Figure 14-12 Axial FLAIR MRI scan showing reversible bilateral posterior circulation signal abnormalities in a patient with transient cortical blindness and preeclampsia. (Courtesy of Lanning B. Kline, MD.)

Finocchi V, Bozzao A, Bonamini M, et al. Magnetic resonance imaging in posterior reversible encephalopathy syndrome: report of three cases and review of literature. Arch Gynecol Obstet. 2005;271(1):79–85. Epub 2004 Oct 9.

Lymphocytic Hypophysitis

Lymphocytic hypophysitis is a rare neuroendocrine disorder characterized by autoimmune inflammation of the pituitary gland, with various degrees of pituitary dysfunction, including permanent hypopituitarism. Histologic findings consist of an initial monoclonal lymphocytic infiltrate, which can heal with minimal sequelae or progress to fibrosis. Clinical presentation may mimic a pituitary tumor, including chiasmal visual field defects and acute-onset diabetes insipidus. Imaging characteristics and endocrine testing are not specific. The diagnosis should be considered if these symptoms and signs occur during pregnancy, but surgical treatment is typically required if vision is compromised.

Cerebrovascular Disorders

Comprehensive discussion of cerebrovascular disorders is beyond the scope of this text. An overview of common conditions causing neuro-ophthalmic signs and symptoms is given in the following sections.

Transient Visual Loss

Transient neurologic or ophthalmic symptoms in middle-aged or elderly patients suggest a vascular origin. Localization of the symptoms and signs determines whether they result from ischemia in the vertebrobasilar or the carotid artery territory. Although recurrent cerebrovascular ischemia is a concern, the major cause of death in these patients is coronary artery disease. Thus, efforts should be made to control risk factors for cardiovascular disease, such as hypertension, diabetes mellitus, and hyperlipidemias, accompanied by cessation of smoking. Diagnostic and therapeutic efforts are directed at the cerebrovascular circulation. Carotid system disorders whose main symptom is transient visual loss are discussed in Chapter 5.

Vertebrobasilar System Disease

The vertebrobasilar arterial system (posterior circulation) is composed of the vertebral, basilar, and posterior cerebral arteries. These blood vessels supply the occipital cortex, brainstem, and cerebellum.

Clinical presentation of vertebrobasilar insufficiency

Patients with vertebrobasilar insufficiency often present to the ophthalmologist first, because ocular motor and visual symptoms are prominent (Fig 14-13). Nonophthalmic symptoms of transient

closely mimicking the scintillating scotomata of migraine. These attacks are frequently repetitive and may occur alone or in combination with the other transient symptoms of vertebrobasilar insufficiency just mentioned. Migraine can produce similar symptoms, with or without an associated headache, and is discussed in Chapter 12.

Homonymous visual field changes without other neurologic symptoms suggest involvement of the posterior circulation. Highly congruous homonymous visual field defects without other systemic symptoms are typical of occipital lobe infarcts. Patients reporting reading difficulties without an obvious cause should undergo a careful visual field and Amsler grid examination in search of centrally located congruous homonymous visual field defects.

The visual manifestations of cortical infarction are detailed in Chapter 4. Cerebral and cortical blindness, caused by bilateral occipital lobe lesions, is characterized by amaurosis, normally reactive pupils, and an unremarkable fundus appearance. Frequently, patients with cerebral blindness will deny their blindness (Anton syndrome) (see Chapter 6).

Ocular motor disturbances are common with vertebrobasilar insufficiency, and diplopia is a frequent complaint. Examination may reveal horizontal or vertical gaze palsies, internuclear ophthalmoplegia, skew deviation, ocular motor cranial nerve palsies, or nystagmus. An ipsilateral, central Horner syndrome may be present with pontine or medullary infarcts (Wallenberg syndrome).

Levin LA. Topical diagnosis of chiasmal and retrochiasmal disorders. In: Miller NR, Newman NJ, Biousse V, Kerrison JB, eds. Walsh and Hoyt’s Clinical Neuro-Ophthalmology. Vol 1. 6th ed. Philadelphia: Lippincott Williams & Wilkins; 2005:539–554.

Etiologies of posterior circulation ischemia

The most frequent causes of vertebrobasilar TIAs and stroke are atheromatous occlusion, hypertensive vascular disease (lacunar infarction), microembolization (either from the vertebrobasilar system or from the heart), fluctuations in cardiac output, and arterial dissection. The following conditions have all been associated with symptoms and signs of vertebrobasilar ischemia: polycythemia, hypercoagulable states, congenital aplasia or hypoplasia of a vertebral or posterior communicating artery, anemia, and vasospasm. Mechanical factors such as cervical spondylosis and chiropractic manipulation of the cervical spine have also been implicated in vertebrobasilar occlusions resulting in severe neurologic deficits. A less common cause of vertebrobasilar dysfunction is a reversal of blood flow in the vertebral artery (subclavian steal); this reversal is caused by a proximal occlusion of the subclavian artery that produces an unusual alteration in the direction of flow in the ipsilateral vertebral artery. Lowered pressure in the distal segment of the subclavian artery can siphon, or “steal,” blood from the vertebral artery and produce fluctuating symptoms of vertebrobasilar artery insufficiency.

Clinical and laboratory evaluation of posterior circulation ischemia

The evaluation for posterior circulation ischemia is similar to the medical workup for carotid system disease. Neuroimaging should be performed on all patients with homonymous visual field defects and other signs of brainstem or cerebellar dysfunction. Magnetic resonance angiography (MRA) and computed tomographic arteriography (CTA) are the best noninvasive methods of evaluating the posterior circulation. Carotid Doppler imaging is not sufficient for evaluating suspected posterior circulation symptoms. Sometimes conventional angiography is necessary to visualize the aortic arch, the configuration of the vertebrobasilar vessels, and the extent of filling from the anterior circulation through the circle of Willis.

The clinician is much less likely to find a treatable structural vascular abnormality with posterior circulation ischemia than with carotid system disease. The evaluation of these patients generally emphasizes a search for underlying cardiac or systemic disorders, including hypercholesterolemia, hypertension, diabetes mellitus, and postural hypotension. Cardiac evaluation should potentially include echocardiography.

Khan S, Cloud GC, Karry S, Markus HS. Imaging of vertebral artery stenosis: a systematic review. J Neurol Neurosurg Psychiatry. 2007;78(11):1218–1225. Epub 2007 Feb 7.

Treatment of vertebrobasilar ischemia

Most patients with vertebrobasilar TIAs are treated medically with antiplatelet therapy or anticoagulants. Intravascular stent placement can be used in select patients with either carotid artery or vertebrobasilar stenosis.

Cerebral Aneurysms

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. They may be an isolated finding and are commonly associated with hypertension. Less common predisposing conditions include arteriovenous malformations, coarctation of the aorta, polycystic kidney disease, and connective tissue diseases (such as fibromuscular dysplasia, Marfan syndrome, and Ehlers-Danlos syndrome). A familial occurrence is possible, and tobacco use is a risk factor.

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. Aneurysms are termed “giant aneurysms” if they are 25 mm or larger. 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, VA = vertebral artery. (Reprinted from Kline LB, Foroozan R, eds. Optic

Nerve Disorders. 2nd ed. Ophthalmology Monograph 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 third nerve palsy. Any complete third nerve palsy with pupil involvement and any partial third nerve palsy with or without pupil

involvement should raise suspicion of an aneurysm and prompt immediate neuroimaging. Pain is not a helpful symptom diagnostically, as it may occur with cranial nerve 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 often are a fusiform enlargement (dolichoectasia) and not berry type. Cranial nerves (CN) 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 but cause 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 of a ruptured aneurysm is often described as “the worst of my life” and may be localized or generalized. 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 sixth nerve 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.

Figure 14-15 Fundus photograph showing 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.)

Diagnosis of cerebral aneurysms

Any patient with a suspected aneurysm requires urgent neuroradiologic investigation. The specific type of study ordered varies, and the decision should involve the neuroradiologist (see Chapter 2). A 4-vessel study of both carotid and vertebral arteries is imperative, because 10% of patients have multiple aneurysms.

CT angiography 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. CT angiography 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 CT angiography does not obviate the need for the “gold standard” evaluation using conventional cerebral arteriography.

Figure 14-16 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 MRA

(arrow). (Courtesy of Leo Hochhauser, MD.)

Computed tomography scanning 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 scanning alone is not an acceptable screening test for unruptured aneurysms. If subarachnoid hemorrhage is suspected and the CT finding is negative, CT angiography or lumbar puncture is indicated 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.

Prognosis for patients with cerebral aneurysms

Modern imaging technology (MRA, CT angiography) has dramatically increased the detection of unruptured intracranial aneurysms. Risk of rupture is related to size; aneurysms <10 mm have a rupture rate of <0.05% per year, and giant aneurysms (≥25 mm) have a 6% rupture rate in the first year. 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.