Arteriovenous Malformation:
Arteriovenous malformations consist of feeding arteries that are dilated with a cluster of entangled vascular loops. Blood flows preferentially through the AVM therefore depriving other areas of the brain of blood flow. This steal phenomenon can produce neurological symptoms, seizures, and parenchymal loss. This increase in blood flow also can produce aneurysms. The location of the AVMs is 80-85% in the cerebral hemispheres and 10-15% in the posterior fossa.

Clinical Presentation:
Arteriovenous malformations are usually congenital developmental anomalies, but are frequently asymptomatic until 30 to 40 years of age. Approximately 25% of these patients hemorrhage by age 15 and 80-90% of the patients are symptomatic by age 50. Symptoms include seizure and headaches.

Pathology:
Arteriovenous malformations consist of feeding arteries that are dilated with a cluster of entangled vascular loops. Blood flows preferentially through the AVM therefore depriving other areas of the brain of blood flow. This steal phenomenon can produce neurological symptoms, seizures, and parenchymal loss. This increase in blood flow also can produce aneurysms. The location of the AVMs is 80-85% in the cerebral hemispheres and 10-15% in the posterior fossa.

Image Findings:
CT scans typically show tangled vessels in the parenchyma that are high density contrast. These vessels are noted to have a serpentine configuration. Curvilinear or speckled calcification may also be present. MR scans show curvilinear flow voids secondary to fast flow seen on pulse sequences and dilated feeding arteries. The appearance of the arteries vary due to flow rate, direction, pulse sequence, and the presence and age of the hemorrhage. Gliosis and hemorrhages also appear on the MR images. Often MRA images are used to diagnose the disease. MR is more sensitive to the feeding arteries, the core or nidus, and the enlarged draining veins.

Differential Diagnosis:
Differential diagnosis includes vascular malformations. If normal blood flow is present, capillary telangiectasis and developmental venous anomalies are commonly confused with AVM. Capillary telangiectasis are lesions measuring approximately 3 cm in diameter and are typically found in the pons. The majority of the lesions do not hemorrhage and are observed as nodular enhancements after contrast on T1WI. Developmental venous anomalies are the most common cerebral vascular malformation. These malformations rarely hemorrhage. If hemorrhage is noted, it is most likely due to a coexisting cavernous angioma. If the malformation is isolated, they appear to be composed of dilated medullary veins that form a large channel draining into cortical veins or subependymal veins. If there is high blood flow, AV fistula shares similar characteristics with AVM. AV fistula is an arterial dissection or laceration that spontaneously communicates with an adjacent vein or dural sinus. These fistulas are commonly seen in the cavernous sinus, below the petrous temporal bone, and foramen magnum.

Treatment:
Depending on the size and location of the AVM, the treatment may include embolization, surgery, or radiation therapy.