The Operation for Subependymal Giant Cell Astrocytomas in Children

The goal of surgery is to resect the SEGA and open up the CSF pathways at the foramen of Monro. There are two basic approaches to resect a SEGA: a transcortical, frontal approach to the lateral ventricle or an interhemispheric, transcallosal approach.

Patient Positioning

  • Supine: In the transcallosal procedure, the patient is positioned in a supine, straight position, with the head elevated by 15 degrees and flexed by 15 degrees.
  • Head holder: The head can be supported on a horseshoe headrest or a Mayfield clamp, depending on the choice of the surgeon. In infants and children younger than 3 years of age, in whom standard pin fixation cannot be used, the head could be positioned on a horseshoe headrest using a ‘U-drape’ to fix the head to the headrest (1).

Surgical Approach

The surgical approach depends upon tumor extension and the presence of associated hydrocephalus, but, above all, the surgeon’s experience.

  • Scalp incision: A bifrontal or unifrontal parasagittal flap inside the hairline, two thirds in front and one third behind the coronal suture, is standard.
  • Craniotomy: The bone flap should be at least 5 cm in size, medially touching the midline if an interhemispheric transcallosal approach is planned so that adequate space between bridging veins is available to reach the corpus callosum. A preoperative sagittal MRI may be useful to find adequate space to approach by looking at the bridging veins. Rarely, venogram may be required for identification.
  • Dural opening: The dura should be opened in a C-shaped manner based on the superior sagittal sinus, taking care to avoid injury to the bridging veins and the lateral wall of the sagittal sinus.
  • Interhemispheric approach: Many consider this the better approach to the ventricles. It gives access to both the lateral ventricles and the third ventricle while avoiding cortical brain tissue. It can be used easily even in the absence of ventriculomegaly. Entry should be at the interhemispheric fissure between two bridging veins. Care must be taken to avoid sacrificing the bridging veins, especially behind the coronal suture. The corpus callosum is split to a maximum of 2 cm between the anterior cerebral arteries.  
  • Transcortical approach: While this approach gives the surgeon direct access to the tumor, it does cause some direct trauma to the brain with resultant risk of postoperative seizures and occasional dysfunction (attention deficits or significant speech problems with dominant hemisphere lesions). .

Intervention

  • Piecemeal removal: The goal for resection should be complete removal of the tumor when possible. Removal is carried out so as to reestablish the patency of the foramen of Monro (27). The tumor is removed in a piecemeal fashion, without damage to the fornix.
  • Ventricular drain: If there is doubt about bleeding and foraminal patency, a ventricular drain is generally left inserted to aid recovery.
Operative view of a SEGA: Exposure was via a transcallosal approach

 

Closure

  • Final hemostasis of resection cavity: The resection cavity can be temporarily lined with Surgicel to aid in hemostasis. The cavity is gently irrigated with lukewarm saline. The Surgicel is removed once hemostasis has been established to prevent any blockade to CSF flow.
  • Placement of EVD: EVD is considered if there is persistent unexplained oozing from the cavity or if there is a concern about postoperative hydrocephalus.
  • Closure of callosal opening: After the tumor is removed, the callosal opening may be covered with gel foam. This usually suffices, but fibrin glue can be used to hold the gel foam in place. These steps are considered since a persistent fistula can create an intractable subdural effusion.
  • Bone flap: The bone flap is replaced after primary watertight dural closure.
  • Scalp: The skin is approximated with sutures or skin staples.