TUMOURS OF BRAIN STEM
Brain stem tumours constitute about 5 to 10% of all intracranial tumours and are most common in childhood and adolescence. Gliomas are the most frequent type of tumour and the ratio of low to high grade gliomas is nearly 50:50. They usually infiltrate the brain stem and cause its enlargement. Some of the gliomas are circumscribed nodülar forms and in such a case an attempt at total removal of the nodule is an option for treatment (Fig. 3-143).
Various surgical approaches are used according to the exact size and location of the lesion. Caudal brain stem tumours are exposed through a midline or retromastoid suboccipital approach to the posterior fossa. The supratentorial occipital approach to the pineal region can be used also for lesions involving the ponto-mesencephalic brain stem.
The microsurgical technique of tumour removal with the use of the ultrasonic aspirator and laser is the widely accepted standard (Figs. 3-144; 3-145). Nodular tumours that have defined borders within the brain tissue should be removed till normal brain tissue is visible. In nodular tumour types surrounded by a wide zone of infiltration, a significant part of the tumour tissue is removed, but the infiltrated zone is left intact. In these cases the postoperative CT and MRI will reveal afterward small parts of residual tumour. In diffuse gliomas, when any border between the tumour and the brain tissue is absent under the microscope, the greater part of the tumour will remain on the follow-up CT and MRI images. The majority of brain stem gliomas are relatively avascular and bipolar coagulation is applied rarely and with extreme caution.
Immediately after surgery a relatively big number of the patients deteriorate in comparison to their preoperative focal deficit. However, follow-up for 2 to 3 months reveals an improvement and it may bring the patients to a better functional level than before surgery.
