Trochlear nerve palsy with subarachnoid hemorrhage in ambient cistern

Introduction: Subarachnoid hemorrhage in the perimesencephalic cistern is usually of unknown etiology. It is diagnosed by headache or signs of meningeal irritation, which are rarely accompanied by impaired consciousness or central nervous system disturbances, including cranial nerve palsies. The author reports a case of subarachnoid hemorrhage in the perimesencephalic cistern showing ipsilateral trochlear nerve palsy with sudden onset of headache. Case Report: A 66-year-old man presented headache with diplopia. Neurological examination, including Bielschowsky head-tilt test revealed left isolated trochlear nerve palsy, without any other central nerve system disorders. Magnetic resonance image revealed subarachnoid hemorrhage at the left ambient cistern. The mass of dense hematoma clot in the ambient cistern brought to ipsilateral trochlear nerve palsy. Neural dysfunction improved with following hematoma disappearance. Conclusion: It is a rare case of isolated trochlear nerve palsy associated with perimesencephalic subarachnoid hemorrhage.