Third Nerve Palsy (Oculomotor Nerve Palsy) Workup

Updated: Oct 08, 2018
  • Author: James Goodwin, MD; Chief Editor: Andrew G Lee, MD  more...
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Workup

Approach Considerations

Angiographic imaging studies (eg, computed tomographic angiography [CTA], magnetic resonance angiography [MRA], digital subtraction angiography [DSA]) are often necessary in the evaluation of acute oculomotor nerve palsy.

The combination of CT scanning/CTA followed by MRI/MRA is often necessary in the evaluation of unexplained oculomotor nerve palsy. Standard catheter angiography may be required upon high clinical suspicion for aneurysm.

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Imaging Studies

In the acute setting, CTA is more sensitive than MRA in detecting aneurysms that cause oculomotor palsy. Both modalities can be used to detect aneurysms that are 4 mm in diameter or larger. DSA is the criterion standard and can reveal aneurysms smaller than 3 mm. If aneurysm is not the only pathology in the differential diagnoses, MRI and CTA combined is the most powerful imaging option. [24] Noncontrast CT scan of the head can cause subarachnoid hemorrhage in patients with third nerve palsy due to an underlying ruptured aneurysm.

MRI/MRA

MRI is a more sensitive imaging technique than CT scan for the evaluation of a nonaneurysmal cause of third nerve palsy (inflammation, demyelination, ischemic infarction, abscess, or tumor).

MRI is also the procedure of choice for demonstrating meningeal and dural inflammation and infiltration.

Abnormal signal intensity and enhancement in the intracavernous portion of the third cranial nerve has been demonstrated in a case of herpes zoster with third cranial nerve palsy. [25]

Special MR sequences such as diffusion-weighted imaging (DWI) can demonstrate a small and acute infarct in the midbrain involving the intraparenchymal segment of the third cranial nerve in a patient with acute onset third cranial nerve palsy. [26]

MRI/MRA also gives more specific information than CT scan on vascular flow patterns and is better for picking up lesions in the cavernous sinus, including aneurysm.

MRA using 1.5-Tesla or lower strength magnet is probably not adequate to rule out berry aneurysm causing third cranial nerve palsy, although 3-Tesla MRA with special attention to the circle of Willis can be definitive in this regard because of enhanced resolution.

CT scanning

CT scan is more sensitive than MRI to demonstrate subarachnoid hemorrhage.

CT scan is also better than MRI for demonstrating calcification within lesions, as may be found in certain tumors and in large aneurysms.

Sixteen-row multislice CT angiography rivals digital subtraction catheter angiography in sensitivity and specificity for detecting intracranial aneurysms. [27, 28]

CTA is faster than MRI/MRA and, in many centers, is superior to MRI/MRA for aneurysm.

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Procedures

Lumbar puncture

The main purpose of lumbar puncture is to demonstrate the presence of blood in cerebrospinal fluid, an inflammatory reaction, neoplastic infiltration, or infection.

Bloody spinal fluid with oculomotor nerve palsy usually results from rupture of a posterior communicating artery berry aneurysm.

Meningeal inflammatory reaction may be idiopathic or may result from a specific infection that should be diagnosed by bacterial and fungal cultures and by fungus, protozoan, or virus-specific serology or specific antigen (polymerase chain reaction).

Cerebral angiography

Conventional angiography is the definitive test for berry aneurysm in all intracranial locations.

A small but definite risk of angiography causing serious complication, such as embolic stroke, exists. This risk varies with each institution and individual who does the procedure.

Angiography is indicated in a patient with third cranial nerve palsy and dilated, light-fixed pupil. It may be indicated in a patient younger than 55-60 years, especially without a history of long-standing diabetes, hypertension, or both.

When external ophthalmoplegia is partial, pupil sparing is not a reliable indicator of ischemia as opposed to aneurysm as the etiology, so angiography may be warranted in this setting, especially if the patient is young or lacks ischemic risk factors. See the image below.

Angiography anteroposterior and lateral views, lef Angiography anteroposterior and lateral views, left posterior communicating artery aneurysm, indicated by red arrow. Courtesy of James Goodwin, MD.
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Histologic Findings

Cytologic examination of cerebrospinal fluid is used to diagnose meningeal carcinomatosis and lymphomatous or leukemic infiltration.

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Laboratory Studies

Blood glucose and hemoglobin A1c measurements can help determine if the patient is diabetic and, if so, how well-controlled the diabetes is. The presence of vasculopathic risk factors supports, but does not confirm, microvascular ischemia as a cause of oculomotor palsy. Although microvascular ischemia is the most common cause of isolated cranial nerve palsy in patients with vasculopathic risk factors (eg, diabetes, hypertension, hypercholesterolemia, smoking), a considerable number of patients have other causes. In addition, many patients with other causes of oculomotor palsy have vasculopathic risk factors. [29] Evaluation for giant cell arteritis (eg, erythrocyte sedimentation rate, C-reactive protein, temporal artery biopsy) may be helpful in elderly patients.

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