Arachnoid Cyst in Oculomotor Cistern
A 29-year-old woman with progressive blurred vision and diplopia for 7 years was admitted for further evaluation. Ophthalmological examination revealed right oculomotor nerve palsy as ptosis and downward deviations in the right eye. In room light, pupils measured 6 mm in the right eye and 3 mm in the left eye.\nOrbit MRI was performed using 3.0T system (Magnetom Verio; Siemens Medical Solutions, Erlangen, Germany). T2-weighted axial MR images with heavily T2-weighted 3D turbo spin-echo sequence revealed a hyperintense lesion with an internal hypointense linear structure in the right orbital apex (). No enhancement was noted on gadolinium enhanced T1 weighted axial image (). The internal structure revealed right oculomotor nerve within the cystic lesion, which continued into oculomotor cistern on oblique sagittal images with heavily T2-weighted 3D turbo spin-echo sequence ().\nThe patient underwent right sub-frontal craniotomy and the cystic lesion on prior MR images was shown after unroofing the optic canal. The cystic wall was fenestrated and high pressure cerebrospinal fluid -like fluid was drained. Microscopically, the cystic wall was lined by normal arachnoid membrane, representing arachnoid cyst (). After the operation, she felt immediate regression of symptoms on the third nerve palsy.