Arteriovenous Malformations

Like aneurysms, AVMs are usually congenital and may be familial. Symptoms typically arise before 30 years of age, 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, patients with AVMs are much more likely to become symptomatic before a hemorrhage occurs (Fig 14-17). 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% of AVMs 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, causing headaches and focal neurologic deficits.

An AVM’s neuro-ophthalmic manifestations 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; typical migrainous scintillating scotomata may occur but are rare (see Chapter 12, Fig 12-1). 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 via 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 IIH (see Chapter 4). Dural AVMs should be considered if the patient does not fit the usual IIH demographics and has no other demonstrable cause of increased intracranial pressure.

Diagnosis of arteriovenous malformations

If bleeding is suspected, an unenhanced CT scan will show the hemorrhage. Although unruptured AVMs are typically apparent on an enhanced CT scan, MRI is more sensitive for visualizing small AVMs. MRI demonstrates the heterogeneous signals representing the various elements of the lesion: blood vessels, brain, flowing and clotted blood, calcium, hemorrhage, or edema. Calcified AVMs are sometimes identifiable on plain radiograph or CT scan. Cerebral angiography is required to show the anatomy clearly and to define the feeding and draining vessels of the AVM.

Figure 14-17 Arteriovenous malformation (AVM). A, This 24-year-old man was referred with a 2- to 3-year history of prominent blood vessels in the right eye. Visual acuity was 20/20 bilaterally, but visual fields (B) demonstrated a left homonymous hemianopia. C, A T2-weighted MRI scan demonstrated a large right basal ganglia AVM (red arrow).D, Angiogram of the right internal carotid artery confirmed the basal ganglia AVM (arrow).

(Courtesy of Steven A. Newman, MD.)