Indications for Procedure
- Control of symptoms due to mass: A posterior fossa lesion in a patient with signs and symptoms of elevated ICP is usually addressed surgically to remove the mass causing the symptoms.
- Hydrocephalus: Hydrocephalus requires emergent management (EVD or ETV) if it is prominent and the patient is unstable for posterior fossa surgery.
- Timing of surgery: Surgery is generally performed within 24 hours of obtaining the MRI of the brain and total spine. Patients with lethargy or rapidly progressive symptoms may require immediate operative intervention. Those without hydrocephalus and an indolent presentation may be treated more electively.
- Dexamethasone: Dexamethason is started on admission and should be continued with a bolus administered during anesthesia induction.
- Mannitol (0.5–1.0 g/kg): Mannitol can be administered during skin opening to further relax the brain.
- Elevated pressure within posterior fossa: A tight posterior fossa can be anticipated. Several measures can be taken to alleviate this problem. Mannitol (0.5–1.0 g/kg) is administered during skin opening. Fluid input and output should be kept roughly balanced during the surgery, and overhydration should be avoided. Mild hyperventilation with a target end-tidal pCO2 of approximately 30 mm Hg will also help.
- Dangers in positioning: Standard positioning for these cases requires flexion of the head with the patient in a prone position. Normal airway pressures and bilateral, symmetrical ventilation must be confirmed after final positioning to ensure that the endotracheal tube has not kinked or descended down the right mainstem bronchus.
- 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.
- Intraoperative neurophysiological monitoring: This is controversial and not used by all neurosurgeons for these cases. It is most useful in patients with lateral tumors involving the cerebellopontine angle or tumors with involvement of 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 is mandatory for safe resection of these tumors.
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