The patient came to the clinic 21-November-2007 complaining of decreased hearing of the right ear with diplopea for 45 days duration.

On examination: the patient had left sided weakness and paresis of the right abducens nerve.

MRI performed 2005 showing dermoid of the posterior fossa and she was advised to wait and see. It was explained to the patient, that the sooner the better it is to perform surgery, since every loss in her neural functions, it will be hard to regain after surgery. The patient was admitted 24-November-2007 to Shmaisani hospital and new MRI was performed, which showed increase in the dimensions of the tumor. Most of the tumor was located in the left side, but the patient was complaining from the right abducens nerve and had left sided hemiparesis.

With the setting position and TIVA and using Inomed Highline ISIS IOM with HSG KHBW scenario, posterior osteoplastic midline craniotomy with the flap attached to the C1 lamina, was performed and the flap reflected down near C2 spinous process. The dura was opened in V-shaped fashion and the upper edge was stitched to the upper border of the bony defect. The arachnoid of the cisterna magna was opened and the cistern, which was full of epidermoid was evacuated and that part, which was reaching the C2 level was decompressed and removed completely. The medulla was shifted to the left and the callamus screptorius was distorted and exposed to the field. It was possible to see the lower half of the floor of the fourth ventricle. Further removal of the tumor was achieved around the left PICA and left vertebral artery and the atrophied hypoglossal and accessory rootlets and the vagus. They were preserved, even with their tiny feeders. The removal was continued forward until the petrous bone came to view and the vein of Dandy was preserved with the shifted acoustico-vestibular and facial nerves with the ability to remove the expanding part supratentorially in the left side. The trigeminal nerve was preserved. The Hollow traction system was applied only for the left cerebellar lobe, and no constant traction was applied to the brainstem to avoid possible traction injury. The left vertebral artery and the basilar arteries were stuck to the distorted brainstem. This was advantageous, since the clinically manifesting part was separate from the rest of the mass. That part was opened and the epidermoid material was evacuated separately, decompressing the right clival region from the left lower angle of the field. The clivus was inspected and it became free of any remnants, except for 0.5 mm thickness of a carpet which was thought that it could be attached to tiny major atrophied neural structures. Another small fragment at the projection of the left cochlear nuclei 0.2 X 0.3 mm was left attached to a running vein, which could lead to venous problems. No any bleeding or problems happened during the surgery and her husband Dr. Ayed Haddad a general surgeon, was present in most of the stages of the operation.

All the data of the iom were steady and without any changes from the start of the surgery until the end. It was possible to communicate with the patient in certain stages of the operation. Water-tight closure of the dura and Lyodura was used to obtain this tight closure.
The bony flap was reflected to place and the bony dust harvested during craniotomy was gathered and used to fill the prominent bur holes.

Routine closure of the wound and immediate smooth postoperative recovery of the patient with no neurologic deficit.
 

IOM is a very strong tool to avoid and prevent possible catastrophic events, especially in minefield area such in this case.

BrainLab and intraoperative MRI are good options to use and they will be installed within the next year, but in this case, iom is more important, since there are a plenty of anatomical landmarks, which guide the surgeon and make him sure what he is doing.