Some major subarachnoid cisterns:
Cerebellomedullary cistern (Cisterna magna)
Pontine cistern (Prepontine cistern or cisterna pontis)
Cerebellopontine cistern (Angle cistern or cerebellopontine angle cistern)
Interpeduncular cistern (Cisterna interpeduncularis or chiasmatic cistern)
Superior cistern, quadrigeminal cistern, ambient cistern or cistern of the great cerebral vein
For petroclival tumors, first the posterior fossa cisterns are opened to drain the cerebrospinal fluid and relax the brain. The tentorium is divided posterior to the trochlear nerve, and the anterior part is excised.
The Meckel's cave is opened widely to relax the trigeminal root. Tumor resection is then performed with bipolar cautery, micro-scissors, and the ultrasonic aspirator, working toward the base of the tumor, and working from below upward, to identify and avoid injury to the abducens nerve. The posterior cavernous sinus can be opened if the tumor extends into it. If the tumor is well above the tentorial notch, a transsylvian approach is performed at the same sitting 1).