After careful positioning, the patient's head is held with the three-point skeletal fixation headrest. Care is taken to keep the head above the heart level and to avoid compression of the jugular veins in the neck. The position must take into account the effects of gravity, the need to minimize brain retraction, and the avoidance of compression of the brain against the edge of the dura. If the head is to be well elevated or a semisitting position is used, a central venous pressure line is placed in the right atrium, using x-ray guidance. Some type of magnification (either loupes or the operating microscope) is used for the entire operation. The skin incision must allow for full exposure of the tumor. Blood supply to the scalp flap must be adequate. and a wide enough base must be left to provide good vascularization. The cosmetic result of the scar and bone flap should be considered. The pericranial tissue is left attached to the back of the scalp flap so it can be taken at the end of the operation to repair any dural defects. A free bone flap will allow wide. expeditious exposure of tumor and can be easily enlarged if necessary. Blood supply coming through the bone is occluded. At the end of the operation the bone flap is wired solidly in place. If burr holes or bone removal due to tumor will leave a cosmetic deformity or a large bone defect. a cranioplasty is done. For a burr hole or small bone defect, the area is filled with acrylic or bone dust harvested during burr hole production.
Bleeding from the dura is controlled with bipolar coagulation. Surgicel or Gelfoam. The dura is held to the inner table of bone along the craniotomy opening with sutures placed from dura to pericranial tissue or into holes drilled in the bone.
For superficial meningiomas the dura is opened at the margin between brain and tumor. One should always try to expose as little normal brain as possible. especially when the brain is still full because of the presence of a large tumor mass. All dura attached to the tumor is eventually removed. but in convexity and parasagittal meningiomas it is usually wise to leave it attached to help in retraction. At the end of the operation the convexity dura is replaced with a graft of pericranial tissue which is taken from the back of the scalp nap.
Everything is done to avoid retraction or removal of adjacent brain tissue. In many patients it is best to carry out an extensive internal decompression of the tumor prior to trying to dissect the capsule. The decompression is facilitated by use of the ultrasonic aspirator or cautery loops. Bleeding from within the tumor will often cease spontaneously. but in some cases bipolar coagulation or Surgicel may be needed. Gentle pressure is placed against the capsule of the tumor or on the dural attachment to help define the plane with adjacent brain tissue. Brain tissue is gently separated from the capsule of the tumor using fine dissectors. As blood vessels between capsule and brain tissue are encountered. they are coagulated with bipolar coagulation and cut with microscissors.
The overall operative mortality in supratentorial meningiomas is less than 1 percent. Malignant meningiomas are considered separately.