In idiopathic cases, no other cranial nerves are involved, and improvement should occur within 2 mo. One identifiable cause is compression of the 6th nerve in the cavernous sinus by a tumor originating in the nasopharynx. Typically, severe pain in the head and anesthesia in the distribution of the first division of the 5th nerve also occur. Anything that causes the brain to shift may stretch the 6th nerve because of the acute angle it makes before entering Dorello's canal. Thus 6th nerve palsies may be due to large brain tumors remote from the nerve, to increased intracranial pressure, or to lumbar puncture.
Diabetic infarction is one of the more common causes.
Wernicke's encephalopathy, aneurysm, and multiple sclerosis. In children without evidence of increased intracranial pressure, these palsies can result from respiratory infection and thus may be recurrent. Diagnosing complete 6th cranial nerve palsies is easy, but determining their etiology can be more challenging. MRI or CT can help exclude intracranial mass lesions, hydrocephalus, and direct nerve compression by lesions in the orbit, cavernous sinus, and base of the skull. Lumbar puncture determines the CSF opening pressure and can detect leptomeningeal inflammatory, infectious, or neoplastic infiltrates entrapping the 6th nerve.