Preparation for Surgery for Medulloblastomas in Children
Indications for Surgery
Presence of posterior fossa mass: Newly diagnosed posterior fossa tumors suggestive of medulloblastoma on imaging studies require timely surgery to treat obstructive hydrocephalus, confirm the pathological diagnosis, and reduce the tumor burden as much as possible.
Timing of surgery: The tumor is generally operated on shortly after MRI scans of the brain and total spine are obtained. Patients with lethargy or rapidly progressive symptoms may require immediate operative intervention, whereas those without hydrocephalus and an indolent presentation may be treated more electively.
Admission to ICU: Children with medulloblastomas are at high risk for experiencing pressure waves and herniation. Therefore, until surgery is performed, they should be in a setting where they can be monitored closely for neurological changes.
Dexamethasone: Dexamethasone is started on admission and should be continued with bolus administered during anesthesia induction.
MRI of brain and spine: Patient condition permitting, these images should be obtained preoperatively.
Elevated pressure in posterior fossa: A tight posterior fossa can be anticipated. Several measures can be taken to lessen the pressure. Mannitol (0.5–1.0 g/kg) is administered during skin opening. Mild hyperventilation with target end-tidal pC02 of approximately 30 mm Hg will also help and will keep the I/O ratio roughly balanced during surgery.
Dangers in positioning: Standard positioning for these cases requires flexion of the head while it is in prone position. Normal airway pressures and bilateral, symmetric ventilation are confirmed after positioning with neck in flexion.
Vascular access: All patients should have an arterial line and appropriate venous access to prepare for blood loss, which may be rapid and life-threatening during dural opening and/or tumor resection, especially in young children. Coagulopathy and thrombocytopenia should be ruled out and aggressively corrected in the event of extensive blood loss.
Devices to Be Implanted
Intraoperative neurophysiological monitoring: The use of intraoperative neurophysiological monitoring is controversial, and not all neurosurgeons employ such monitoring for these cases. It is most useful in patients with lateral tumors that involve the cerebellopontine angle or tumors that involve the brainstem.
Intraoperative ultrasound: This tool is useful for identifying echogenic tumor prior to resection and then confirming absence of echogenic tumor at the conclusion of tumor resection.
Operative microscope: The use of the operative microscope has become ubiquitous, and many consider it mandatory for the safe resection of these tumors.
Ultrasonic aspirator: The ultrasonic aspirator is helpful to rapidly decompress tumor once the brainstem has been identified and protected.