ABSTRACT
Paranasal sinus mucoceles are an uncommon cause of isolated palsies of cranial nerves III, IV, and VI. The trochlear nerve has been reported to be less frequently affected than the abducens and oculomotor nerves. Isolated sphenoid sinus diseases may cause serious complications by involving adjacent vital structures such as the optic nerve, cavernous sinus, internal carotid artery, and cranial nerves III–VI. We report a case of a 76-year-old woman who presented to our emergency department with a chief complaint of acute double vision and headache. Her diplopia was diagnosed as left trochlear nerve palsy. Brain CT and MRI revealed expanding cystic lesions in both sphenoid sinuses with bony erosion of the left sinus wall. The patient underwent an endoscopic intranasal sphenoidotomy and recovered completely from diplopia at postoperative 2 months. The relationship between the trochlear nerve palsy and its anatomy is also discussed.