Imaging

• Computed tomography: isodense to hyperdense round cyst in the third ventricle with or without obstructive hydrocephalus
  
• Magnetic resonance imaging (MRI): cyst of variable intensity, usually hyperintense on T1; in the third ventricle; may enhance with contrast; size of ventricles is important factor in determining approach; assess cortical veins on contrast images or magnetic resonance venography if planning an interhemispheric transcallosal approach

Surgical Approach

• Choice based on ventricular size, surgeon experience, and goals of operation
  
• Transcortical
  
  
  
  • Advantages: direct route to lateral ventricle, especially accessible if ventricles are dilated; ability to widen cortical opening to minimize frontal lobe retraction; if ventriculostomy already in place, may follow tract down to ventricle
    
  • Disadvantages: substantial amount of frontal lobe traversed, especially if ventricles are small; postoperative porencephalic cyst in the frontal lobe with a potential persistent cerebrospinal fluid (CSF) tract
  
  
• Transcallosal
  
  
  
  • Advantages: relatively minimal dissection through white matter compared to transcortical approach; straight trajectory down to third ventricle
    
  • Disadvantages: need to have complete or partial exposure of the sagittal sinus with potential for bleeding; risk of sinus occlusion with retraction; exposure may be restricted by bridging veins from frontal lobe into sagittal sinus
  
  
• Endoscopic
  
  
  
  • Advantages: minimally invasive with minimized incision, blood loss, and hospital stay; minimal retraction on the frontal lobe
    
  • Disadvantages: difficulty in obtaining complete excision of cyst wall if adhered to surrounding structures; difficult to open roof of third ventricle if foramen needs to be enlarged; access to small ventricles is difficult without stereotactic navigation

• Mayfield head holder
  
• Craniotomy tray with microdissectors and micromirror
  
• High-speed drill
  
• Retractor system (Budde halo, Greenberg retractor, or Yasargil)
  
• Bipolar cautery

Endoscopic Equipment

• Rigid endoscope
  
• Endoscopic biopsy cup forceps, suction, bipolar and/or monopolar cautery, microscissors

Operating Room Set-up

• Frameless stereotactic navigation if needed for ventricular access
  
• Ultrasound if needed for guidance toward ventricle in transcortical approach
  
• Microscope
  
• Sitting stools if needed
  
• Endoscopy: video monitors at foot of bed

Anesthetic Issues

• Preoperative antibiotics within 30 min of incision
  
• Intravenous steroids (dexamethasone)
  
• Arterial line
  
• Precordial Doppler for transcallosal approach

Transcortical

Transcallosal

• Nondominant side is preferred
  
• Position patient supine with head flexed and neutral rotation or turned slightly to the left
  
• Modified bicoronal incision slightly anterior to the coronal suture from right temporal region to left superior temporal line
  
• Plan craniotomy that straddles the coronal suture with two thirds anterior to it and one third posterior
  
• Craniotomy also extends over superior sagittal sinus
  
• Burr holes on both sides of the midline to allow for complete freeing of the bone from the sinus. Ensure that cuts adjacent to sagittal sinus are performed last.
  
• Place Surgicel and Gelfoam with thrombin in strips along sagittal sinus to control bleeding
  
• Dural incision with a flap toward the sinus
  
• Suture the dural flap to the other side, but without too much tension to avoid occlusion of the superior sagittal sinus
  
• Identify bridging veins and dissect arachnoid around them if needed to mobilize them. Veins anterior to the coronal suture can be coagulated and divided in order to provide wider corridor of dissection.
  
• Begin frontal lobe retraction, allow CSF to be released from interhemispheric fissure for gradual relaxation of the brain
  
• Place retractors on frontal lobe and on falx
  
• Identify the corpus callosum and pericallosal arteries, which are retracted laterally
  
• Opening of 2 to 3 cm into the corpus callosum
  
• Identify which lateral ventricle has been entered by locating landmarks, such as the septal vein, choroid plexus, and foramen of Monro
  
• Microdissection of the colloid cyst as described above
  
• Need watertight dural closure