Cerebral arteriovenous malformations are the most common type of cerebrovascular malformation, formed by abnormal development of cerebral vessels during the embryonic period, and can vary widely in size, morphology, and tissue structure. The typical cerebral arteriovenous malformation consists morphologically of a blood supplying artery, an abnormal vascular mass, and a draining vein; in some cases, the artery communicates directly with the vein (fistula type) and the vasculature dilates abnormally at the fistula opening to form a tumor-like pattern. Small cerebral arteriovenous malformations may be unremarkable on cerebral angiography, while large ones may involve the entire cerebral hemisphere. There may be one or multiple supplying arteries, draining into superficial veins and deep veins. Some vascular clusters are dense; others are diffuse, with more brain tissue interspersed between the abnormal vessels. Clinical manifestations Hemorrhage: Hemorrhage is the most common clinical manifestation of cerebral arteriovenous malformations. Patients with large arteriovenous veins present with epilepsy earlier than hemorrhage, whereas the opposite is true for small-vessel malformations. It is generally believed that the higher incidence of hemorrhage in small-vessel malformations is due to the smaller number of draining veins in the donor artery phase. It has been hypothesized that fewer donor arteries/drainage veins may mean that there is a higher pressure within such a single donor artery or drainage vein, predisposing to hemorrhage. Intraoperative measurements of pressure in the supply artery have been made and found that the pressure in the small malformation supply artery was close to the mean arterial pressure; this speculation was confirmed by the fact that the pressure in the large malformation supply artery was significantly lower than the mean arterial pressure. Similarly, small vascular malformations involving fewer cortical areas are less likely to produce epilepsy, and hemorrhage becomes the only way to manifest symptoms. Hemorrhage is more often found in the deeper paraventricular part of the nidus, which may break into the ventricles, and also manifests as subdural or subarachnoid hemorrhage Epilepsy: is the second most common manifestation of cerebral arteriovenous malformations, occurring in 70% of patients with cerebral arteriovenous malformations. 25% of patients have epilepsy as the only symptom. Epilepsy due to cerebral arteriovenous malformation can be focal or generalized, or it may result from a small hemorrhage from the malformation. Large superficial malformations appear to be more likely to produce epilepsy than small deep malformations, which more often present as hemorrhages. Headache: Headache, unrelated to hemorrhage and epilepsy, is the third first symptom of cerebral arteriovenous malformations, ranging from 5% to 35%. With the widespread use of MRI, arteriovenous malformations can be precisely localized, their size can be determined and resected, and MRI can detect posthemorrhagic traces. Other manifestations: Cerebral arteriovenous malformations can present with progressive neurological deficits or a clinical course that resembles demyelinating lesions, often resulting in neurological syndromes due to high blood flow, high volume AV shunts that cause blood theft and ischemia. Hydrocephalus due to hemorrhage is also not uncommon. In children as a first symptom hemorrhage is 7 times more common than in epilepsy.