**2. Neuro-oncologic treatment modalities**

#### **2.1. Neurosurgery**

Neuro-oncology multidisciplinary team discussion allows for a non-bias, more appropriate decision, evident-based, and tailored according to local situation. The option between observation, surgical intervention, radiotherapy, chemotherapy, or a combination of these depends on many factors: tumor type, location, invasiveness as well as the patient's age and overall medical condition. Generally, if a tumor is accessible and the morbidity risk is acceptable, resection should be considered. Neurosurgeons should also actively follow up patients even if a nonsurgical approach is preferred since their interference might be re‐ quired for treating unsuccessful cases or complications of the chosen modality.

Thorough evaluation of the patient should be performed before a precise neurosurgical opinion including the clinical condition, neuroimaging studies, and case-specific pertinent investigations (e.g., serum hormone levels, tumor markers, genetic syndrome features, etc.). Imaging of the entire neuraxis should be performed, especially for tumors with a tendency for CNS dissemination such as medulloblastomas, germ cell tumors, ependymomas, and primitive neuroectodermal tumors (PNETs).

The main objectives of the neurosurgeons are as follows:


#### **2.2. Tumor resection**

Maximum safe resection can be performed for a lesion that significant neurological impair‐ ments can be avoided after its surgical removal. The patient's prognosis often correlates with the extent of resection.

#### **2.3. Histopathological diagnosis**

When pediatric CNS tumors are not amenable to surgical resection, a biopsy is required except in certain situation. Various biopsy techniques have been described and the choice of the appropriate method mainly depends on tumor location.

#### *A) Stereotactic biopsy*

Stereotactic coordinates are used for precise guidance of a needle inside the tumor. This is the method of choice for deeply located tumors. Stereotactic biopsy may be performed through a frameless via frameless neuro-navigation device or a metallic head frame-based system. The coordinates for adequate placement of the burr hole, the angulation, and depth of the needle are determined by preoperative images.
