blue arrows, respectively) feeding a nidus (white arrow), and draining into the transverse sinus (green arrow). The superior cerebellar artery is displaced superiorly by the cerebellar hemorrhage.
• Dural arteriovenous fistula: Arteriovenous fistula in the meninges supplied partly or wholly by dural arteries and drained by dural sinuses and/or leptomeningeal venous channels. They most frequently involve the cavernous or transverse/sigmoid sinuses. CTA may show dilated cortical or subcortical vessels. May be complicated by hemorrhage, in which case there will be parenchymal hematoma with or without subarachnoid blood. The pattern may simulate a hemorrhagic venous infarction (look for a thrombosed venous sinus). Contrast-enhanced MRI and MRA is the best noninvasive modality, but angiography is the gold standard.
• Cavernous angioma: Well-demarcated, high-attenuation lesion on CT due to hemorrhage or calcification. Contrast enhancement is inconsistently seen. Heterogeneous T1 and T2 signal consistent with subacute hemorrhage. Hemosiderin rin ("black halo") typical. Gradient-echo good for detecting small lesions. Differentiated from hemorrhagic tumor by absence of surrounding vasogenic edema. Usually not seen on angiography (used to be called "occult arteriovenous malformations").
• Developmental venous anomaly: Also known as venous angioma and medullary venous malformation. Purely venous anomaly. CT may reveal calcifications if associated with a cavernous angioma (see above). Acute parenchymal hemorrhage is rare. CTA reveals numerous linear or dot-like foci of enhancement that converge on an enlarged tubular draining vein (Medusa head). T1-weighted images can be be normal in small anomalies. Flow voids may be seen on T1- and T2-weighted images. Contrast-enhanced images reveal similar findings as CTA. MRV will help show the drainage pattern of the draining vein.
• Capillary telangiectasia: Small, abnormally dilated capillaries within otherwise normal brain tissue. Presence of normal brain tissue between the capillaries distinguishes it from cavernous angioma pathologically. Most commonly occur in the pons. Usually not visible on CT (even post-contrast). On MRI, there is lacelike and subtle enhancement with little or no signal abnormality on T2-weighted images. They may be hypointense or isointense on T1-weighted images. There is signal loss on gradient echo sequences.

References

Byrne JV. Cerebrovascular malformations. Eur Radiol. 2005 Mar;15(3):448-52.