Operative Planning

• Review imaging; identify tumor location relative to normal parietooccipital anatomy
  
• Visual field examination
  
• Consider using visual functional magnetic resonance imaging (fMRI)
  
• For lesions of the parieto-occipito-temporal junction in the dominant hemisphere (i.e., angular gyrus), cortical mapping may be appropriate
  
• Plan the craniotomy to provide the shortest possible working distance between the tumor and the surface of the brain
  
• Measure the tumor in all three major axes and determine which side of tumor is nearest the visual cortex
  
• Note degree of edema and enhancement pattern of lesion on MRI
  
• Note presence of calcium or hemorrhage within the lesion on noncontrast computed tomography (CT) and MRI
  
• Note proximity and relation to sagittal and transverse sinus and deep draining veins
  
• To differentiate between enhancement because of recurrent tumor or enhancement due to radiation necrosis, consider use of specialized imaging of metabolic activity (positron emission tomography scan)
  
• Neuropsychological testing has been advocated by some experts as a means of delineating subtle deficits not apparent after neurologic examination
  
• Stereotactic set-up may be needed for small, poorly defined lesions in critical regions in neurologically intact patients

Special Equipment

• Ultrasonic aspirator

Occipital Approach

Tumor Resection

• For high grade lesions or recurrence with significant amount of edema, multiple burr holes are used for the craniotomy
  
• For low grade lesions with ill-defined margins on MRI, consider use of stereotactic localization for biopsy
  
• For lesions with a significant cystic component, initial stereotactic aspiration of cystic fluid for relief of mass effect is a consideration
  
• Cortical incision is made longitudinally away from the sulci to avoid unnecessary bleeding
  
  
  
  • Keep incision as short as possible; avoid subpial hemorrhage from excess retraction at edges and corners
    
  • Subcortical tissues spread in the long axis of the incision until the tumor is reached; do not resect white matter
    
  • Use intraoperative ultrasound and/or stereotactic probe in eloquent brain
  
  
• Initial debulking of tumor with irrigating bipolar cautery or ultrasonic aspirator is performed from its center to the periphery
  
• After initial relief of mass effect from the internal decompression, a subpial place is developed and maintained with Cottonoids in an effort to circum-scribe the tumor margins
  
• Diagnosis is confirmed with intraoperative review of frozen section by neuropathologist
  
• For high grade lesions, adjuvant therapies such as convection enhanced delivery of chemotherapeutics or implantation of Gliadel wafers may be considered prior to closure
  
• Hemostasis of the resection cavity is methodically achieved with bipolar cautery, Avitene, Surgicel, Gelfoam, or hydrogen peroxide–soaked cotton balls
  
  
  
  • This should be done at the anticipated postoperative systolic blood pressure
  
  
• Watertight dural closure, particularly if chemotherapy wafers are placed; dural graft may be required to achieve watertight closure, particularly in recurrent tumor surgery following radiation therapy