Indications for Surgery
- Condition of patient: As a rule, the more normal the examination of a patient with an IMSCT, the better the patient will tolerate the surgery (10). Consequently, surgery is generally recommended at the time of first diagnosis before significant neurological deterioration begins to occur.
- Size of lesion: The lesion should be large enough to be easily found after a myelotomy has been performed. The author is reluctant to operate on lesions with diameters less than 1 cm and on lesions that do not cause enlargement of the spinal cord’s diameter.
Ideally several days should be taken to prepare the patient for surgery. Any relaxation of the surgical site that can be accomplished will improve the intraoperative monitoring and the tolerance of the surrounding spinal cord tissue to the surgical manipulations.
- Steroids: Time permitting, steroids should be administered for several days prior to surgery.
- Antibiotics: IV antibiotics are given at induction.
- IV steroids: Steroids are administered IV throughout the case.
The surgical outcome has become increasingly dependent on intraoperative physiological monitoring. Consequently, great care must be exercised in choosing and delivering anesthesia during the surgery.
- Constant infusion propofol: IOM requires a specialized anesthetic technique, particularly if muscle MEPs are to be used, and constant infusion propofol is currently the preferred anesthetic technique. Anesthesia has its greatest effect at the synapse, and the muscle MEPs require that the potential cross both the synapse of the upper and lower neuron and the neuromuscular junction. The propofol can be augmented with nitrous oxide if needed. It is important that bolus injections of any agent be avoided, if possible, as this will alter the amplitude of the potentials being recorded.
- IOM: IOM has been proven to decrease the incidence of loss of motor function due to surgery on IMSCT (40). If available, its use is highly recommended. If it is not available, consideration should be given to modifications of the techniques discussed below.
- Intraoperative ultrasound: Intraoperative ultrasound is useful for tailoring the extent of the laminectomy/laminotomy used for exposure of the tumor. It is also useful for localizing where the initial myelotomy should be performed, as it will allow for the localization of the main body of the tumor, its poles, and any cysts that may be present.
- Operative microscope: The operative microscope is another useful tool when operating on IMSCTs. It allows one to locate the median raphe and the approaching margins of the tumor when performing a central debulking of an infiltrating astrocytoma or ganglioglioma.
- Ultrasonic aspirator: The ultrasonic asopirator is helpful when performing a central debulking since its zone of activity is very shallow, causing minimal injury to surrounding tissue. It sucks the tissue it has liquefied away from surrounding tissue, thereby allowing for good visualization of the surgical bed.
- Contact lasers: Contact lasers such as the Nd:YAG can be very effective for contact cautery of pial vessels and cauterization of small pieces of tumor tissue that do not easily separate from surrounding normal tissue. They do have thermal spread, however, so they should be used conservatively at the extremes of the tumor’s margins.
- Fixation of lamina: Plates and screws (metal) or pins (resorbable) can be used to replace lamina at the completion of the surgery if a laminotomy was performed. Consideration should be given to the artifact they may create on subsequent MRI scans when selecting the materials to be used.