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Increasingly frequent headaches and blurred vision had affected a 74-year-old woman for several months. Double vision, which initially occurred only when the patient looked to the right, had started to affect vision when she looked straight ahead. Her eye movements when looking to the left were normal; the right eye, however, did not go beyond midline when looking to the right. Upward and downward gaze were not affected.
Increasingly frequent headaches and blurred vision had affected a 74-year-old woman for several months. Double vision, which initially occurred only when the patient looked to the right, had started to affect vision when she looked straight ahead. Her eye movements when looking to the left were normal (A); the right eye, however, did not go beyond midline when looking to the right (B). Upward and downward gaze were not affected. Sixth nerve palsy was diagnosed.
Dr Joel M. Schwartz of Irvington, NY, writes that the sixth cranial nerve, or abducens nerve, has a long intracranial course ending in innervation of the lateral rectus muscle. The action of this muscle is to rotate the globe laterally; hence the lack of ipsilateral lateral gaze in this patient with right sixth nerve palsy.
Most sixth nerve palsies occur in the elderly or in persons with diabetes because of ischemia. Typically the condition resolves spontaneously within 2 months and requires no further evaluation. Additional workup is warranted if the palsy fails to resolve or if the patient is younger than 50 years or has persistent pain or other cranial nerve palsies. Under these circumstances, obtain CT or MRI images of the brain, orbit, and cavernous sinus to evaluate for tumoral involvement of the cavernous sinus (including tumors that extend from the nasopharynx or are primary in the cavernous sinus, clivus, or meninges), intracranial mass lesions, basilar skull fracture, aneurysm, or multiple sclerosis.
In this case, a conventional spin echo MRI revealed a large aneurysm in the right cavernous sinus. Thrombus filled most of the aneurysm. Magnetic resonance angiography (MRA) was performed to determine whether any of the lumen was patent. A frontal view time-of-flight MRA showed a large right internal carotid artery aneurysm (C). On this sequence, it is impossible to distinguish between the intra-aneurysmal clot and the flowing blood, since both appear bright. Phase contrast MRA-a subtraction technique that suppresses bright objects such as thrombi-is seen in Figure D. On this scan, an arrow identifies the flow in the patent portion of the aneurysm.
The patient underwent surgical closure of the right common carotid artery because the aneurysm could not be closed with intravascular techniques. Her headaches have ameliorated; however, the sixth nerve palsy persists.