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.