Operative Planning

• Review imaging
  
  
  
  • Computed tomographic (CT) scan
    
    
    
    • Location of fourth ventricular clot in the setting of subarachnoid hemorrhage, especially without supratentorial blood and blood primarily in the cerebellar pontine angle
      
    • Degree of calcification in the setting of large and giant unruptured aneurysms
    
    
  • Magnetic resonance image (MRI): helpful in identifying intraluminal thrombus in the setting of large and giant unruptured aneurysms
    
  • Angiogram of PICA
    
    
    
    • Relationship of the aneurysm to the origin of PICA: the aneurysm generally will have its neck at the origin of PICA but on occasion may involve PICA itself either alone or in addition to the vertebral artery
      
    • Identify dominance of vertebrobasilar system: usually the aneurysm is on the dominant vertebral, but occasionally it may arise from the nondomi-nant vertebral or even vertebral ending PICA
      
    • Relationship of the caudal loop of PICA to the foramen magnum when dealing with distal PICA aneurysms
      
    • Nonsaccular aneurysms or wide-necked sessile aneurysms may often represent dissections and should be carefully reviewed because direct clip reconstruction is often more dangerous and no more efficacious than endovascular stenting or coiling
    
    
  • Angiogram of vertebrobasilar junction
    
    
    
    • Note the rostral-caudal location of the vertebrobasilar junction: usually these aneurysms can be reached via a far lateral suboccipital approach; combined presigmoid–far lateral approach should be considered (with or without division of the nondominant sigmoid sinus depending on the projection of the aneurysm)
      
    • Note the side of the confluens from which the neck of the aneurysm emanates: these lesions should always be approached from the side to which the aneurysm projects

• Coarse diamond drill bit for removal of the occipital condyle; alternative is the small matchstick (Midas Rex bit no. AM8)
  
• Fishhooks
  
• Micro-Doppler
  
• May need bypass tray, especially in case of distal PICA aneurysm where PICA sacrifice might be considered and in some cases may be augmented by PICA-PICA side-to-side anastomosis
  
• Radiolucent Mayfield head holder if intraoperative angiography

Operating Room Set-up

• As for acoustic neuroma
  
  
  
  • A left-handed surgeon will have the nurse at the head for a right-sided approach with the assistant between them and the microscope base off to the surgeon’s right, next to the patient’s abdomen
    
  • A right-handed surgeon will place the nurse to the right at the patient’s abdomen and the microscope stand at the patient’s head with the assistant in between

Anesthetic Issues

• As for anterior communicating (ACOM) artery aneurysm
  
• Brain stem auditory evoked responses (BAERs) add little, and stimulation of the lower cranial nerves had not been a useful adjunct

Spinal Drain

• For subarachnoid hemorrhage (SAH) cases (regardless of the presence of ventricular drain)
  
• In the case of a poor dural closure, this drain may be left in for 24 hours to facilitate wound healing

Positioning

• For most patients, lateral position is best for easier exposure of bony midline and condyle
  
• Shoulder roll with the head turned may be reasonable alternative in some cases
  
• With either lateral or supine positioning flex the neck to open atlantooccipital space and increase light to operative field
  
• Head/shoulder should be above the heart
  
• Shoulder should be taped down with care to avoid upper trunk injury

Far Lateral Suboccipital Craniotomy

• Goal
  
  
  
  • Early identification of the proximal vertebral artery
    
  • Lateral to medial line of site
    
  • Generous access to cerebellar hemisphere for retraction
  
  
• Steps
  
  
  
  • Curvilinear incision beginning over the cerebellar hemisphere and extending from the sigmoid-transverse junction medially to midline, leaving a dural cuff for closure and inferiorly to the arch of C2
    
  • Spinal drainage and/or opening of the cisterna magna will relax the cerebellum
    
  • Placement of dural tracking sutures sewn to the fishhooks to rotate the lateral dura maximally without compromising the sinus

Placement of Cerebellar Retractors

• Goal
  
  
  
  • Proximal control
    
  • Visualization of aneurysm
  
  
• Steps
  
  
  
  • Cover inflamed cerebellum with Surgicel; for unruptured aneurysms, this is not necessary
    
  • Fitting of two retractors: one from above to lift tonsil (useful early in dissection), one from medial to retract flocculus (useful late in dissection)
    
  • Use only one retractor at a time and give consideration to temporary vertebral artery occlusion and/or dissection of the clot from the cerebellum, to be retracted to prevent early rupture

Identification of Parent Vessel

• Goal
  
  
  
  • Exposure of the aneurysm for clipping
  
  
• Steps
  
  
  
  • Find vertebral artery as it enters the dura
    
  • Prepare segment for temporary clip

Identification of Aneurysm Neck