[Orbital schwannoma developing from the superior branch of the oculomotor nerve--case report].

Orbital schwannoma accounts for 1-6% of all orbital tumors and it is not easy to identify the origin of the tumor because of the anatomy of the orbit. A case of orbital schwannoma developing from the superior branch of the oculomotor nerve is reported. A 74-year-old female was admitted to our hospital with the chief complaint of left exophthalmus. MR imaging revealed a space-occupying lesion in the left orbit. Operation was performed through the transcranial approach. It was noticed that the tumor was developing from the nerve that runs into the superior rectus muscle or the levator palpebrae superioris muscle, and it was diagnosed as a schwannoma on frozen section histology during surgery. The tumor was successfully removed and, postoperatively, no additional defects occurred. Careful consideration of microsurgical anatomy is essential for surgery of orbital schwannoma especially when it's necessary to cut the nerves.