When hemorrhage occurs from an AVM, it is typically in the form of an intracerebral lesion causing a hemiparesis, hemiplegia, and so forth, or even death. Blood may enter the subarachnoid space, producing a picture almost identical to that of a ruptured saccular aneurysm, but generally less severe. AVMs are about one-tenth as common as saccular aneurysms and about equally frequent in males and females. The two lesions—AVM and saccular aneurysm (on the main feeding artery of the AVM)—are associated in approximately 5 percent of cases; the conjunction increases with the size of the AVM and the age of the patient (Miyasaka et al). AVMs rarely occur in more than one member of a family in the same generation or successive ones. For a review of the embryologic theories of formation of AVMs, the reader is directed to the article by Fleetwood and Steinberg. However, Nikolaev and colleagues found somatic (not germline) mutations in KRAS in endothelial cells within the malformation in about half of their patient’s specimens and some evidence of upregulation of angiogenesis as a result.
Bleeding or seizures are the main modes of presentation. Most AVMs are clinically silent for a long time. Although the lesion is present from birth, onset of symptoms is most common between 10 and 30 years of age; occasionally it is delayed to age 50 or even beyond. In almost half of patients, the first clinical manifestation is a cerebral subarachnoid hemorrhage; in 30 percent, a seizure is the first and only manifestation; and in 20 percent, the only symptom is headache. Progressive hemiparesis or other focal neurologic deficit is present in approximately 10 percent of patients. The first hemorrhage may be fatal, but in more than 90 percent of cases the bleeding stops and the patient survives. Most often there are no symptoms before rupture. Chronic, recurrent headache may be a complaint; usually it is of a nondescript type but a classic migraine with or without neurologic accompaniment occurs in approximately 10 percent of patients—probably with greater frequency than it does in the general population. Most of the malformations associated with migraine-like headaches lie in the parietooccipital region of one cerebral hemisphere, and about two-thirds of such patients have a family history of migraine.
Huge AVMs may produce a slowly progressive neurologic deficit because of compression of neighboring structures by the enlarging mass of vessels and by shunting of blood through greatly dilated vascular channels. It has also been proposed that an “intracerebral steal” can result in hypoperfusion of the surrounding brain (Homan et al). When the vein of Galen is enlarged as a result of drainage from an adjacent AVM, hydrocephalus may result, particularly in children. With moderate size and large lesions, one or both carotid arteries frequently pulsate unusually forcefully in the neck. A systolic bruit heard over the carotid in the neck or over the mastoid process or the eyeballs in a young adult is suggestive of an AVM. However, such bruits have been heard in fewer than 25 percent of our patients. Exercise such as repeated squatting that increases the pulse pressure may bring out a bruit if none is present at rest. There is no relation of the existence of an AVM, or its rupture, to chronic hypertension (the same pertains to cerebral aneurysms).
Inspection of the eye grounds will rarely disclose a retinal vascular malformation that is coextensive with a similar lesion of the optic nerve and basal portions of the brain. Cutaneous, orbital, and nasopharyngeal AVMs may occasionally be found in relation to a cerebral lesion. Skull films rarely show crescentic linear calcifications in the larger malformations.