Disorders Nerve•Cranial6 SECTIONMotor Ocular Single

Sixth Cranial Nerve Palsy

Key Facts

•Damage to sixth cranial nerve causing incomitant esodeviation with or without abduction deficit

•Common causes:

•reduced perfusion to the intracranial segment of the nerve in diabetes or arteriosclerosis (ischemic palsy) • head trauma

•Uncommon causes:

•compression by intracranial mass lesions • non-infectious, infectious, or neoplastic meningitis • increased intracranial pressure (false-localizing sixth cranial nerve palsy) • multiple sclerosis • other brain stem disorders

•Most urgent rule-out diagnosis: increased intracranial pressure

•Bilateral simultaneous sixth cranial nerve palsies are never caused by ischemia but by:

•increased intracranial pressure • meningeal inflammation or neoplastic

infiltration • clival or pontine tumors

• Brain MRI indicated if ischemic palsy is not a plausible diagnosis

Clinical Findings

•Incomitant esodeviation with or without abduction deficit • No other manifestations need be present (isolated palsy) • If papilledema is present, may be a false-localizing sign secondary to increased intracranial pressure causing downward displacement of the brain and tugging on the sixth cranial nerve

Ancillary Testing

•MRI indicated unless ischemic palsy is a very likely diagnosis • If MRI is negative, lumbar puncture is indicated to rule out meningitis • If all studies are negative, body imaging may be indicated to rule out occult systemic inflammatory or neoplastic disorder • If all studies negative, presume ischemic or idiopathic inflammatory cause and advise monocular occlusion or spectacle prism • If no recovery within 3 months, repeat brain imaging

Differential Diagnosis

• Myasthenia gravis • Graves disease • Orbital myositis • Orbital tumor

Treatment

• For palsies stable for ≥9 months, consider extraocular muscle surgery

Prognosis

•Ischemic palsies: resolution is complete and occurs within 3 months

•Non-ischemic palsies: recovery is variable and is complete within 9 months unless process is ongoing

•Surgical realignment provides satisfactory zone of single binocular vision when there is some abduction preoperatively

•when there is not, the patient may get single binocular vision in straight ahead and contralateral gaze but generally not in ipsilateral gaze

Fig. 6.4 Right sixth cranial nerve palsy. In primary position, the eyes display esotropia. In right gaze, the right eye does not cross the midline. The left eye moves normally. This is a complete sixth cranial nerve palsy; incomplete forms, which are more common, display less obvious features.

Palsy Nerve Cranial Sixth

Disorders Nerve Cranial• 7 SECTIONMotor Ocular Multiple

Unilateral Ophthalmoplegia

Key Facts

•Uniocular ductional deficits that cannot be attributed to dysfunction of a single ocular motor cranial nerve

•May also have ptosis, anisocoria and/or reduced pupil constriction to light, and reduced sensation or pain in distribution of trigeminal nerve

•Lesion usually lies in orbit or cavernous sinus but may be multicentric

•Common causes:

• neoplasm • aneurysm • infection • inflammation • arteriovenous fistula

Clinical Findings

•Uniocular ductional deficits attributable to dysfunction of more than one ocular motor nerve

•May have:

•ptosis • anisocoria and/or reduced pupil constriction to light • reduced sensation or pain in distribution of trigeminal nerve • elevated intraocular pressure • proptosis • resistance to retropulsion • congested eyelids or conjunctiva

Ancillary Testing

•CT adequate for suspected orbital disease, MRI best for retro-orbital disease

•Infection, non-infectious inflammation, fistula, and neoplastic infiltration may produce subtle signs that go unnoticed even on high-grade MRI

•Lumbar puncture often discloses evidence of neoplastic infiltration but may not be sensitive to indolent inflammation

•Arteriovenous fistulas are visible on magnetic resonance angiography source images but catheter cerebral angiography still gold standard

•For lesions originating in paranasal sinuses, biopsy often diagnostic

•Imaging of chest, abdomen, and pelvis helpful in suspected metastatic or multicentric disease

•Bone marrow biopsy helpful in suspected hematopoietic cancer

Differential Diagnosis

•Graves disease

•Orbital myositis

•Orbital tumor

•Traumatic orbitopathy

•Myasthenia gravis

•Fisher syndrome

Treatment

• Depends on process

Prognosis

• Depends on process