neurologic disorders
Third Cranial (Oculomotor) Nerve Disorders
Diagnosis of Third Cranial Nerve Disorders
Clinical evaluation CT or MRI Differential diagnosis for third cranial nerve disorders includes Midbrain lesions that disrupt the oculomotor fascicle (Claude syndrome, Benedict syndrome) Leptomeningeal tumor or infection Cavernous sinus disease (giant carotid aneurysm, fistula, or thrombosis) Intraorbital structural lesions (eg, orbital mucormycosis) that restrict ocular motility Ocular myopathies (eg, due to hyperthyroidism or mitochondrial disorders) Disorders of the neuromuscular junction (eg, due to myasthenia gravis or botulism) Differentiation may be clinical. Exophthalmos or enophthalmos, a history of severe orbital trauma, or an obviously inflamed orbit suggests an intraorbital structural disorder. Graves orbitopathy (ophthalmopathy) should be considered in patients with bilateral ocular paresis, paresis of upward gaze or abduction, exophthalmos, lid retraction, lid lag during downward gaze (Graefe sign), and a normal pupil. CT or MRI is required. If a patient has a dilated pupil and a sudden, severe headache (suggesting ruptured aneurysm) or is increasingly unresponsive (suggesting herniation), neuroimaging (CT or, if available, MRI) is done immediately. If a ruptured aneurysm is suspected and CT (or MRI) does not show blood or is not available rapidly, other tests, such as lumbar puncture, magnetic resonance angiography, CT angiography, or cerebral angiography, are indicated. Cavernous sinus disease and orbital mucormycosis require immediate MRI imaging for timely treatment. 