The Operation for Dorsally Exophytic Gliomas of the Brainstem in Children

Surgical Approach

• Midline craniotomy +/- laminotomy: A midline suboccipital craniotomy with or without a C1 laminotomy is used to access dorsally exophytic brainstem gliomas.
• Obtain baseline IOM: Before the CNS is entered, a complete set of baseline IOM potentials should be obtained.
• Cerebellar incision if fourth ventricle exposure required: For cervicomedullary tumors whose rostral portion is covered by the caudal cerebellum, a transvermian or telovelar approach is used to access the medulla and caudal fourth ventricle.

Intervention (Resection)

• Decompress enlarged ventricles: In patients with findings consistent with an obstructive hydrocephalus who have not previously undergone a CSF diversion procedure (e.g., ETV or ventricular shunting), placement of an EVD via an occipital bur hole may be considered.
• Obtain specimen to determine grade of tumor: Specimens should be sent early for analysis by frozen section. Identification of a high-grade lesion is an indication to halt the surgery, as there is no proven long-term benefit to debulking aggressive lesions.
• Resect extraaxial portion in ventricle: Resection of the tumor takes place primarily within the fourth ventricle using the ultrasonic aspirator or suction-aspiration.
• Conservative approach to intraaxial portion of tumor: If there is a large intramedullary component to the tumor or if it is felt that damage to the functional tissues of the brainstem would be unavoidable, subtotal resection should be attempted. Some have advocated that resection carried to the level of the floor of the fourth ventricle confers a sufficient balance between disease control and preservation of neurological function by minimizing the risk of injuring functional brainstem tissues.
• Maintain orientation during resection: During the debulking of the tumor, constant visualization of the floor of the fourth ventricle is critical, as the nuclei and/or tracts of CN VI, VII, X, and XII exist superficially in the dorsum of the brainstem and are at risk for injury with overly aggressive retraction and tumor debulking.
• Maintain awareness of IOM: Ongoing communication should be maintained with the IOM personnel while working within the brainstem to minimize the risk of neurological injury.
• Avoid cautery: Use of electrocautery should be avoided as the surgeon reaches the tumor margins to minimize potential injury to functional tissue.

Closure

• Primary closure of dura: Primary closure of the dura in a water-tight fashion is preferred. Grafting with a dural substitute can be performed as needed.
• Replace bone when possible: If possible, the bone from the craniotomy and laminotomies should be replaced using plating or sutures.
• Fascial closure important: Fascial closure should be water-tight as this is the layer that prevents CSF leakage.
• Drains: Surgical drains are typically not placed postoperatively unless there is concern for inadequate hemostasis during closure.