Evaluation Guidelines Table95

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Neuroimaging. Lesions of cranial nerves III, IV, and VI may occur anywhere along the course of the nerves, from the nuclei in the brain stem to the orbits. The possibility of focal neoplastic or inflammatory lesions requires evaluation with neuroimaging. Magnetic resonance imaging is more reliable than computed tomography for detecting brain stem, subarachnoid space, or cavernous sinus lesions. Magnetic resonance imaging is also the best procedure for imaging the orbits when fat suppression (saturation) pulse sequences and gadolinium enhancement are used. Fat suppression renders the orbital fat dark so that any gadolinium enhancement (white) within the fat, muscles, or optic nerve can be reliably observed. Thin-section computed tomography is still a potent imaging technique for supratentorial brain lesions and orbital study. It also is a cost-effective means to measure the extraocular muscle diameter and is a sensitive indicator of thyroid orbitopathy.

Saccular aneurysms remain a frequent and important cause of cranial nerve III palsy, and cerebral angiography should be used in evaluating third nerve dysfunction because it is the only reliable way of finding such lesions. Because false-negative and false-positive results continue to be problematic, magnetic resonance angiography (MRA) cannot yet be used in place of standard angiography. False-positive MRA studies can lead the physician to interpret vascular loops as aneurysms, resulting in unnecessary surgical intervention. In the future, with improvements in MRA imaging quality, this procedure may become a reliable

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TABLE 9-5 -- USEFUL STUDIES IN THE EVALUATION OF SYNDROMES INVOLVING CRANIAL NERVES III,

V, AND VI

Syndrome

Neuroimaging

Electrophysiology

Fluid and Tissue Analysis

Neuropsychology Tests

OtherTests

Anisoccoria

MRI/CT brain and cervical spine; MRI: orbits with fat suppression and gadolinium

N/A

CSF analysis

N/A

Testing with pilocarpine, cocaine, hydroxyamphetamine; chest x-ray study

Adie's pupil

MRI: brain; orbits with fat suppression and gadolinium; CT: orbits

N,/A

N/A

N/A

Testing with pilocarpine, cocaine, hydroxyamphetamine; chest x-ray study

Light-near dissociation

MRI brain: midbrain

EMG/NCV: peripheral neuropathy, Miller-Fisher variant of Guillain-Barre syndrome

CSF analysis, RPR, VDRL, fasting glucose

N/A

Testing with pilocarpine, cocaine, hydroxyamphetamine; chest x-ray study

Bilateral unreactive pupils

MRI brain: midbrain

CSF analysis

N/A

Testing with pilocarpine, cocaine, hydroxyamphetamine; chest x-ray study

Impaired smooth pursuit

MRI brain: parieto-occipital lobe, brain stem

N/A

HIV, drug screen, genetic studies (HD)

N/A

N/A

Impaired saccadic movements

MRI brain: frontal lobe, brain stem

N/A

TFTs, genetic studies (HD), HIV, immunoglobulins (AT) enzyme studies: Tay-Sachs' and Gauchers diseases

N/A

Jejunal biopsy: Whipple's disease; bone marrow biopsy: Niemann-Piek

Gaze palsies

MRI brain: brain stem

N/A

CSF analysis

N/A

N/A

Skew deviation

MRI brain: brain stem

N/A

N/A

N/A

N/A

Ocular misalignment

MRI brain: brain stem, orbits

EMG/NCV: MG, botulism

CSF, muscle biopsy, fasting glucose

N/A

N/A

Nystagmus, central

MRI brain: brain stem

N/A

CSF analysis, drug screen, electrolytes

N/A

N/A

Ocular flutter/Opsoclonus

MRI brain: brain stem

N/A

CSF analysis, drug sereen, antineuronal antibodies

N/A

Chest/abdominal/pelvic CT

Monocular diplopia

MRI brain: occipital lobe (binocular)

N/A

N/A

N/A

Ophthalmological examination

Binocular diplopia

MRI brain: brain stem, orbits

EMG/NCV: MG, botulism

CSF analysis, drug screen, fasting glucose, muscle biopsy

N/A

N/A

Cavernous sinus syndrome

MRI brain (cavernous sinus, parasellar); MRA; cerebral angiography; orbital venography

N/A

CSF analysis

N/A

N/A

Orbital syndromes

MRI: orbits with fat suppression and gadolinium; CT: orbits

N/A

CSF analysis

N/A

N/A

AT, Ataxia-telangiectasia; CSF, cerebrospinal fluid; CT, computed tomography; EMG, electromyography; HD, Huntington's disease; HIV, human immunodeficiency virus; MG, myasthenia gravis; MRA, magnetic resonance angiography; MRI, magnetic resonance imaging; N/A, not applicable; NCV, nerve conduction velocity; TFTs, thyroid function tests.

AT, Ataxia-telangiectasia; CSF, cerebrospinal fluid; CT, computed tomography; EMG, electromyography; HD, Huntington's disease; HIV, human immunodeficiency virus; MG, myasthenia gravis; MRA, magnetic resonance angiography; MRI, magnetic resonance imaging; N/A, not applicable; NCV, nerve conduction velocity; TFTs, thyroid function tests.

technique for excluding an aneurysm in the setting of third nerve dysfunction.

Electrophysiology. Brain stem auditory evoked responses, somatosensory evoked responses, and pattern-reversal visually evoked responses are commonly used as indicators of demyelinating lesions, which can affect the conjugate gaze mechanisms and the individual cranial nerves as they course through the brain stem. There is no widely available electrophysiological method to examine the peripheral portions of the cranial nerves III, IV, and VI.

Fluid and Tissue Analysis. Thyroid function testing is important to identify patients with thyroid orbitopathy, but it must be remembered that nearly a half of patients have normal thyroid function at the time they present with orbital manifestations. Patients with lead and other heavy metal poisoning can present with elevated intracranial pressure and false-localizing cranial nerve VI palsy. Urine screen for heavy metals is an important adjunct to the workup of these patients.

Cerebrospinal Fluid. Cerebrospinal fluid (CSF) examination is often a critical part of investigation for dysfunction of cranial nerves III, IV, and VI because these nerves are often affected selectively in meningeal infections, as well as in inflammatory and neoplastic infiltrating disorders. In addition, patients with multiple sclerosis (see Chapter...48 ) may present a typical profile of CSF abnormalities, and patients with this disease often present with ocular motility disturbance from central lesions (gaze palsy, INO) and less frequently with ophthalmoplegia from plaques affecting the intramedullary portion of cranial nerves III, IV, or VI.

Neuropsychological Testing. There are no common specific indications for neuropsychological testing in patients with ocular motility disturbances, although altered pursuit or saccade dynamics may result from cerebral pathology that also affects higher cortical mental functions.

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