Operative Planning

• Review imaging (magnetic resonance imaging [MRI])

Equipment

• Major craniotomy tray
  
• Mayfield head holder
  
• High-speed drill
  
• Frameless stereotaxy (optional)

Operating Room Set-up

• Headlight
  
• Loupes (optional)
  
• Bipolar cautery and Bovie cautery
  
• Microscope

Anesthetic Issues

• Degree of intracranial pressure elevation is communicated to anesthesiologist
  
• Hyperventilation to pCO₂ = 25 to 30 mm Hg
  
• Intravenous dexamethasone and antibiotics (i.e., oxacillin 2 g or vancomycin 1 g for adults) should be given 30 minutes prior to incision

Sterile Scrub and Prep

Dural Opening

• U-shaped dural flap based medially along sagittal sinus
  
• During elevation of the dura, microdissection is used to preserve pial integrity and avoid injury to cortical draining veins and pacchionian granulations
  
• The dural flap is reflected over the midline but not overturned, and then loosely secured with tacking sutures so that sagittal sinus occlusion is avoided
  
• Place ventricular drain into lateral ventricle through middle frontal gyrus if hydrocephalus is present

Approach to Corpus Callosum

• Protective Telfa strips are placed over the cortical surface
  
• The arachnoid in the interhemispheric fissure is opened sharply
  
• Irrigating bipolar cautery is used to divide arachnoid adhesions between the hemisphere and sagittal sinus
  
• Small bridging veins are judiciously divided to facilitate hemispheric retraction
  
• The optimal trajectory to the lesion is considered, based on the MRI, and identified, based on the location of the coronal suture
  
• Dissection is continued inferiorly along the falx; brain retractors are placed to maintain the interhemispheric corridor
  
• The callosomarginal and pericallosal arteries are encountered during the approach to the corpus callosum; although it is not necessary to identify the callosomarginal arteries, they should not be mistaken for the pericallosal arteries
  
• The pericallosal arteries are separated to each side or moved together to one side; the corpus callosum is easily identified by its pearly white color
  
• The self retaining retractors are checked to prevent excessive retraction of the sagittal sinus or cingulate gyri

Corpus Callosotomy

• Irrigating bipolar coagulation and suction are used to develop a callosotomy measuring ~1 × 2 cm
  
• The layers of the corpus callosum are successively traversed with cauterization and suction until the gray ependymal lining of the lateral ventricle is reached; the vessels of the ependymal lining are thoroughly cauterized to prevent bleeding into the ventricles

• The cauterized ependymal layer is opened for entry into the lateral ventricle
  
• The brain retractor is repositioned just beyond the inferior callosal margin
  
• Orientation of entry into either the right or left lateral ventricle is confirmed by the configuration of the choroid plexus and thalamostriate vein, which course anteriorly in a medial direction to reach the foramen of Monro. Access to the right lateral ventricle after inadvertent entry into the left lateral ventricle is accomplished by further lateral resection of the corpus callosum or fenestration of the septum pellucidum.
  
• Release of cerebrospinal fluid (CSF) following entry into the lateral ventricle may result in a pressure gradient that displaces the septum pellucidum to the ipsilateral side; obstruction of the operative field is prevented by a generous fenestration and coagulation of the septum

Entry into the Third Ventricle

• Foraminal entry via the foramen of Monro, especially if it has been dilated by the presence of hydrocephalus, is the least traumatic; the choroidal fissure can be opened posteriorly to enlarge the foramen of Monro further
  
• If the lesion is inaccessible via foraminal entry, interforniceal approach is used
  
  
  
  • The interforniceal approach is facilitated by a callosotomy that is as close to the midline as possible
    
  • Identification of the interforniceal raphe is critical; this is accomplished by division of the septal leaves or, if they are fused, coagulation of the septum down to the level of the forniceal bodies
    
  • The interforniceal raphe is sharply divided from the foramen of Monro posteriorly for a maximum distance of 2 cm to avoid damage to the hippocampal commissure

Closure

• The resection cavity and ventricles are irrigated and filled with warm saline
  
• Patency of CSF drainage pathways is confirmed by passage of a microinstrument through the foramina of Monro and inspection of the third ventricular outlet into the cerebral aqueduct
  
• Meticulous hemostasis at each successive tissue layer from the ventricle to the hemisphere is achieved with bipolar cautery; hemostatic materials are minimized
  
• A ventricular catheter may be left in the lateral ventricle and tunneled under the flap
  
• Dura is closed in a watertight fashion with 4–0 silk sutures
  
• A central dural tenting suture is placed and dura is covered with dural substitute duraplasty (Duraform/DuraGen)
  
• The bone flap is secured with titanium microplates
  
• Galea is closed with inverted 3–0 Vicryl sutures
  
• Skin is closed with staples
  
• Xeroform and head wrap are applied

Postoperative

• Steroid taper begins on postoperative day 1
  
• Continue antibiotics until external ventricular drain is removed