Arteriovenous Malformations

KEY FEATURES

Essentials of Diagnosis

• Sudden onset of subarachnoid or intracerebral hemorrhage

• Distinctive neurologic signs reflect the region of the brain involved

• Signs of meningeal irritation in patients presenting with subarachnoid hemorrhage

• Seizures or focal deficits may occur

General Considerations

• Result from a localized maldevelopment of part of the primitive vascular plexus

• Consist of abnormal arteriovenous communications without intervening capillaries

• Vary in size, ranging from massive lesions that are fed by multiple vessels and involve a large part of the brain to lesions so small that they are hard to identify at arteriography, surgery, or autopsy

• In approximately 10% of cases, there is an associated arterial aneurysm, while 1–2% of patients presenting with aneurysms have associated arteriovenous malformations (AVMs)

• Clinical presentation may relate

  • To hemorrhage from the malformation or an associated aneurysm

  • To cerebral ischemia due to diversion of blood by the anomalous arteriovenous shunt or due to venous stagnation

• Regional maldevelopment of the brain, compression or distortion of adjacent cerebral tissue by enlarged anomalous vessels, and progressive gliosis due to mechanical and ischemic factors may also be contributory

Demographics

• Up to 70% of AVMs bleed, most commonly before the age of 40

CLINICAL FINDINGS

Symptoms and Signs

• Initial symptoms consist of

  • Hemorrhage in 30–60% of cases

    • Commonly intracerebral as well as into the subarachnoid space

    • Fatal in about 10% of cases

  • Recurrent seizures in 20–40%: more likely with frontal or parietal AVMs

  • Headaches in 5–25%

    • Especially likely when the external carotid arteries are involved in the malformation

    • Sometimes simulate migraine but more commonly are nonspecific in character, with nothing about them to suggest an underlying structural lesion

  • Miscellaneous reports (including focal deficits) in 10–15%

• Brainstem and cerebellar AVMs may cause obstructive hydrocephalus

• Abnormal mental status and signs of meningeal irritation in patients with subarachnoid hemorrhage

• Additional findings may help localize the lesion and sometimes indicate that intracranial pressure is increased

• Cranial bruit

  • Always suggests the possibility of a cerebral AVM

  • May also be found with aneurysms, meningiomas, acquired arteriovenous fistulas, and arteriovenous malformations involving the scalp, calvarium, or orbit

  • Best heard over the ipsilateral eye or mastoid region

  • May be helpful in lateralization but not in localization

  • Absence of a bruit does not exclude the possibility of AVM

Differential Diagnosis

• Aneurysmal hemorrhage

• Intracerebral hemorrhage from other causes

• Space-occupying lesion, eg, brain tumor

DIAGNOSIS

Imaging Studies

• CT scanning

  • Indicates whether subarachnoid or intracerebral bleeding has recently occurred

  • Helps localize source of bleeding

  • May reveal the AVM

• Arteriography

  • If the source of hemorrhage is not evident on the CT scan, arteriography is necessary to exclude aneurysm or ...