Operative Planning

• Review imaging (magnetic resonance imaging [MRI], volumetric MRI)
  
• Three-dimensional (3D) reconstructions are performed with the frameless stereotactic system (optional)
  
• Patients selected for callosotomy usually undergo sectioning of the anterior four fifths of the corpus callosum; if seizures are not well controlled, these patients may be considered for a second-stage sectioning of the posterior corpus callosum (i.e., splenium)

Equipment

• Major craniotomy tray
  
• Mayfield head holder
  
• Self-retaining retractor system
  
• High-speed drill
  
• Frameless stereotactic system (optional)

Operating Room Set-up

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

Anesthetic Issues

• Hyperventilation to pCO₂ = 25 mm Hg
  
• Intravenous dexamethasone and antibiotics (cefazolin 2 g every 8 hours or vancomycin 1 g every 12 hours for adults) should be given 30 min prior to incision
  
• Intravenous mannitol 1 g/kg is administered prior to turning of the bone flap for brain relaxation
  
• The patient’s maintenance anticonvulsant medications are continued.

Positioning

• Patient supine with head lateral (right down) and fixed in Mayfield head holder, or patient in lateral position with head parallel to floor and elevated 10 degrees
  
• Vertex of head is tilted up 45 degrees and the head of the operating table is slightly elevated
  
• Fiducial markers are coregistered and the accuracy of the frameless stereotaxy is confirmed (if used)

Planning of Shave

• Use disposable razor
  
• A 3-cm wide strip (or less) along planned bicoronal incision is shaved

Sterile Scrub and Preparation

• A wide U-shaped dural flap is 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.
  
• Subdural adhesions from previous cranial injuries may be present and are carefully divided.
  
• The dural flap is reflected over the midline, not overturned, and then loosely secured with tacking sutures.

Approach to Corpus Callosum

• Protective strips of Telfa or Surgicel and Cottonoid patties are placed over the cortical surface of the right frontal lobe.
  
• The operating microscope is brought into the field.
  
• A 3-cm area for retraction is chosen on the basis of the draining veins.
  
• The arachnoid in the interhemispheric fissure is opened sharply.
  
• Irrigating bipolar cautery is used to divide arachnoid adhesions between the hemisphere and the sagittal sinus.
  
• Small bridging veins are judiciously divided to facilitate hemispheric retraction.
  
• The optimal trajectory is perpendicular to the skull surface.
  
• Dissection is continued inferiorly along the falx; tapered brain retractors are placed to maintain the interhemispheric corridor.
  
• The callosomarginal and pericallosal arteries may be 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.
  
• Pial integrity should be maintained during separation of the two cingulate gyri.
  
• Each of the paired pericallosal arteries is separated to either 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 the cingulate gyri.
  
• The dissection is continued to expose the genu and body of the corpus callosum.

Corpus Callosotomy

• Irrigating bipolar coagulation and suction are used to develop a callosotomy beginning at the anterior portion of the body.
  
• Section of the callosum is carried anteriorly through the genu and rostrum to the anterior commissure, which is left intact.
  
• The layers of the corpus callosum are successively traversed with cauterization and suction until the two leaves of the septum pellucidum are reached; ependymal vessels are cauterized to prevent bleeding into the ventricles.

Entry into the Lateral Ventricle

• The cauterized ependymal layer (septum) is preserved (when possible) to limit entry into the lateral ventricle.
  
• Additional brain relaxation is accomplished by drainage of cerebrospinal fluid, if necessary.
  
• The anterior limit of the callosotomy is determined by exposure of the anterior commissure by following the column of the fornix.
  
• Frameless stereotaxic guidance can be used to determine the adequacy of the posterior extent of the callosotomy, which should be the anterior 80% of the callosum.
  
• Alternatively, a Cottonoid can be laid into the callosotomy to measure its length accurately (relative to full length on MRI).

• The ventricles are irrigated and filled with warm saline.
  
• Meticulous hemostasis at each successive tissue layer encountered during exit from the lateral ventricle is achieved with bipolar cautery and hemo-static materials.
  
• The dura is closed in a watertight fashion with 4–0 silk sutures.
  
• A central dural tenting suture is placed, and the dura is covered with compressed Gelfoam.
  
• Bone flap is secured with titanium microplates.
  
• Galea is closed with inverted 3–0 Vicryl sutures.
  
• Skin edges are apposed with staples; Xeroform and head wrap are applied.

• Steroid taper begins on postoperative day 1
  
• Antibiotics continued for 24 hours
  
• Postoperative MRI to document the extent of the callosotomy (volumetric 3D in sagittal plane)