The Operation for Focal Tumors of the Brainstem in Children

Surgical Approach

• Midbrain: Midline and dorsal tumors can be approached via a suboccipital or supracerebellar approach. Rarely, they can also be approached via the third ventricle. The more ventral and lateral tumors are commonly operated on via the subtemporal approach.
• Pons and medulla: These tumors are typically approached from the midline. The incision is typically in the midline from the inion to the lower limits of the tumor. A suboccipital craniotomy is performed for exposure of the extent of the tumor with the removal of the cervical lamina as needed.
• Dural opening: The dura is typically opened in a Y-shaped fashion
• Initial approach: A telovelar approach to the floor of the fourth ventricle is most often used, although transvermian incisions can be used for tumors lower in the fourth ventricle. Mapping of the cranial nerve nuclei and tracts should be performed before entry into the brainstem. This entry should be planned for a safe, electrically silent zone.

Intervention

Endoscopic biopsy

• Transventricular allowing visualization of biopsy site: Open biopsy or resection of intrinsic midbrain lesions may be associated with high morbidity (36). Transventricular tumor biopsy with an endoscope may be performed with or without CSF diversion when the brainstem tumor is adjacent to the walls of the third ventricle (42). This is a minimally invasive method to obtain the precise diagnosis.
• At time of ETV: For biopsy associated with ETV, a bur hole is placed more anteriorly than the conventional ETV location.  ETV should be performed before the biopsy to ensure adequate CSF diversion, as bleeding from the biopsy may obstruct the view and render ETV difficult if performed after tumor biopsy (43).

Stereotactic biopsy

• Stereotactic biopsy for deeper lesions: Stereotactic biopsies may be considered for lesions that cannot be approached with neuroendoscopy in which accurate histological diagnosis is warranted but more aggressive surgical resection is deemed unsafe.

Open surgical resection

• Excisional biopsy or resection: Craniotomy for the surgical resection of focal, well-circumscribed lesions may provide not only a tissue diagnosis but also a prolonged event-free survival in some cases.
• Midbrain focal tumors approached in variety of ways: Rostral midbrain lesion can be resected via a subtemporal transtentorial approach (44). Other approaches used for midbrain lesions are frontotemporal transsylvian with orbitozygomatic craniotomy, transpetrosal, far subtemporal, or a combination of these approaches to enable the shortest trajectory to the tumor (45). Atypical lesions can be approached by supracerebellar-infratentorial or suboccipital-transtentorial routes. Surgery of ventral midbrain tumors may be associated with considerable morbidity (34, 44).  Resection or open biopsy of tectal tumors is rarely indicated. 
• Medulla and pontine focal tumors approached through fourth ventricle: Key in the strategy for approaching these tumors is preservation of cranial nerve function. One very effective tool for accomplishing this has been the introduction of cranial nerve mapping (98). It allows entry into the brainstem while preserving motor nerve function.

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.