Indications

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  Indicated for lesions located within the fourth ventricle or brainstem that extend higher than the pontomedullary junction. The alternative approach has traditionally been the transvermian approach, where the vermis is split. This approach takes advantage of natural corridors without the risk of consequent neural deficits attendant on other techniques.

Contraindications

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  Cervical pathology that opposes neck flexion. To access the foramen magnum region the neck needs to be markedly flexed.

  
  
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  Diffuse lesions (e.g. diffuse pontine glioma). However, the telovelar approach may be used if a biopsy is required to establish an adjuvant treatment regimen.

  
  
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  Lesions located laterally at the pons and medulla may be better approached through a lateral approach (e.g. retrosigmoid, far lateral, extreme lateral, transpetrosal approaches) since the telovelar approach is ideal for midline lesions.

Preoperative Considerations

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  Anatomically, the approach provides visualization from the obex up to the cerebral aqueduct and to the lateral recesses of the fourth ventricle bilaterally.

  
  
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  In patients presenting acutely with symptomatic hydrocephalus, an intraventricular catheter is placed for judicious CSF drainage until the time of surgery.

  
  
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  Anesthetic considerations:

  
  
  
  
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    For resection of intrinsic brainstem lesions, the anesthesiologist should be advised to watch for signs of cardiovascular instability (i.e. HR, BP changes).

    
    
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    In situations where brainstem motor mapping will be performed, it is imperative that the patient’s body temperature is approximately 36.0–36.5 °C, the anesthetic minimum alveolar concentration (MAC) is no higher than 0.5 and muscle paralysis is not employed.

    
    
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    The anesthesiologist should also be advised to employ a NIM (nerve integrity monitoring) endotracheal tube for lower cranial nerve monitoring.

  
  
  
  
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  Neuromonitoring considerations:

  
  
  
  
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    Neuromonitoring is performed for cranial nerves V, VII–XII in addition to somatosensory evoked potentials.

    
    
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    For intrinsic brainstem lesions, motor evoked potentials are performed in addition to continuous electromyography throughout the tumor resection.

  
  

Surgical Procedure