Medical School · Year 3 · Neurology · includes a quiz and discussion video

Seminar 10: Neuro-oncology

Neurology Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Classify primary brain tumors according to WHO histological type, grade, and integrated molecular markers
2. Recognize the general and focal clinical presentations of both primary and metastatic CNS tumors
3. Differentiate primary brain tumors from metastatic disease using clinical features and neuroimaging characteristics
4. Apply a systematic diagnostic approach incorporating advanced neuroimaging, tissue biopsy, and molecular testing
5. Manage acute tumor-related complications including increased intracranial pressure, seizures, and venous thromboembolism
6. Identify paraneoplastic neurological syndromes and initiate appropriate cancer screening and immunotherapy

Seminar Outline

Section 1: Overview of Brain Tumors

Central nervous system tumors represent a diverse group of neoplasms with wide-ranging epidemiological, biological, and clinical characteristics. The incidence of primary CNS tumors is approximately 23 per 100,000 persons per year, but metastatic brain tumors are far more common, outnumbering primary brain tumors by a ratio of roughly 10 to 1. Glioblastoma stands as the most common malignant primary brain tumor, while meningioma is the most common primary brain tumor overall when both benign and malignant neoplasms are considered together. The distribution of tumor types differs substantially between pediatric and adult populations, with embryonal tumors such as medulloblastoma being far more prevalent in children, whereas glioblastoma and metastatic disease dominate in adults.

The classification of brain tumors draws upon both histological and molecular criteria. Glial tumors, which include glioblastoma, astrocytoma, and oligodendroglioma, arise from the supporting glial cells of the central nervous system and represent the most clinically significant category. Additional categories include neuronal tumors such as ganglioglioma and dysembryoplastic neuroepithelial tumor, meningeal tumors such as meningioma, embryonal tumors such as medulloblastoma, and sellar region tumors including pituitary adenoma and craniopharyngioma. Metastatic tumors, most frequently originating from lung, breast, and melanoma primaries, constitute a separate and extremely important category in the clinical management of brain neoplasms.

The World Health Organization 2021 grading system assigns grades 1 through 4 to CNS tumors based on their biological behavior. Grade 1 tumors demonstrate low proliferative potential and may be curable through surgical resection alone. Grade 2 tumors are considered low grade but exhibit infiltrative growth patterns that preclude complete surgical eradication. Grade 3 tumors possess anaplastic features including increased mitotic activity, and grade 4 tumors are highly malignant with hallmark findings of necrosis and microvascular proliferation. This grading system is fundamental to prognosis and treatment planning, as survival differs dramatically between grades.

Molecular classification has become an indispensable component of brain tumor diagnosis and has been formally integrated into the WHO 2021 classification system. The isocitrate dehydrogenase mutation is perhaps the most prognostically important molecular marker in gliomas, as IDH-mutant tumors carry a significantly better prognosis than their IDH-wildtype counterparts. The 1p/19q codeletion defines oligodendroglioma at the molecular level and predicts chemosensitivity. MGMT promoter methylation predicts a more favorable response to temozolomide chemotherapy. ATRX loss indicates astrocytic lineage, and the H3K27M mutation defines diffuse midline glioma, a devastating tumor primarily affecting children and young adults. Together, these markers have fundamentally transformed how neuro-oncologists classify and treat brain tumors.

<image>Panel A: Bar graph illustrating the epidemiology of primary versus metastatic brain tumors with incidence data and pie chart of tumor type distribution. Panel B: Hierarchical classification diagram showing major categories of brain tumors including glial, neuronal, meningeal, embryonal, sellar, and metastatic with representative examples for each. Panel C: Comparative histology images of WHO grades 1 through 4 showing progressive atypia, mitotic figures, microvascular proliferation, and necrosis. Panel D: Molecular pathway diagram illustrating key biomarkers including IDH mutation, 1p/19q codeletion, MGMT methylation, ATRX loss, and H3K27M mutation with their associated tumor types and prognostic implications.</image>

Section 2: Clinical Presentation

The clinical presentation of brain tumors is determined by a combination of generalized effects related to increased intracranial pressure and focal deficits attributable to the specific location of the lesion. Headache is among the most common presenting symptoms and is typically caused by elevated intracranial pressure, characteristically worsening in the morning and with Valsalva maneuvers such as coughing or straining. Seizures arise from cortical irritation and may be the first clinical manifestation of a brain tumor, particularly in patients with cortically located or low-grade lesions. Cognitive changes, nausea, vomiting, and papilledema are additional manifestations of increased intracranial pressure and mass effect, and their presence should always raise concern for an intracranial mass lesion.

Focal neurological symptoms depend on the anatomical location of the tumor. Frontal lobe tumors may produce personality changes, executive dysfunction, motor weakness, or abulia. Temporal lobe lesions can cause memory impairment, language difficulties when the dominant hemisphere is involved, and seizures. Parietal lobe tumors manifest as sensory loss or, when located in the non-dominant hemisphere, hemispatial neglect. Occipital lobe involvement results in visual field deficits such as homonymous hemianopia. Posterior fossa tumors present differently, with cerebellar lesions causing ataxia, dysarthria, and nystagmus, while brainstem tumors produce cranial nerve palsies and long tract signs including contralateral weakness or sensory changes.

Certain tumor types have classic clinical presentations that aid in diagnosis. Pituitary adenomas often present with bitemporal hemianopia from chiasmal compression and may be accompanied by hormonal dysfunction. Acoustic neuromas typically cause unilateral sensorineural hearing loss and tinnitus. Meningiomas tend to produce slowly progressive focal neurological deficits that evolve over months to years. Glioblastoma presents with rapidly progressive symptoms and characteristically appears as a ring-enhancing mass on imaging. Medulloblastoma is a pediatric tumor that typically arises in the cerebellum and presents with hydrocephalus due to obstruction of the fourth ventricle.

Several red flag features should prompt urgent evaluation for an intracranial mass lesion. A progressive neurological deficit that worsens over days to weeks raises suspicion for a growing mass lesion. New-onset seizures in an adult, particularly in someone over the age of 40 with no prior history of epilepsy, mandate structural neuroimaging to exclude a tumor or other structural cause. Headache accompanied by papilledema indicates dangerously elevated intracranial pressure and requires emergent investigation. Personality or behavioral changes, especially when progressive and unexplained by psychiatric history, should raise concern for a frontal lobe tumor. Recognizing these red flags enables timely diagnosis and intervention.

<image>Panel A: Diagram of the human brain with labeled regions showing symptom manifestations associated with tumors at each location including frontal, temporal, parietal, occipital, cerebellar, and brainstem sites. Panel B: Clinical photographs and MRI images illustrating classic presentations of pituitary adenoma with bitemporal hemianopia visual field chart, acoustic neuroma with audiogram, and glioblastoma with ring-enhancing MRI. Panel C: Fundoscopic photograph demonstrating papilledema with blurred disc margins, peripapillary hemorrhages, and venous engorgement as seen in elevated intracranial pressure. Panel D: Flowchart depicting red flag symptoms and the recommended evaluation pathway from clinical suspicion through urgent neuroimaging to subspecialty referral.</image>

Section 3: Diagnostic Approach

Neuroimaging forms the cornerstone of brain tumor diagnosis, with magnetic resonance imaging with gadolinium contrast serving as the primary modality for characterizing intracranial lesions. MRI provides superior soft tissue resolution and allows detailed assessment of tumor size, location, relationship to eloquent cortex, presence of edema, and enhancement pattern. Computed tomography is often the initial study obtained in the emergency setting, particularly when stroke or hemorrhage must be excluded, and is also useful for detecting calcification within tumors. Advanced imaging techniques such as MR spectroscopy, which evaluates the choline-to-N-acetylaspartate ratio, and perfusion MRI, which assesses cerebral blood volume, provide additional information that helps differentiate tumor types and grades. Positron emission tomography using fluorodeoxyglucose or amino acid tracers is particularly valuable for distinguishing tumor recurrence from radiation necrosis, a common and clinically challenging diagnostic dilemma.

MRI characteristics of brain tumors follow recognizable patterns that guide the differential diagnosis. Ring enhancement, in which the lesion periphery enhances brightly while the center remains hypointense due to necrosis, is characteristic of glioblastoma, metastatic disease, and brain abscess. Homogeneous enhancement is seen in meningiomas and primary CNS lymphoma. Low-grade gliomas typically do not enhance with contrast or show only patchy enhancement. Dural-based lesions with a characteristic dural tail sign are highly suggestive of meningioma. Multiple enhancing lesions at the gray-white matter junction strongly suggest metastatic disease. Restricted diffusion on diffusion-weighted imaging favors primary CNS lymphoma or abscess over other etiologies.

Tissue diagnosis remains essential for definitive classification and treatment planning. Stereotactic biopsy is employed when surgical resection is not feasible due to tumor location or patient factors, while open surgical resection is preferred when it can be performed safely, as it provides both diagnostic tissue and cytoreductive benefit. Molecular testing of tumor tissue for markers such as IDH mutation status, 1p/19q codeletion, and MGMT promoter methylation is now considered standard of care and is critical for both classification and treatment selection. Histopathological examination provides the WHO classification and grade, which, together with molecular data, constitute the integrated diagnosis that guides management.

The staging workup depends on the suspected tumor type. For patients with presumed metastatic disease, systemic staging with CT of the chest, abdomen, and pelvis, along with PET scanning, is performed to identify the primary malignancy and assess the extent of disease. For primary brain tumors with a propensity for cerebrospinal fluid dissemination, such as medulloblastoma, staging includes MRI of the entire spine and cerebrospinal fluid cytology. Primary CNS lymphoma requires a particular workup including slit-lamp ophthalmologic examination to evaluate for intraocular involvement, lumbar puncture for CSF analysis, and HIV testing given the known association between immunosuppression and CNS lymphoma. Comprehensive staging is essential for determining the appropriate treatment strategy and prognosis.

<image>Panel A: Side-by-side comparison of brain MRI sequences including T1-weighted, T1 with gadolinium contrast, T2-weighted, FLAIR, and diffusion-weighted imaging of a glioblastoma showing their complementary roles in characterization. Panel B: Gallery of MRI images demonstrating characteristic enhancement patterns of common brain tumors including ring-enhancing glioblastoma, dural-based meningioma with dural tail, periventricular lymphoma, and multiple gray-white junction metastases. Panel C: Illustration of stereotactic biopsy procedure with frameless neuronavigation system targeting a deep-seated lesion alongside photomicrographs of histological and molecular diagnostic studies. Panel D: Staging algorithm flowchart for suspected metastatic disease versus primary brain tumor versus primary CNS lymphoma showing appropriate workup for each pathway.</image>

Section 4: Primary Brain Tumors - Gliomas

Glioblastoma, classified as a grade 4 astrocytic tumor, is the most common and most aggressive malignant primary brain tumor. It predominantly affects older adults with a median age at diagnosis of approximately 65 years. On imaging, glioblastoma characteristically appears as a large, ring-enhancing mass with central necrosis surrounded by extensive vasogenic edema. Molecularly, glioblastoma is defined as IDH-wildtype and frequently harbors EGFR amplification, TERT promoter mutation, and gain of chromosome 7 with loss of chromosome 10. Despite aggressive multimodal therapy, the median survival remains approximately 15 months, underscoring the profound unmet need for more effective treatments.

Lower-grade gliomas encompass IDH-mutant astrocytomas and oligodendrogliomas, which carry substantially better prognoses than glioblastoma. IDH-mutant astrocytomas are graded from 2 to 4 and demonstrate ATRX loss, distinguishing them molecularly from oligodendrogliomas. Oligodendrogliomas are defined by the presence of both IDH mutation and 1p/19q codeletion and are notable for their chemosensitivity, particularly to the PCV regimen. On imaging, lower-grade gliomas are typically non-enhancing or show only patchy enhancement, helping to distinguish them from higher-grade tumors. Survival for lower-grade gliomas ranges from years to decades depending on grade, molecular features, and extent of resection.

Treatment of gliomas follows a multimodal approach that integrates surgery, radiation therapy, and chemotherapy. Maximal safe resection is a fundamental surgical principle, as greater extent of resection is consistently associated with improved survival across all glioma grades. Radiation therapy is standard for high-grade gliomas and is increasingly considered for low-grade gliomas with high-risk features. Temozolomide is the chemotherapeutic backbone for glioblastoma, administered concurrently with and after radiation in the Stupp protocol. The PCV regimen, consisting of procarbazine, lomustine, and vincristine, is particularly effective in oligodendrogliomas. Tumor-treating fields, which deliver alternating electric fields via scalp transducers, represent a newer treatment modality approved for glioblastoma that modestly improves survival when added to standard therapy.

Pediatric gliomas differ substantially from their adult counterparts in both biology and prognosis. Pilocytic astrocytoma, classified as WHO grade 1, is the most common pediatric brain tumor and typically arises in the cerebellum, where it is often amenable to surgical cure. In contrast, diffuse midline glioma harboring the H3K27M mutation is a devastating pediatric tumor affecting midline structures such as the pons, thalamus, and spinal cord, and carries a dismal prognosis with median survival of less than one year. Optic pathway gliomas are associated with neurofibromatosis type 1 and may require treatment with chemotherapy or targeted therapy rather than surgery given their location. Understanding the molecular underpinnings of pediatric gliomas has opened new avenues for targeted therapies, including BRAF inhibitors for tumors harboring BRAF alterations.

<image>Panel A: Axial T1 post-contrast MRI of glioblastoma demonstrating ring enhancement, central necrosis, and surrounding edema with annotated molecular features including IDH-wildtype status and EGFR amplification. Panel B: Comparative MRI and molecular profiles of IDH-mutant astrocytoma versus oligodendroglioma with 1p/19q codeletion showing differences in imaging appearance, molecular markers, and survival curves. Panel C: Schematic diagram of the Stupp protocol for glioblastoma treatment showing the sequence of maximal safe resection followed by concurrent radiation and temozolomide followed by adjuvant temozolomide cycles and tumor-treating fields. Panel D: MRI gallery of pediatric gliomas including a cerebellar pilocytic astrocytoma with cyst and enhancing mural nodule, a pontine diffuse midline glioma, and an optic pathway glioma with associated NF1 features.</image>

Section 5: Other Primary Brain Tumors

Meningiomas are the most common primary CNS tumors and arise from the arachnoid cap cells of the meninges. They are graded from 1 to 3, with grade 1 meningiomas being benign and accounting for the vast majority of cases. On imaging, meningiomas present as dural-based, homogeneously enhancing masses with a characteristic dural tail sign. Treatment consists of surgical resection, with radiation therapy reserved for residual or recurrent disease, particularly in grade 2 and 3 tumors. The prognosis for grade 1 meningiomas is excellent, with many patients achieving long-term disease control or cure through surgery alone, whereas higher-grade meningiomas carry increased risk of recurrence and require closer surveillance.

Primary CNS lymphoma is a rare but important brain tumor, typically manifesting as diffuse large B-cell lymphoma confined to the central nervous system. It is strongly associated with immunocompromised states including HIV infection and organ transplantation, although it also occurs in immunocompetent patients. On imaging, primary CNS lymphoma characteristically appears as a periventricular, homogeneously enhancing mass, and may be multifocal. The diagnostic workup includes slit-lamp examination to assess for intraocular involvement, lumbar puncture for CSF cytology and flow cytometry, and HIV testing. A critical management principle is to avoid corticosteroids prior to biopsy, as steroids can cause rapid tumor regression and obscure the histological diagnosis. Treatment centers on high-dose methotrexate-based chemotherapy combined with rituximab, and whole-brain radiation therapy is avoided in first-line treatment due to its significant neurocognitive toxicity.

Vestibular schwannoma, also known as acoustic neuroma, is a benign tumor arising from the Schwann cells of the vestibular portion of cranial nerve VIII. Patients typically present with progressive unilateral sensorineural hearing loss, tinnitus, and imbalance. On imaging, the tumor appears as an enhancing mass in the cerebellopontine angle. Treatment options include observation with serial imaging for small or minimally symptomatic tumors, surgical resection, and stereotactic radiosurgery. Bilateral vestibular schwannomas are pathognomonic for neurofibromatosis type 2 and should prompt genetic testing and screening for other associated tumors including meningiomas and ependymomas.

Pituitary tumors encompass a spectrum of lesions arising in the sellar region. Pituitary adenomas are the most common sellar tumors and are classified as functioning or non-functioning based on hormone secretion. Functioning adenomas include prolactinomas, growth hormone-secreting tumors causing acromegaly, and ACTH-secreting tumors causing Cushing disease. Non-functioning adenomas present with mass effect, including visual field deficits from optic chiasm compression and hypopituitarism. Treatment of prolactinomas is primarily medical, using dopamine agonists such as cabergoline, while other adenomas are typically managed with transsphenoidal surgery. Craniopharyngiomas are additional sellar-region tumors that are often suprasellar, characteristically calcified, and managed with surgery and radiation therapy.

<image>Panel A: Sagittal and axial MRI of a convexity meningioma demonstrating dural-based morphology with homogeneous enhancement and dural tail sign, alongside a table of WHO grade 1 through 3 features. Panel B: Axial MRI of periventricular primary CNS lymphoma with homogeneous enhancement, accompanied by a diagnostic workup algorithm including slit-lamp examination, lumbar puncture, and HIV testing. Panel C: Axial MRI of a cerebellopontine angle vestibular schwannoma with annotated audiogram showing unilateral high-frequency sensorineural hearing loss. Panel D: Coronal MRI of a pituitary macroadenoma with suprasellar extension compressing the optic chiasm, with insets showing visual field testing demonstrating bitemporal hemianopia and hormonal evaluation results.</image>

Section 6: Metastatic Brain Tumors

Metastatic brain tumors are the most common intracranial neoplasms encountered in clinical practice, reflecting the high prevalence of systemic cancers with a propensity for central nervous system dissemination. The most frequent primary sources are lung cancer, which accounts for the largest proportion of brain metastases, followed by breast cancer, melanoma, renal cell carcinoma, and colorectal cancer. Brain metastases preferentially lodge at the gray-white matter junction, where the narrowing caliber of penetrating blood vessels traps tumor emboli, and are also commonly found in the cerebellum and watershed areas. Approximately 50 to 70 percent of patients with brain metastases present with multiple lesions, while a minority present with a solitary metastasis, and roughly 10 percent of patients present with brain metastases as the first manifestation of an unknown primary cancer.

The clinical presentation of metastatic brain tumors is similar to that of primary brain tumors and includes headache with or without features of increased intracranial pressure, focal neurological deficits determined by lesion location, seizures, and cognitive dysfunction. The tempo of symptom progression varies but is generally subacute, evolving over days to weeks. A careful systemic review of symptoms and a thorough physical examination may provide clues to the primary malignancy, but in a significant minority of cases, the primary tumor remains occult at the time of brain metastasis diagnosis.

Imaging characteristics of brain metastases follow several recognizable patterns. Multiple enhancing lesions at the gray-white matter junction are the classic finding and strongly suggest metastatic disease. Ring enhancement is common, and surrounding vasogenic edema is often disproportionately large relative to the size of the enhancing lesion itself. Certain primary tumors have a predilection for hemorrhagic metastases, including melanoma, renal cell carcinoma, thyroid carcinoma, and choriocarcinoma. The finding of a solitary enhancing lesion poses a broader differential diagnosis that includes primary brain tumor, abscess, and demyelinating disease, and may require tissue diagnosis for definitive characterization.

Treatment of brain metastases is guided by the number and size of lesions, the patient's overall prognosis and systemic disease status, and the molecular characteristics of the primary tumor. Surgical resection is appropriate for a single accessible, symptomatic lesion, particularly when the diagnosis is uncertain or the mass effect is life-threatening. Stereotactic radiosurgery delivers highly focused radiation and is effective for a limited number of lesions, typically one to four, each measuring less than three to four centimeters in maximum diameter. Whole-brain radiation therapy is reserved for patients with numerous metastases or a poor overall prognosis. Systemic therapies, including targeted agents and immune checkpoint inhibitors, have shown increasing efficacy for brain metastases from certain primary tumors, particularly melanoma and non-small cell lung cancer with actionable mutations. Supportive measures including corticosteroids for edema and antiepileptic drugs for seizures are integral to comprehensive management.

<image>Panel A: Diagram of the human body illustrating the most common primary cancer sites that metastasize to the brain with relative frequency data for lung, breast, melanoma, renal, and colon. Panel B: Axial MRI showing multiple ring-enhancing lesions at the gray-white junction with surrounding edema characteristic of metastatic disease. Panel C: Comparison of hemorrhagic brain metastases on CT and MRI from melanoma and renal cell carcinoma with typical imaging signatures. Panel D: Treatment algorithm for brain metastases showing decision pathways based on number of lesions, size, systemic disease status, and molecular features leading to surgical resection, stereotactic radiosurgery, whole-brain radiation, or systemic therapy.</image>

Section 7: Complications of CNS Tumors

Increased intracranial pressure is one of the most dangerous complications of CNS tumors and can lead to brain herniation and death if not promptly recognized and treated. Initial management includes elevating the head of the bed to 30 degrees to facilitate venous drainage and administering high-dose dexamethasone, typically given as a 10 milligram intravenous loading dose followed by 4 milligrams every 6 hours, which reduces peritumoral vasogenic edema. For acute deterioration with signs of herniation, osmotic therapy with intravenous mannitol provides rapid but temporary reduction in intracranial pressure. Hyperventilation can serve as a brief temporizing measure by inducing cerebral vasoconstriction, but its effect is transient and should not be relied upon as a definitive treatment. Surgical decompression, either through tumor resection or placement of a ventricular drain, is indicated when medical measures are insufficient.

Tumor-related seizures affect 20 to 80 percent of brain tumor patients, with the incidence varying significantly by tumor type and location. Low-grade gliomas and cortically situated tumors carry the highest seizure risk, while deep-seated or posterior fossa tumors are less frequently associated with epilepsy. Prophylactic antiepileptic drugs are not routinely recommended for brain tumor patients who have not had a seizure, as clinical trials have not demonstrated benefit. When treatment is required, non-enzyme-inducing antiepileptic drugs such as levetiracetam and lacosamide are preferred because enzyme-inducing agents like phenytoin and carbamazepine interact with chemotherapeutic agents and corticosteroids, potentially reducing their efficacy and complicating drug management.

Venous thromboembolism represents a major source of morbidity and mortality in brain tumor patients, with glioblastoma carrying a particularly high risk estimated at 20 to 30 percent over the disease course. Prophylaxis includes mechanical measures such as compression stockings and intermittent pneumatic compression devices, along with pharmacological prophylaxis with low-molecular-weight heparin initiated in the postoperative period. When venous thromboembolism occurs, therapeutic anticoagulation is indicated even in the presence of a brain tumor, as the risk of fatal pulmonary embolism generally outweighs the risk of intracranial hemorrhage in most patients. The choice of anticoagulant, whether low-molecular-weight heparin or a direct oral anticoagulant, is made on a case-by-case basis considering bleeding risk, tumor characteristics, and patient preferences.

Cognitive effects are a pervasive complication of brain tumors and their treatments. The tumor itself causes cognitive impairment through direct infiltration, mass effect, and disruption of neural networks. Radiation therapy, while essential for tumor control, is associated with delayed cognitive decline that may manifest months to years after treatment, particularly following whole-brain radiation. Corticosteroids, despite their therapeutic benefits for edema, can adversely affect cognition, sleep, and mood. Management of cognitive dysfunction involves a multidisciplinary approach including cognitive rehabilitation programs, pharmacological interventions such as psychostimulants like methylphenidate, and optimization of modifiable factors such as sleep, mood, and medication side effects.

<image>Panel A: Step-by-step emergency management protocol for increased intracranial pressure showing head elevation, dexamethasone dosing, mannitol administration, hyperventilation parameters, and surgical intervention criteria. Panel B: Graph showing seizure incidence by tumor type and location with an inset table comparing enzyme-inducing versus non-enzyme-inducing antiepileptic drugs and their interactions with chemotherapeutic agents. Panel C: Venous thromboembolism risk stratification diagram for brain tumor patients with prophylaxis and treatment algorithms including mechanical, pharmacological, and anticoagulation options. Panel D: Timeline illustration showing the sources and progression of cognitive effects from diagnosis through treatment including tumor-related, surgery-related, radiation-related, and medication-related cognitive impacts with corresponding intervention strategies.</image>

Section 8: Radiation and Its Effects

Radiation therapy is a cornerstone of brain tumor treatment and encompasses several distinct techniques tailored to specific clinical situations. Conventional fractionated radiation therapy, delivered in small daily doses over several weeks, is the standard approach for gliomas and allows the surrounding normal brain tissue to repair sublethal damage between fractions. Stereotactic radiosurgery delivers a high dose of precisely focused radiation in a single session and is particularly effective for brain metastases and small, well-defined tumors. Proton beam therapy offers a dosimetric advantage by depositing the majority of its energy at a defined depth, reducing radiation exposure to surrounding normal tissue, and is particularly valuable in pediatric patients where minimizing late effects is paramount. Whole-brain radiation therapy treats the entire cranial contents and is reserved primarily for patients with multiple brain metastases, though its use has declined due to its significant neurocognitive toxicity.

Acute effects of radiation therapy develop during or shortly after the treatment course and are generally self-limited. Fatigue is the most common acute side effect and may persist for weeks after completion of treatment. Scalp erythema and alopecia within the radiation field are common dermatological effects. Acute neurological worsening may occur during or immediately after radiation due to increased peritumoral edema, which is typically managed with a temporary increase in corticosteroid dosing. These acute effects, while distressing to patients, are generally reversible and should not preclude completion of the radiation course.

Late effects of radiation therapy are of greater clinical concern due to their progressive and often irreversible nature. Radiation necrosis, a focal area of tissue death within the previously irradiated volume, can develop months to years after treatment and may be clinically and radiographically indistinguishable from tumor recurrence. Delayed cognitive decline is a well-documented consequence of cranial radiation, particularly whole-brain radiation, and is attributed to damage to neural progenitor cells in the hippocampus and disruption of white matter integrity. Secondary malignancies, including meningiomas and gliomas, may develop within the irradiated field years to decades after treatment. Endocrinopathy occurs when the pituitary gland or hypothalamus falls within the radiation field, necessitating long-term hormonal monitoring and replacement.

Distinguishing radiation necrosis from tumor recurrence is one of the most challenging problems in neuro-oncology, as both entities can present with new or worsening neurological symptoms and ring-enhancing lesions on conventional MRI. Radiation necrosis typically develops between 3 months and 3 years after treatment, while recurrence can occur at any time. Advanced imaging techniques are essential for differentiation. Perfusion MRI shows decreased cerebral blood volume in radiation necrosis but increased perfusion in recurrent tumor. PET imaging demonstrates decreased metabolic activity in necrotic tissue and increased uptake in viable tumor. When imaging is inconclusive, surgical biopsy may be necessary. Treatment of radiation necrosis includes corticosteroids, bevacizumab, which targets the vascular endothelial growth factor pathway involved in necrosis pathophysiology, and surgical resection for refractory cases.

<image>Panel A: Comparative illustration of radiation therapy techniques showing conventional fractionated radiation, stereotactic radiosurgery with dose falloff curves, proton beam therapy with Bragg peak, and whole-brain radiation with dose distribution maps. Panel B: Timeline showing acute radiation effects including fatigue, alopecia, and edema with their onset and resolution during and after a typical six-week treatment course. Panel C: Schematic showing late radiation effects arranged on a timeline from months to decades including radiation necrosis, cognitive decline, secondary malignancy, and endocrinopathy with risk factors for each. Panel D: Side-by-side comparison of radiation necrosis versus tumor recurrence on conventional MRI, perfusion MRI, and PET imaging with annotated distinguishing features and a management decision tree.</image>

Section 9: Paraneoplastic Neurological Syndromes

Paraneoplastic neurological syndromes are a group of disorders in which neurological dysfunction arises as a remote effect of a systemic cancer, mediated not by direct tumor invasion or metastasis but by an immune response directed against neural antigens shared between the tumor and the nervous system. These syndromes are important to recognize because neurological symptoms may precede the diagnosis of the underlying cancer by months to years, and identification of a paraneoplastic syndrome should prompt a thorough search for an occult malignancy. The antibodies produced against onconeural antigens serve as both diagnostic markers and clues to the most likely underlying tumor type. Early recognition and treatment of both the neurological syndrome and the underlying cancer are critical for achieving the best possible outcomes.

Several classic paraneoplastic syndromes are well characterized in terms of their clinical features, associated antibodies, and underlying malignancies. Limbic encephalitis presents with subacute memory loss, psychiatric symptoms, and seizures and is associated with anti-Hu antibodies in the setting of small cell lung cancer or with anti-NMDA receptor antibodies in association with ovarian teratoma. Paraneoplastic cerebellar degeneration causes rapidly progressive pancerebellar dysfunction including ataxia, dysarthria, and nystagmus and is most commonly associated with anti-Yo antibodies and ovarian or breast cancer. Paraneoplastic sensory neuropathy, characterized by painful asymmetric sensory loss, is associated with anti-Hu antibodies and small cell lung cancer. Lambert-Eaton myasthenic syndrome, which causes proximal weakness and autonomic dysfunction, is caused by anti-voltage-gated calcium channel antibodies and is strongly associated with small cell lung cancer. Opsoclonus-myoclonus syndrome, featuring involuntary chaotic eye movements and myoclonic jerks, is associated with anti-Ri antibodies and occurs with breast cancer, small cell lung cancer, and neuroblastoma in children.

Anti-NMDA receptor encephalitis deserves special attention due to its increasing recognition and unique clinical profile. It predominantly affects young women and is strongly associated with ovarian teratoma, although it can also occur without an identifiable tumor. The clinical presentation follows a characteristic progression beginning with psychiatric symptoms and progressing through seizures, movement disorders including orofacial dyskinesias, autonomic instability, and decreased level of consciousness. Diagnosis is confirmed by the detection of anti-NMDA receptor antibodies in both serum and cerebrospinal fluid. Treatment involves removal of the associated teratoma when present, followed by first-line immunotherapy with corticosteroids, intravenous immunoglobulin, or plasma exchange, and second-line agents including rituximab and cyclophosphamide for refractory cases.

The evaluation of suspected paraneoplastic syndromes requires a systematic approach. Antibody testing of both serum and cerebrospinal fluid for a comprehensive panel of onconeural antibodies is the initial diagnostic step. Cancer screening should be guided by the antibody profile and includes CT of the chest, abdomen, and pelvis, whole-body PET scanning, mammography, and pelvic ultrasound. If initial screening is negative, repeat evaluation should be performed at 6-month intervals for at least 2 years given the possibility that the tumor may be occult at initial presentation. Treatment of the underlying cancer is the most important therapeutic intervention, as tumor removal eliminates the antigenic stimulus driving the immune response. Immunotherapy with intravenous immunoglobulin, corticosteroids, plasmapheresis, and rituximab is employed to modulate the aberrant immune response. Prognosis is variable and depends on the specific syndrome, the antibody type, whether a tumor is identified and treated, and the timeliness of immunotherapy initiation.

<image>Panel A: Conceptual diagram illustrating the pathophysiology of paraneoplastic syndromes showing tumor expression of neural antigens, immune system activation, antibody production, and cross-reactivity with nervous system targets. Panel B: Summary chart of classic paraneoplastic syndromes depicting the clinical presentation, associated antibody, and underlying cancer for limbic encephalitis, cerebellar degeneration, sensory neuropathy, Lambert-Eaton syndrome, and opsoclonus-myoclonus. Panel C: Clinical progression timeline of anti-NMDA receptor encephalitis showing the sequential development of psychiatric symptoms, seizures, movement disorders, autonomic instability, and decreased consciousness with corresponding EEG and MRI findings. Panel D: Diagnostic and treatment algorithm for suspected paraneoplastic syndrome including antibody testing, cancer screening protocol with imaging modalities, immunotherapy options, and follow-up surveillance schedule.</image>

Section 10: Supportive Care and Prognosis

Symptomatic management is a critical component of care for patients with CNS tumors and addresses the diverse array of symptoms that can profoundly impact quality of life. Dexamethasone remains the primary agent for managing peritumoral edema and is titrated to the minimum effective dose to minimize side effects including hyperglycemia, myopathy, insomnia, and immunosuppression. Non-enzyme-inducing antiepileptic drugs are used for seizure control, with levetiracetam being the most commonly prescribed agent due to its favorable drug interaction profile and ease of use. Pain management follows a multimodal approach incorporating analgesics appropriate to the pain type and severity. Fatigue, one of the most prevalent and debilitating symptoms, may respond to psychostimulants such as methylphenidate. Depression is common in brain tumor patients and should be treated with antidepressants, as untreated mood disorders significantly worsen quality of life and functional outcomes.

Quality of life considerations span multiple domains and require a comprehensive multidisciplinary approach. Physical and occupational therapy are essential for maintaining and recovering functional independence, particularly after surgery or during periods of neurological decline. Speech and language therapy addresses communication difficulties, dysphagia, and cognitive-linguistic deficits. Cognitive rehabilitation programs employ compensatory strategies and restorative techniques to help patients manage the cognitive effects of the tumor and its treatment. Psychological and psychiatric support, including individual counseling, psychotherapy, and support groups, addresses the emotional and existential challenges faced by patients and their families. Social work services help navigate practical concerns including insurance, disability, transportation, and caregiver support.

Prognosis varies enormously across different brain tumor types and reflects the fundamental biological heterogeneity of CNS neoplasms. Glioblastoma carries the poorest prognosis among primary brain tumors, with a median survival of approximately 15 to 18 months despite maximal multimodal therapy. Anaplastic astrocytoma, classified as grade 3, has a median survival of 2 to 3 years. Low-grade gliomas afford substantially longer survival, ranging from 5 to 15 years depending on molecular features and extent of resection. Grade 1 meningiomas carry a near-normal life expectancy when completely resected. The prognosis for brain metastases is highly variable and depends primarily on the status of the systemic disease, the number and size of brain lesions, and the availability of effective systemic therapies.

End-of-life care is an integral component of neuro-oncologic management, particularly for patients with high-grade gliomas and progressive metastatic disease. Goals-of-care discussions should be initiated early in the disease course and revisited regularly as the clinical situation evolves, rather than being deferred to the final stages of illness. Advance directives, including designation of a healthcare proxy and documentation of preferences regarding resuscitation and life-sustaining treatments, should be completed while the patient retains decision-making capacity. Hospice referral is appropriate when disease-directed therapy is no longer effective or desired and should be presented as an affirmative choice for comfort-focused care rather than an abandonment of treatment. Symptom management at the end of life focuses on comfort and dignity, addressing pain, agitation, seizures, respiratory distress, and emotional and spiritual needs of both the patient and their loved ones.

<image>Panel A: Infographic displaying the pharmacological management of common brain tumor symptoms including edema, seizures, pain, fatigue, and depression with first-line agents and dosing considerations. Panel B: Multidisciplinary care wheel showing the roles of physical therapy, occupational therapy, speech therapy, cognitive rehabilitation, psychology, social work, and palliative care in comprehensive brain tumor management. Panel C: Survival curve comparison across brain tumor types including glioblastoma, anaplastic astrocytoma, low-grade glioma, meningioma, and brain metastases illustrating the wide range of prognoses. Panel D: End-of-life care framework showing the timeline of goals-of-care discussions, advance directive completion, hospice referral criteria, and symptom management priorities during the terminal phase.</image>

Summary

• Metastatic brain tumors are more common than primary tumors by a ratio of 10 to 1, with lung, breast, and melanoma being the most frequent primary sources
• Glioblastoma is the most common malignant primary brain tumor, presenting as a ring-enhancing mass with a median survival of approximately 15 months
• IDH mutation status is the single most important molecular marker in gliomas, conferring a significantly better prognosis when present
• The 1p/19q codeletion molecularly defines oligodendroglioma and predicts chemosensitivity to the PCV regimen
• Meningioma is the most common primary CNS tumor overall and characteristically appears as a dural-based, homogeneously enhancing mass
• Primary CNS lymphoma appears periventricular on imaging, and corticosteroids must be avoided before biopsy to prevent obscuring the diagnosis
• Treatment of high-grade gliomas involves maximal safe resection followed by concurrent radiation and temozolomide chemotherapy
• Tumor-related seizures should be treated with non-enzyme-inducing antiepileptic drugs such as levetiracetam and lacosamide to avoid chemotherapy interactions
• Paraneoplastic neurological syndromes are immune-mediated and may precede the diagnosis of the underlying cancer by months to years
• Anti-NMDA receptor encephalitis predominantly affects young women, is associated with ovarian teratoma, and presents with psychiatric symptoms, seizures, and movement disorders

Key Terms

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