The basis for the surgical management of meningiomas was presented in the classic two-volume work Meningiomas by Harvey Cushing and Louise Eisenhardt. The initial evaluation of a patient with a meningioma should include a careful evaluation of the history and clinical findings. For many patients the only radiographic study needed is a magnetic resonance imaging (MRI) scan. Computed tomography (CT) is obtained when information is needed about bone detail. Angiography is used when embolization is a consideration and in those patients in whom more information is needed about the arterial supply or venous drainage than can be obtained from MRI or MR angiography (MRA).
The treatment options of surgery, radiation therapy. or a combination of the two, or observation with periodic clinical and MRI evaluations are considered. The physician must understand what the patient's expectations are from the treatment program and to consider carefully the short- and long-term benefits and risks. In many patients an operation is clearly indicated because of increasing disability, radiographic documentation of a surgically treatable tumor, and an assessment that this treatment can be done with an acceptable risk. However, in some patients the management decision can be difficult because of minimal or nonprogressive symptoms, the indolent natural history of some meningiomas, the risks involved with treatment because of location or pathologic anatomy, the development of new radiosurgery treatments the longterm results of which are still unknown, and the incidental finding of an asymptomatic tumor.
The objective of the operation is total removal of the meningioma, including the involved dura and bone, if at all possible. The completeness of surgical removal of the tumor is the single most important prognostic factor. However, this goal must always be tempered by surgical judgment which considers that the first priority is to preserve and improve function. In some patients, in whom total removal carries a significant risk of morbidity, it is better judgment to leave some tumor and plan to follow the patient with clinical evaluation and MRI studies, perform a further operation at a later time, or use radiation therapy, as indicated.
The patient is given steroids for at least 48 h before surgery and longer if there is considerable edema in the adjacent brain tissue. This is important in helping prevent the problems with cerebral edema that may follow removal of a meningioma. The neurosurgeon should have available an anesthesiologist who is knowledgeable in the field of neurosurgery. The operating room should be dedicated to neurosurgery and include the availability of trained personnel, operating microscope, bipolar coagulator, laser, and Cavitron ultrasonic surgical aspirator. The recovery room and intensive care unit should be staffed with personnel familiar with neurosurgical problems.
When the patient arrives in the operating room, In some cases, a radial artery catheter is inserted for continuous monitoring of blood pressure and evaluation of blood gases. The Pco2 is kept near 30 mmHg during the operation. Thigh-high alternating pressure boots are placed.
A smooth induction of anaesthesia without the patient straining or coughing and careful control of blood pressure are important factors in getting the surgery off to a good start. An indwelling Foley catheter is inserted. As soon as this is done the patient is given 10 to 20 mg of furosemide. During the preparation and exposure, a 20 percent solution of mannitol is given in a dosage of I to 1.5 g/kg over 20 to 30 min. Prior to making the skin incision, an antibiotic, usually a cephalosporin, is administered and is continued until 24 h after surgery.
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.
Steroids are continued for several days and then gradually tapered. Anticonvulsants are given to patients with supratentorial meningiomas for up to 3 months. but longer if there is a history of a seizure. Thigh-high alternating pressure boots that were placed prior to operation are continued until the patient is ambulatory. If there is evidence of worsening in the patient's condition postoperatively. a CT scan is done to look for hematoma. cerebral edema. and hydrocephalus. The finding of cerebral edema may require increased steroids or intermittent mannitol administration.
If the meningioma can be removed totally by surgery. the recurrence rate is low. Even if total removal is not possible. no further immediate treatment may be indicated. Many meningiomas are so slow-growing that they cause little trouble over many years. When recurrence develops. the treatment for many patients is operation. Usually recurrent meningiomas do not change their basic histologic characteristics. The demonstration of hormonal binding in some meningiomas suggests that a trial of chemotherapy be considered for some recurrences" but the effectiveness of this treatment has not been demonstrated.
Radiation therapy has been shown to arrest the growth of some meningiomas. External-beam therapy and radiosurgery with a gamma unit or linear accelerator have both been reported to be effective. The indications for their use have included residual tumor left at operation. tumor recurrence. a meningioma that could not be treated surgically. and malignant pathology.
Not every patient with a meningioma needs treatment. In some patients. periodic clinical evaluation and MRI is an appropriate course to follow. Observation is indicated in asymptomatic patients with little or no edema in the adjacent brain. patients with mild or minimal symptoms or those with a long history. older patients with a seizure or very slowly progressing symptoms. patients in whom treatment carries a significant risk. and patients who make the decision after being presented the treatment options.