*B) Open biopsy*

**2. Neuro-oncologic treatment modalities**

primitive neuroectodermal tumors (PNETs).

– Maximal safe tumor resection when possible

– Histopathological diagnosis

**2.2. Tumor resection**

the extent of resection.

*A) Stereotactic biopsy*

**2.3. Histopathological diagnosis**

The main objectives of the neurosurgeons are as follows:

– Treatment of associated conditions (e.g., hydrocephalus)

appropriate method mainly depends on tumor location.

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‐

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

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

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

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

quired for treating unsuccessful cases or complications of the chosen modality.

**2.1. Neurosurgery**

454 Neurooncology - Newer Developments

Open biopsy can be performed through a small craniotomy that allows for direct access to the tumor. This method is traditionally used for superficial tumors near or within the cerebral cortex or when leptomeningeal lesions are identified. Neuro-navigation can help in precise localization of the tumor in relation to the skull surface.

#### *C) Endoscopic endonasal biopsy*

Anterior skull base, sellar region, and tumors invading sinuses can sometimes be accessed through an endoscopic endonasal approach under general anesthesia.

## *D) Endoscopic intraventricular biopsy*

Tumors located adjacent to or within the ventricular system may be amenable to an endo‐ scopic transventricular approach. This procedure has the advantage of allowing treatment of associated hydrocephalus via endoscopic venticulostomy and obtaining intraventricular cerebrospinal fluid (CSF) sample.

## **2.4. Treatment of hydrocephalus**

Due to the mass effect of the tumor causing partial obstruction of the pathway of CSF, hydrocephalus may develop. The main mechanism of hydrocephalus in the context of CNS tumors is obstruction of the ventricular system by tumors in the posterior fossa and that located around the third ventricle [28].

Unstable patients with clinical evidence of elevated ICP should undergo urgent surgery, inserting external ventricular drain (EVD). The anterior horn of the lateral ventricle is accessed through an inserted catheter through a skull burr hole and CSF flow is ensured. The EVD is connected to an external collecting device and allows the excess CSF to be drained [29]. Endoscopic third ventriculostomy (ETV) is another option in hydrocephalus resulting from posterior fossa or pineal region tumors. An ETV creates a communication between the third ventricle and the interpeduncular cistern under endoscopic guidance within the ventricular system [29, 30]. Many patients need permanent diversion of CSF ventriculoperitoneal shunt (VPS). A proximal catheter is inserted inside the lateral ventricle and is then connected to a distal catheter tunneled subcutaneously till it reaches the peritoneum. A valve is commonly inserted between the proximal and the distal catheter and allows for one-way drainage control. One of the disadvantages of VPSs includes the theoretical risk of intraperitoneal seedling of neoplastic cells.

#### **2.5. Spinal cord neoplasms**

Intramedullary spinal cord tumors are rare in the pediatric population, representing around 4% of all CNS tumors. Complete surgical excision if feasible or debulking is the general approach for spinal cord tumors. This procedure often leads to favorable outcome besides providing sufficient materials for histological diagnosis.

#### **2.6. Management of cystic tumors**

Many pediatric CNS tumors are composed of a cystic component or having both cystic and solid parts. The potential space of the cystic portion creates an isolated microenvironment that may hinder local treatment (radiotherapy or local chemotherapy). Simple aspiration of the fluid that composes the cyst may sometimes be a sufficient treatment. Moreover, surgical resection can be considered for most cystic tumors. Local treatment may be applied includ‐ ing the insertion of a device in which medical therapy will be administered. Specifically, the use of intracystic radioisotope (radioactive iodine-125 or phosphorus 32) and intracavitary chemotherapy may be used in selected cases [31]. The main advantage of this treatment is the low rate of long-term sequelae. Intracystic chemotherapy has been advocated to delay aggressive treatment such as radical resection or irradiation. This method allows for admin‐ istration of effective therapy (commonly bleomycin or interferon) and abolishes the systemic toxicity of the systemic chemotherapy and the morbidity of surgical resection. Ommaya reservoir and instillations of single or multiple doses of active drugs remain the method of choice for intracystic chemotherapy.

#### **2.7. Management of tumor recurrence**

The decision to reoperate on a recurred tumor must be taken in the light of the patient's life expectancy and QoL, tumor histology, time length between initial resection and recurrence, the risks and benefits of a second surgery, and the potential for adjuvant therapy such as radiotherapy and chemotherapy. Each case should be individually evaluated through multidisciplinary discussion taking into consideration the patient's family opinion and preference. It is worth emphasizing that surgical treatment of recurrent tumors should be seriously considered as reoperation has improved survival for many tumors such as choroid plexus tumors, ependymomas, and cerebellar astrocytomas [32–34].
