Pediatric Brain Tumors

Increased Intracranial Pressure Mechanism

• Tumors occupy space within the fixed cranial vault, increasing ICP and reducing cerebral perfusion pressure
• Obstruction of cerebrospinal fluid (CSF) flow, particularly at the fourth ventricle (common with posterior fossa tumors), causes hydrocephalus and further ICP elevation
• Disruption of the blood-brain barrier increases vasogenic edema, amplifying mass effect
• Elevated ICP manifests as headache, vomiting, and papilledema; critical thresholds lead to altered consciousness and herniation

Focal Neurological Dysfunction

• Compression of white matter tracts disrupts motor, sensory, and coordination pathways
• Involvement of the cerebellum produces ataxia, dysmetria, and hypotonia
• Brainstem compression causes cranial nerve palsies, particularly affecting CN V-XII
• Infiltration of specific nuclei results in specific syndromes (e.g., Parinaud syndrome with pineal region tumors affecting vertical gaze)

Molecular Oncogenic Mechanisms

• Medulloblastomas arise from cerebellar granule neuron precursors; major subtypes include WNT-activated (wingless pathway), SHH-activated (sonic hedgehog—associated with TP53 mutations and very poor prognosis when TP53-mutant), Group 3, and Group 4
• Pilocytic astrocytomas typically harbor BRAF V600E mutations or BRAF-KIAA1549 fusions, activating MAPK signaling; generally low-grade with indolent behavior
• Diffuse midline gliomas (brainstem, thalamic) frequently carry H3K27M mutations (lysine-to-methionine substitution in histone H3), epigenetically silencing tumor suppressors and conferring aggressive behavior
• Loss of chromosome 1p and 19q in oligodendrogliomas is associated with chemotherapy sensitivity and improved prognosis

Endocrinological Disruption

• Sellar/suprasellar tumors (craniopharyngioma, optic pathway glioma) compress the pituitary stalk or gland itself
• Hypothalamic involvement disrupts gonadotropin-releasing hormone (GnRH), causing growth hormone deficiency, central hypothyroidism, and central hypogonadism
• Posterior pituitary dysfunction may develop, leading to diabetes insipidus from ADH deficiency

Genetic Predisposition Syndromes

• Neurofibromatosis Type 1 (NF1): Increased risk of optic pathway gliomas (25% of NF1 patients), brainstem gliomas, and malignant peripheral nerve sheath tumors; TP53 mutations elevate malignancy risk
• Li-Fraumeni Syndrome (TP53 mutations): Dramatically elevated risk of medulloblastoma and glioma; associated with early-onset, often multifocal or bilateral tumors
• Gorlin Syndrome (PTCH1 mutations): Predisposes to SHH-activated medulloblastoma; also associated with multiple skin cancers and odontogenic keratocysts
• Turcot Syndrome: APC mutations increase colorectal and CNS tumor risk, particularly medulloblastoma
• Cowden Syndrome (PTEN mutations): Elevated breast cancer risk; associated with dysplastic cerebellar gangliocytoma (Lhermitte-Duclos disease)

Non-Genetic Risk Factors

• Prior CNS radiation: Dose-dependent risk; notably increased for secondary malignancies (glioma, meningioma) following treatment of leukemia or other primary malignancies
• Immunodeficiency: Markedly increased lymphoma risk in HIV/AIDS and post-transplant settings; primary CNS lymphoma is AIDS-defining with CD4 <50
• Environmental exposures: Extremely limited evidence; no proven causal link to pesticides, electromagnetic fields, or cellular phone use in children

Spontaneous Genetic Events

• The majority of pediatric brain tumors are sporadic, arising from de novo mutations and chromosomal alterations accumulated during early neural development
• Age-related mutation burden increases throughout childhood, explaining the bimodal age distribution of certain tumor types

Cardinal Symptoms (in decreasing frequency)

• Morning headache and vomiting: Classically worse upon waking due to overnight ICP elevation in supine position; vomiting often occurs without nausea (projectile), reflecting direct medullary irritation
• Ataxia and gait disturbance: Hallmark of posterior fossa tumors; may be subtle (unsteady gait) or severe (inability to walk)
• Developmental delay or regression: Cognitive and motor regression in young children; may be attributed incorrectly to developmental disorders
• Head tilt or torticollis: Seen with posterior fossa masses, representing an attempt to relieve neck pain and ICP
• Visual disturbances: Diplopia (brainstem involvement), visual field defects (optic pathway compression), or nystagmus (cerebellar dysfunction)
• Behavior change, personality change, or school decline: Often attributed to psychological causes, particularly insidious in slower-growing tumors
• Seizures: More common with supratentorial tumors; may be the presenting symptom in cortical or superficial lesions
• Endocrine abnormalities: Growth failure, precocious or delayed puberty, polyuria/polydipsia (diabetes insipidus)

Physical Examination Findings

• Papilledema: Indicates chronic or acute elevated ICP; optic disc swelling, obscuration of margins, loss of spontaneous venous pulsations
• Cranial nerve palsies: CN VI palsy (abducens) from raised ICP causing downward brainstem displacement; CN III and IV involvement suggests direct midbrain/pons compression; CN VII, VIII involvement in cerebellopontine angle tumors (e.g., acoustic neuroma, though rare in young children)
• Cerebellar signs: DANISH mnemonic—Dysdiadochokinesia, Ataxia, Nystagmus, Intention tremor, Scanning speech, Hypotonia
• Hydrocephalus signs: Macrocephaly (in infants whose sutures remain open), separated sutures, sunset eyes (downward deviation from aqueductal stenosis), bulging fontanelle
• Parinaud syndrome: Impaired upward gaze, convergence-retraction nystagmus, light-near dissociation; pathognomonic for pineal/dorsal midbrain pathology
• Hemiparesis or hemisensory loss: Indicates hemispheric tumor with motor/sensory cortex or internal capsule involvement
• Spinal cord involvement: Leptomeningeal metastases cause lower extremity weakness, lower extremity hyperreflexia, Babinski sign

Neuroimaging—Gold Standard

• MRI brain and spine with and without gadolinium contrast: Superior soft-tissue resolution; T1 (fat-suppressed with contrast), T2, and FLAIR sequences; identifies tumor location, edema, hemorrhage, and cystic components; spinal MRI mandatory in all cases to exclude leptomeningeal or spinal cord metastases (found in 25-40% of medulloblastomas at presentation)
• Interpretation: T1-weighted shows tumor as iso- to hypointense; T2/FLAIR shows hyperintensity; enhancement with gadolinium indicates blood-brain barrier disruption
• CT head (non-contrast): Rapid assessment in acute setting; detects hemorrhage and bony erosion; less sensitive than MRI for soft tissue; useful for detecting calcification (common in ependymomas, craniopharyngiomas)
• MRI Advanced Techniques: Perfusion-weighted imaging (elevated cerebral blood volume in high-grade lesions), diffusion-weighted imaging (restricted diffusion in hypercellular tumors), MR spectroscopy (elevated choline/creatinine ratio; marker of malignancy)

Cerebrospinal Fluid (CSF) Analysis

• CSF cytology: Obtained via lumbar puncture or ventricular tap; detects leptomeningeal metastases; medulloblastomas and ependymomas have highest metastatic potential
• CSF tumor markers: Alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (β-hCG) in germ cell tumors; elevated levels indicate metastatic disease and carry poor prognostic significance
• Timing: CSF sampling delayed 10-14 days post-neurosurgery to avoid false-positive results from operative contamination

Tissue Diagnosis via Neurosurgery

• Stereotactic or open biopsy/resection: Definitive diagnosis; extent of resection is major prognostic factor (>90% resection associated with improved survival in many tumor types)
• Intraoperative neuromonitoring: Motor and sensory evoked potentials preserve function during tumor removal near eloquent cortex
• Frozen section: Rapid intraoperative pathologic assessment guides surgical strategy

Molecular and Genetic Testing

• Medulloblastoma subtyping: WNT (CTNNB1 mutations, excellent prognosis ~95% 5-year survival), SHH (PTCH1, SMO, SUFU mutations; worse if TP53-mutant), Group 3 and Group 4 (variable prognosis; Group 3 with MYC amplification particularly aggressive)
• Ependymoma subtyping: Supratentorial tumors with RELA/YAP1 fusions carry poor prognosis; infratentorial tumors with PFA and PFB subtypes have distinct biology
• Glioma grading: WHO 2021 classification; H3K27M presence indicates WHO Grade IV (regardless of histologic appearance); BRAF V600E and fusion status in pilocytic astrocytomas

Laboratory Studies

• Complete blood count (CBC): Baseline; some chemotherapy regimens cause myelosuppression requiring monitoring
• Comprehensive metabolic panel (CMP): Assess renal and hepatic function; baseline for chemotherapy monitoring
• Endocrine screening: Growth hormone, TSH, free T4, ACTH, cortisol, prolactin in sellar/suprasellar tumors; water deprivation test if diabetes insipidus suspected
• Ophthalmologic examination: Visual acuity, visual fields, fundoscopy to document papilledema and establish baseline for radiation effects

Diagnostic Criteria for Specific Tumors

• Medulloblastoma: Highly cellular, round blue cells; often with Homer-Wright rosettes; mitotic rate high; typically arise from cerebellar vermis
• Pilocytic astrocytoma: Biphasic pattern (compact and loose areas); Rosenthal fibers; eosinophilic granular bodies; low mitotic rate; typically WHO Grade I
• Brainstem glioma: MRI shows expansion of brainstem; biopsy often not performed (diagnosis radiologic); H3K27M testing essential for prognosis
• Ependymoma: Perivascular rosettes, ependymal rosettes, canals; ependymal differentiation diagnostic; tumor location (supratentorial vs. infratentorial) and molecular subtype critical for risk stratification

Multimodal Therapy Framework

First-Line Surgical Management

• Maximum safe resection (gross total resection if feasible): Goal is >90% resection for most tumor types; extent of resection is among the strongest independent prognostic factors
• Mechanism: Removes tumor burden, reduces mass effect, lowers ICP, improves chemotherapy drug delivery to remaining disease
• Technical considerations: Neuronavigation, intraoperative neuromonitoring, and awake craniotomy preserve eloquent cortex and white matter tracts
• Role of biopsy: When complete resection unsafe or tumor unresectable, stereotactic biopsy provides tissue diagnosis and guides further therapy
• Urgent decompression: For life-threatening ICP elevation, emergent external ventricular drain (EVD) placement if hydrocephalus present; allows ICP monitoring, CSF drainage, and CSF sampling

Chemotherapy by Tumor Type

• Standard high-dose multi-agent regimens: Induction with vincristine, cisplatin, cyclophosphamide, followed by high-dose chemotherapy with stem cell rescue
• Age-stratified approaches: Infants (<3 years) receive chemotherapy-only protocols to avoid radiation neurotoxicity; older children receive chemotherapy ± craniospinal irradiation (CSI) based on risk group
• Targeted therapy emerging: SHH inhibitors (vismodegib, sonidegib) for SHH-activated tumors; showing promise in trials, particularly for TP53-wildtype SHH tumors

• Observation for completely resected, nonprogressive tumors: Many are indolent; may never require chemotherapy
• Chemotherapy for progressive disease: Vincristine and carboplatin (VCB regimen) or alternative agents; response rates 40-60%
• BRAF-targeted therapy: Dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor) for BRAF V600E-mutant tumors showing dramatic responses; increasingly used as first-line for unresectable tumors

• Conventional chemotherapy: Limited efficacy; outcomes have not improved significantly with standard agents
• Radiation therapy: Focal external beam radiation (54-56 Gy) modestly improves progression-free survival
• Emerging targeted approaches: H3K27M inhibitors and other epigenetic therapies under investigation; currently available only in clinical trial settings

• Chemotherapy: Vincristine, cisplatin, etoposide (VCE) or similar regimens; role controversial, with no proven survival benefit in all subtypes
• Risk-adapted approach: Favorable tumors (GTR, supratentorial PFA) may receive observation; aggressive tumors (infratentorial, residual disease) receive chemoradiation

Radiation Therapy

• Conformal/intensity-modulated radiation therapy (IMRT): Delivers high-dose radiation to tumor while minimizing exposure to surrounding brain, especially in eloquent regions
• Craniospinal irradiation (CSI): 23-36 Gy whole brain and spine for high-risk medulloblastoma, ependymoma with metastases, and some pituitary tumors; addresses leptomeningeal disease
• Focal radiation: 54-56 Gy to tumor/surgical bed for localized disease without CNS metastases
• Age considerations: Radiation deferred in children <3 years when possible due to cognitive sequelae; chemotherapy intensified as substitute
• Proton beam therapy: Emerging modality with superior dose distribution, reducing late effects; increasingly used for pediatric tumors, though cost and availability limit access

Symptomatic Management and Supportive Care

• Corticosteroids (dexamethasone): Reduces cerebral edema; typical dose 0.5-1 mg/kg/day (max 4 mg/day) in divided doses; tapered slowly post-operatively to avoid adrenal insufficiency
• Anticonvulsants: Prophylaxis not routinely recommended; used therapeutically if seizures occur (**

Emergencies — recognize immediately

• Obstructive hydrocephalus with herniation: fourth-ventricular or aqueductal compression blocks CSF egress; the decompensating child shows depressed consciousness, Cushing triad (hypertension, bradycardia, irregular respirations), fixed dilated pupil (uncal), or neck stiffness with head tilt (tonsillar). Head elevation, hyperosmolar therapy, dexamethasone, and emergent CSF diversion (EVD or endoscopic third ventriculostomy) per neurosurgical/Neurocritical Care Society ICP principles.
• Lumbar puncture before imaging: withdrawing CSF below an obstructing posterior fossa mass creates a pressure gradient and precipitates tonsillar herniation — image first, always.
• Symptomatic leptomeningeal/"drop" metastasis: back pain, lower-extremity weakness, hyperreflexia, bowel/bladder dysfunction signal cord compression; urgent spine MRI and steroids.
• Adrenal crisis: abrupt steroid taper or tumor/surgical loss of ACTH produces hypotension, hypoglycemia, hyponatremia; stress-dose hydrocortisone precedes confirmatory testing (Endocrine Society hypopituitarism guidance).
• Febrile neutropenia during myelosuppressive chemotherapy: single fever plus neutropenia mandates cultures and immediate empiric antipseudomonal beta-lactam (IDSA/ASCO).

Postoperative complications

• Posterior fossa (cerebellar mutism) syndrome: dentato-thalamo-cortical tract injury after midline vermian resection; mutism, emotional lability, and ataxia appear 1–2 days after an initially awake patient — most common with medulloblastoma; largely recovers but often leaves dysarthria.
• CSF leak/pseudomeningocele and meningitis: clear rhinorrhea or a fluctuant wound with fever and meningismus.
• Sodium disorders: SIADH, cerebral salt wasting (hypovolemic), and central diabetes insipidus (dilute polyuria with hypernatremia) — hallmarks of suprasellar/craniopharyngioma surgery.

Late treatment effects (Children's Oncology Group Long-Term Follow-Up Guidelines)

• Neurocognitive decline: craniospinal irradiation injures white matter; worst in children under 3, driving chemotherapy-only infant protocols and proton therapy.
• Endocrinopathy: GH deficiency first, then TSH, ACTH, gonadotropins; growth failure and precocious puberty warrant auxology and pituitary testing.
• Second malignancy and vasculopathy: radiation-induced meningioma, high-grade glioma, and moyamoya (highest with NF1).
• Organ toxicity: cisplatin ototoxicity (high-frequency hearing loss on audiometry) and nephrotoxicity; vincristine neuropathy with areflexia/foot drop; cyclophosphamide hemorrhagic cystitis; hypothalamic obesity after craniopharyngioma.

• Posterior fossa is the default location: a school-age child with morning headache, vomiting without nausea, and ataxia has a posterior fossa mass until proven otherwise. Single best next step is MRI brain with and without gadolinium (plus total-spine MRI), never lumbar puncture first — LP below an obstructing mass can precipitate tonsillar herniation.
• Imaging pattern separates the big three: cystic cerebellar-hemisphere lesion with an enhancing mural nodule = pilocytic astrocytoma (Rosenthal fibers, BRAF fusion, WHO grade 1, best prognosis, resection may be curative); midline vermian mass filling the fourth ventricle with restricted diffusion and drop metastases = medulloblastoma (Homer-Wright rosettes, small round blue cells); "plastic" tumor squeezing out the foramina of Luschka/Magendie with calcification = ependymoma (perivascular pseudorosettes).
• Diffuse expansion of the pons with cranial neuropathies, long-tract signs, and ataxia = diffuse midline glioma, H3K27M-altered — WHO grade 4 regardless of histology; radiation is palliative and prognosis is dismal. Do not choose "gross total resection" as the answer.
• Suprasellar calcified cyst in a child with bitemporal hemianopsia and growth failure = craniopharyngioma from Rathke pouch remnants; aspirate yields "motor oil" fluid with cholesterol crystals. The distractor is pituitary adenoma, which is rare in children and typically non-calcified.
• Parinaud syndrome (upgaze palsy, convergence-retraction nystagmus, light-near dissociation) points to a pineal region tumor — send serum and CSF AFP and β-hCG for germ cell tumor before assuming a glioma.
• The association examiners love: NF1 → optic pathway pilocytic astrocytoma. Screen with serial ophthalmologic exams; these are typically followed or treated with chemotherapy/MEK inhibition rather than biopsied.
• CN VI palsy is a false localizing sign of raised ICP — do not localize the tumor to the pons because of it. In infants, papilledema may be absent; macrocephaly, split sutures, and sunsetting eyes replace it.
• New mutism 1–2 days after vermian tumor resection is posterior fossa syndrome, not stroke or psychiatric regression.