Evaluation Guidelines Table142

The following tests may aid in the diagnosis of problems affecting the eleventh and twelfth cranial nerves.

Neuroimaging. Various neuroimaging studies may be useful. y y Plain films of the skull may provide diagnostic information in platybasia (flattening of the base of the skull so that the angle formed by an imaginary line connecting the anterior margin of the foramen magnum, the tuberculum sella, and the nasion is greater than 143 degrees), Paget's disease (areas of increased and decreased bone density, giving the bones a cotton-wool appearance), and basal skull fracture. Head computed tomography (CT) may be diagnostic in meningioma (homogeneous contrast-enhancing lesions with well-defined borders), acoustic neuroma (a well-defined uniformly enhancing tumor in the cerebellopontine angle, along with widening of the internal auditory canal), and skull fracture. Head magnetic resonance imaging (MRI) is useful in the diagnosis of a multitude of lesions including syringobulbia (a syringobulbar cavity), multiple sclerosis (plaques), tuberculous or carcinomatous meningitis (meningeal enhancement), brain abscess (a thin rim of contrast enhancement that surrounds a central

TABLE 14-2 -- USEFUL STUDIES IN EVALUATING LESIONS OF CRANIAL NERVES XI AND XII

Neuroimaging

Electrophysiology

Fluid and tissue Analysis

Other Tests

Supranuclear lesions, unilateral or bilateral

Head MRI, CT

Evoked potentials

CSF

N/A

Supranuclear lesion in pons

Head MRI Head CT

Evoked potentials

CSF

N/A

Nuclear lesions

Head MRI

EMG/NCV

CSF

CBC, throat washings, stool or blood cultures (abscess, polio)

Serum alkaline phosphatase

Chest radiograph, PPD

Serum angiotensin converting enzyme, chest radiograph

Serum VDRL

Lesion within the cranium or in the region of the foramen magnum

Plain skull film Head MRI Head CT

BAER, audiometry

CSF, lymph node biopsy

N/A

Lesions in the region of the jugular foramen

Head MRI

Plain films of head, head CT

N/A

CSF

N/A

Lesions in the retroparotid or retropharyngeal spaces, and far distal peripheral nerve lesions

Neck MRI

N/A

N/A

N/A

EMG/NVC , electromyogram/nerve conduction velocity; CSF, cerebrospinal fluid; CBC, complete blood count; BAER, brain stem auditory evoked response; PPD, purified protein derivative; N/A, not applicable zone of low attenuation), medial medullary syndrome (infarction in the medial medulla), and metastatic cancer. Doppler studies or an angiogram may be useful with regard to the workup of the medial medullary syndrome resulting from vascular occlusion in the posterior circulation.

Electrophysiology. A number of electrophysiological studies may provide valuable diagnostic clues. Electromyography (EMG) with nerve conduction studies may be useful to diagnose Guillain-Barre syndrome (reduction in conduction velocity, slowing of F wave conduction velocity, nerve conduction block), and motor neuron disease (widespread fibrillations and positive sharp waves). Evoked potentials (visual, brain stem auditory, somatosensory) may be useful in the diagnosis of multiple sclerosis.

Cerebrospinal Fluid. Cerebrospinal fluid (CSF) analysis may aid in the diagnosis of lesions of CN XI and XII. Elevated CSF protein level is a feature of multiple sclerosis, neurosarcoidosis, tuberculous meningitis, and poliomyelitis. A low CSF glucose level may be present in tuberculous meningitis, carcinomatous meningitis, and neurosarcoidosis. CSF leukocytosis may be found in neurosarcoidosis and tuberculous meningitis. Albuminocytological dissociation (elevated CSF protein level in the relative absence of CSF leukocytosis) is a feature of Guillain-Barre syndrome. CSF oligoclonal bands are a feature of multiple sclerosis. Cytological examination of cellular material in the CSF may be diagnostic in carcinomatous meningitis. CSF cultures along with analysis of genetic material by polymerase chain reaction may be diagnostic in infections of the CSF. CSF pressure may be elevated in a number of processes including abscesses, neurosarcoidosis, and tuberculous meningitis.

Fluid and Tissue Analysis. Blood work may also be of diagnostic value (e.g., alkaline phosphatase levels in Paget's disease, angiotensin converting enzyme levels in sarcoidosis, Venereal Disease Research Laboratory test [VDRL] in syphilis, viral cultures in poliomyelitis, genetic testing in neurofibromatosis). Purified protein derivative (PPD) is helpful in diagnosing tuberculosis, as is lymph node biopsy in sarcoidosis.

Neuropsychological Tests. This technique has limited value in diagnosis of processes involving CN XI and XII.

Other Tests. Plain films of the chest are of diagnostic value in evaluating pulmonary disorders that extend beyond the pleura to involve CN XI, including tuberculosis, lung carcinoma, and pulmonary sarcoidosis.

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