Like aneurysms, AVMs are usually congenital and may be familial. Symptoms typically develop before age 30 with a slight male preponderance, and 6% of patients also have an intracranial aneurysm. Intracranial hemorrhage with or without subarachnoid hemorrhage is the initial presentation in half of the cases. In contrast to patients with saccular aneurysms, those with AVMs are much more likely to become symptomatic before a hemorrhage occurs (Fig 14-18). Seizures are the first manifestation in 30% of affected patients, whereas 20% have headaches or other focal neurologic deficits initially. The neurologic symptoms may be progressive or transient.
Of the 90% of AVMs that are supratentorial, about 70% are cortical and 20% are deep. The remaining 10% are located in the posterior fossa or dura mater. Early mortality occurs in up to 20% of cases when bleeding takes place, and the rebleeding rate is 2.5% each year. Most AVMs bleed into the brain, producing headaches and focal neurologic deficits.
The neuro-ophthalmic manifestations of an AVM depend on its location. Cortical AVMs in the occipital lobe may produce visual symptoms and headaches that resemble migraine. The visual phenomena are usually brief and unformed, but typical migrainous scintillating scotomata may, rarely, occur (see Chapter 12, Fig 12-2). Hemispheric AVMs may produce homonymous visual field defects. Signs and symptoms of brainstem AVMs are not specific and may include diplopia, nystagmus, dizziness, ocular motor nerve palsy, gaze palsy, anisocoria, or pupillary light–near dissociation. Reports of transient monocular visual loss caused by a steal phenomenon from an intracranial AVM are rare.
Some patients with AVMs report a subjective intracranial bruit, and occasionally the examiner will detect a bruit with auscultation of the skull over the AVM.
Abnormal arterial communication with one of the dural venous sinuses (dural AVM) results in elevated venous pressure and in turn increased intracranial pressure. Dural AVMs account for 10%–15% of intracranial AVMs. Patients often have tinnitus and an audible bruit in addition to signs and symptoms of increased intracranial pressure. Dural AVMs are difficult to diagnose without catheter angiography and may be mistaken for typical idiopathic intracranial hypertension (IIH) (see Chapter 4). Dural AVMs should be considered in the patient who does not fit the usual IIH demographics and who has no other demonstrable cause of increased intracranial pressure.