Cerebral aneurysms are localized dilations of the vessel wall. They are present in approximately 5% of the population but rarely become symptomatic before 20 years of age. Cerebral aneurysms may be an isolated finding and are commonly associated with hypertension. Less common predisposing conditions include arteriovenous malformations (AVMs), coarctation of aorta, polycystic kidney disease, and connective tissue diseases (eg, fibromuscular dysplasia, Marfan syndrome, and Ehlers-Danlos syndrome). A familial occurrence is possible, and tobacco use is a risk factor. Among patients with cerebral aneurysm, 10% will have more than 1.
Figure 14-14 shows possible locations for cerebral aneurysms. The most common type of intracranial aneurysm is the saccular, or “berry,” aneurysm that arises at arterial bifurcations. Of these aneurysms, 90% are supratentorial and 10% are infratentorial. Aneurysms arising from the internal carotid artery and basilar artery may produce neuro-ophthalmic manifestations. In general, aneurysms larger than 10 mm are most likely to rupture. If they are 25 mm or larger, they are termed “giant aneurysms.” Because high morbidity and mortality result from aneurysm rupture, early detection and surgical intervention can be life-saving.
Figure 14-14 Drawing shows locations for intracranial aneurysms arising from cerebral blood vessels. ACoA = anterior communicating artery, BA = basilar artery, ICA = internal carotid artery, MCA = middle cerebral artery, PCA = posterior cerebral artery, PCoA = posterior communicating artery, SCA = superior cerebellar artery, VA = vertebral artery.
(Reprinted from Kline LB, Foroozan R, eds. Optic Nerve Disorders. 2nd ed. Ophthalmology Monographs 10. New York: Oxford University Press, in cooperation with the American Academy of Ophthalmology; 2007:131.)
Clinical presentation of cerebral aneurysms
Unruptured aneurysms, particularly giant aneurysms, may cause progressive neurologic dysfunction because of their mass effect. An ophthalmic artery aneurysm may cause a progressive unilateral optic neuropathy and ipsilateral periocular pain. Anterior communicating artery aneurysms may cause loss of vision by compressing the optic chiasm or optic tract. Aneurysms at the junction of the internal carotid and posterior communicating arteries cause an ipsilateral CN III palsy. Any complete CN III palsy with pupil involvement and any partial CN III palsy with or without pupil involvement should raise suspicion for an aneurysm and prompt immediate neuroimaging. Diagnostically, pain is not a helpful symptom, because it may occur with CN palsies from microvascular ischemia and may be absent with unruptured aneurysms. TIAs, cerebral infarction, and seizures may be caused by flow phenomena or distal embolization.
Intracavernous carotid artery aneurysms typically produce a cavernous sinus syndrome. These aneurysms are often a fusiform enlargement (dolichoectasia) and not saccular. CNs III, IV, and VI and the ophthalmic branch of CN V are involved, singly or in combination. Because they are confined by the walls of the cavernous sinus, these aneurysms typically do not rupture, instead causing progressive neurologic dysfunction. Aneurysms in this location often produce facial pain and should be considered in the differential diagnosis of painful ophthalmoplegia.
A ruptured aneurysm is a neurosurgical emergency. Patients exhibit symptoms and signs of subarachnoid or intraparenchymal hemorrhage. The headache resulting from a ruptured aneurysm may be localized or generalized and is often described as “the worst of my life.” Nausea, vomiting, and neck stiffness signify meningeal irritation from subarachnoid blood. In rare cases, fever may be present. Elevated intracranial pressure may produce papilledema and CN VI palsies. Patients may be disoriented, lethargic, or comatose. Altered mental status is a poor prognostic sign.
Ocular hemorrhage may accompany subarachnoid hemorrhage. Intraretinal, preretinal, subhyaloid, vitreous, subconjunctival, orbital, or optic nerve sheath hemorrhage may be present. Ocular hemorrhages are most likely produced when intracranial pressure in the optic nerve sheath exceeds ocular venous pressure, reducing ophthalmic venous drainage and causing venous rupture. The combination of vitreous and subarachnoid hemorrhage is called Terson syndrome (Fig 14-15). Many patients recall symptoms of a “sentinel bleed” before the major rupture. Transient or mild neurologic symptoms with headache are most commonly described.
Diagnosis of cerebral aneurysms
Any patient suspected of harboring an aneurysm requires urgent neuroradiologic investigation. The specific type of study ordered varies, and the decision should involve the neuroradiologist (see Chapter 2).
CTA is the imaging modality of choice for diagnosis of clinically relevant aneurysms at most sites. MRI demonstrates most aneurysms larger than 5 mm, and high-quality MRA can detect aneurysms as small as 3 mm. CTA or MRA is useful to screen for unruptured aneurysms; both procedures are less expensive and associated with lower morbidity than conventional angiography (Fig 14-16). However, if there is a high level of suspicion for aneurysm, a negative finding on MRA or CTA does not obviate the need for the “gold standard” evaluation using conventional cerebral arteriography.
CT is useful immediately after aneurysm rupture to detect the presence of intraparenchymal and subarachnoid blood. An enhanced CT scan can demonstrate large aneurysms, but CT alone is not an acceptable screening test for unruptured aneurysms. If subarachnoid hemorrhage is suspected and the CT finding is negative, CTA or lumbar puncture is needed to confirm the presence of subarachnoid blood. However, a lumbar puncture should not be attempted in the presence of midline shift or evidence of cerebral (uncal) herniation.
Figure 14-15 Fundus photograph shows consequences of a ruptured intracranial aneurysm, which may produce hemorrhage within the retina, preretinal space, or vitreous (Terson syndrome).
(Courtesy of Steven A. Newman, MD.)
Figure 14-16 Imaging of cerebral aneurysms. A, Sagittal view of the brain on a T2-weighted MRI scan shows a low-intensity signal in the subarachnoid space anterior to the medulla (arrow), contiguous with the vertebral artery inferiorly, consistent with flowing blood. B, Conventional arteriography shows a vertebral artery aneurysm (arrow).C, The same aneurysm, as demonstrated by magnetic resonance angiography (MRA) (arrow).
(Courtesy of Leo Hochhauser, MD.)
Prognosis for patients with cerebral aneurysms
Modern imaging technology (MRA and CTA) has dramatically increased the detection of unruptured intracranial aneurysms. The risk of rupture is related to the size of the aneurysm. Aneurysms that are 7–12 mm, 13–24 mm, and 25 mm or greater have a yearly rupture rate of 1.2%, 3.1%, and 8.6%, respectively. Once an aneurysm has ruptured, morbidity and mortality are high. The proportion of patients who die at the time of rupture is 30%. If untreated, another 33% die within 6 months of rupture, and 15% more die within 10 years. Many of those who survive suffer severe neurologic deficits.
Wiebers DO, Whisnant JP, Huston J III, et al. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet. 2003; 362(9378):103–110.
Treatment of cerebral aneurysms
Treatment of symptomatic aneurysms before rupture is ideal and should be performed without delay. Supportive treatment to stabilize the patient includes efforts to lower intracranial pressure (via hyperventilation or administration of mannitol), treat cerebral vasospasm (with calcium channel blockers and blood volume expansion), control blood pressure, and prevent seizures.
The definitive treatment is surgical clipping of the aneurysm; however, endovascular techniques such as coil embolization or stent placement are replacing clipping as the preferred treatment for many aneurysms, depending on the aneurysm’s size, location, and anatomy.
Thompson BG, Brown RD Jr, Amin-Hanjani S, et al. Guidelines for the management of patients with unruptured intracranial aneurysms: a guideline for the healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2015; 46(8):2368–2400.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.