Indications

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  An occipital transtentorial craniotomy can provide excellent exposure for falcitentorial meningiomas and any lesion arising from the precentral cerebellar fissure, posterior incisural space, and adjoining structures.

Contraindications

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  Standard medical contraindications for prone positioning

  
  
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  Patent foramen ovale with positive bubble study for sitting position, owing to risks arising from venous air embolism

Planning and positioning

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  Standard preoperative magnetic resonance imaging (MRI) is needed as well as magnetic resonance venography or angiography to confirm patency of the straight sinus. Preoperative visual field testing is required as a baseline for all patients with larger tumors and greater risk of transient cortical blindness.

  
  

  
  

  
  

  

  
  

  
  

  For small tumors (<3 cm), a unilateral approach with the ipsilateral lobe down is sufficient. For most patients, a lateral or semilateral position is adequate. An approach from the right is preferred because a right hemianopsia, resulting from a left-sided approach, produces greater difficulty with reading. For the lateral position, using arm extension allows the shoulder to drop down avoiding collision of the chin with the clavicle. For larger patients, a modified park bench position is necessary.

  
  

  
  

  
  

  

  
  

  
  

  For larger tumors (>3 cm), a bilateral occipital transtentorial approach is needed. Patients can be placed prone or in the sitting position. Patients with a large body habitus benefit from the sitting position because high intrathoracic pressures in the prone position can complicate exposure.

  
  
  
  
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  Preoperative embolization is safe if the blood supply arises from external branches and the meningohypophysial branches of the internal carotid arteries.

  
  
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  The operating room setup may include bipolar cautery and bovie cautery, operating microscope (foot pedal for focus and zoom, mouthpiece for fine adjustments), chair with arm rests and floor wheels, and neurophysiologic monitoring with somatosensory evoked potentials.

  
  
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  Anesthesia includes 1 g of ceftriaxone, 10 mg of dexamethasone (Decadron), and 1 g/kg of mannitol on skin incision. Cerebral perfusion pressure should be maintained at greater than 70 mm Hg to prevent ischemia from brain retraction. Severe hypertension should be treated aggressively (e.g., propofol, thiopental, vasoactive drugs).

Procedure