Nervous system tumors are classified into primary central nervous system (CNS) tumors (intracranial and intraspinal tumors) and metastatic CNS tumors (brain metastases, the most common intracranial tumors, accounting for 20-40% of all intracranial neoplasms). Primary intracranial tumors are dominated by gliomas (40-50% of primary intracranial tumors, WHO grade I-IV, with grade IV glioblastoma [GBM] being the most malignant), meningiomas (20-30%, mostly benign), pituitary adenomas (10-15%, mostly benign), vestibular schwannomas (5-8%, benign), medulloblastomas (the most common malignant pediatric brain tumor), germ cell tumors, and craniopharyngiomas.

• Etiology: The etiology of most primary CNS tumors is unknown, with confirmed risk factors including ionizing radiation, hereditary tumor syndromes (neurofibromatosis, von Hippel-Lindau syndrome, Lynch syndrome), and immunodeficiency. Brain metastases most commonly originate from lung cancer, breast cancer, melanoma, and gastrointestinal malignancies.
• Clinical Manifestations: The most common presenting symptoms are increased intracranial pressure (headache, vomiting, papilledema), focal neurological deficits (limb weakness, sensory loss, aphasia, ataxia, visual/hearing loss), and seizures. Pituitary adenomas present with endocrine symptoms (amenorrhea, galactorrhea, acromegaly, Cushing syndrome). Pediatric brain tumors commonly present with hydrocephalus, gait instability, and developmental delay.
• Diagnosis: Contrast-enhanced cranial/spinal MRI is the gold standard for diagnosis and localization. CT is used to evaluate calcification and bony changes. PET-CT is used for systemic staging and detecting metastases. Histopathological confirmation via surgical or stereotactic biopsy is the gold standard for diagnosis and WHO grading. Mandatory molecular profiling includes IDH1/2 mutation, 1p/19q codeletion, MGMT promoter methylation, TERT promoter mutation, and H3 K27M mutation for gliomas, as well as endocrine hormone testing for pituitary adenomas.

• Gliomas: For low-grade gliomas (WHO I-II), maximal safe surgical resection is the standard, with adjuvant radiotherapy/chemotherapy for high-risk patients. For high-grade gliomas (WHO III-IV, anaplastic glioma, GBM), the standard of care is maximal safe surgical resection followed by concurrent chemoradiotherapy with temozolomide and adjuvant temozolomide (Stupp regimen). Recurrent disease is managed with repeat surgery, re-irradiation, chemotherapy, tumor treating fields (TTFields), targeted therapy, immunotherapy, and clinical trials.
• Meningiomas: For asymptomatic small WHO grade I meningiomas, active surveillance is standard. For symptomatic or growing tumors, gross total surgical resection (Simpson grade I) is curative, with a 10-year recurrence rate of <10%. Stereotactic radiosurgery (SRS, gamma knife) is indicated for residual/recurrent tumors, small tumors, or patients unfit for surgery. For atypical/anaplastic meningiomas (WHO II-III), surgical resection plus adjuvant radiotherapy is standard.
• Pituitary Adenomas: For prolactinomas, medical therapy with dopamine agonists (bromocriptine, cabergoline) is first-line. For all other functional adenomas and non-functional adenomas with mass effect, transsphenoidal endoscopic resection is the surgical gold standard, with adjuvant radiotherapy and medical therapy for residual/recurrent disease.
• Vestibular Schwannomas: Gross total surgical resection with facial and cochlear nerve preservation is the curative standard. SRS (gamma knife) is indicated for small tumors, residual/recurrent disease, or patients unfit for surgery.
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