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🧠 Brain Tumors — Complete USMLE Clinical Study Guide

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1. EPIDEMIOLOGY & OVERVIEW

High-yield mnemonic for mets: "Let Black Man Ride Constantly" — Lung, Breast, Melanoma, Renal, Colon

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2. WHO 2021 CLASSIFICATION (High-Yield)

Adult-Type Diffuse Gliomas

Pediatric-Type (also occur in adults)

• Diffuse intrinsic pontine glioma (DIPG) → now called Diffuse Midline Glioma, H3 K27-altered

Other Key Tumors

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3. HEREDITARY SYNDROMES (High-Yield for USMLE)

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4. CLINICAL PRESENTATION

General Features

• Headache in ~30% — typically dull, deep, worse with exertion/position change, may wake from sleep (10%)
• Classic triad (sleep disturbance + severe HA + N/V) is seen in a minority only
• Posterior fossa tumors: vomiting may precede headache by weeks
• Focal deficits: contralateral weakness/sensory loss, aphasia, visual field defects
• Seizures: often the presenting feature, especially with cortical/temporal tumors
• Personality/cognitive changes: frontal lobe involvement
• Increased ICP: headache worse with Valsalva (cough, sneeze, bending), papilledema, CN VI palsy (false localizing sign)

Localizing Clues

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5. SPECIFIC TUMOR PROFILES

🔴 Glioblastoma Multiforme (GBM) — Grade IV

• Location: Supratentorial (often temporal/frontal), can spread across corpus callosum → "butterfly glioma"
• Histology: Pseudopalisading necrosis, microvascular proliferation (endothelial hyperplasia), nuclear pleomorphism
• MRI: Ring-enhancing lesion with central necrosis, surrounding vasogenic edema
• Molecular: IDH-wildtype; EGFR amplification; TERT promoter mutation; loss of chr 10q
• MGMT methylation: Predicts better response to temozolomide (TMZ)
• Treatment: Maximal safe resection → concurrent RT + temozolomide (Stupp protocol) → adjuvant TMZ
• Prognosis: Median survival ~15 months with treatment; ~5% survive 5 years

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🟡 Oligodendroglioma — Grade 2–3

• Classic marker: IDH mutation + 1p/19q co-deletion
• Slow-growing; often presents with seizures in a young adult
• MRI: Cortical/subcortical, calcifications (50%), frontal lobe predilection
• Treatment: Surgery; chemotherapy (PCV — procarbazine, CCNU, vincristine) + RT for higher-grade
• Prognosis: Best among diffuse gliomas; median OS ~12–14 years (grade 2)

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🟠 IDH-Mutant Astrocytoma — Grade 2–4

• IDH mutation without 1p/19q co-deletion
• Grade 4 IDH-mutant astrocytoma ≠ GBM (different entity with better prognosis than GBM)
• CDKN2A/B homozygous deletion → upstages to grade 4
• Treatment: Surgery → RT + chemotherapy (temozolomide)

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🔵 Meningioma

• Origin: Dura mater — arachnoidal (meningothelial) cap cells
• Location: Cerebral convexities (parasagittal), skull base, spinal cord dorsum
• MRI hallmarks: Densely enhancing extra-axial mass + dural tail sign; no surrounding edema unless large
• Histology: Whorled pattern + psammoma bodies (calcifications)
• Molecular: NF2 mutation (chr 22) most common; TRAF7, KLF4, AKT1, SMO mutations in non-NF2
• WHO grades: I (benign, 92%) / II atypical (6%) / III malignant (2%)
• Risk factors: Female sex, NF2, prior cranial irradiation, increasing age
• Treatment:
  • Incidental/asymptomatic small → observe with serial MRI
  • Symptomatic or growing → surgical resection (curative if complete for grade I)
  • Incomplete resection or recurrence → external beam RT or stereotactic radiosurgery (SRS)
  • Chemotherapy/hormonal therapy: unproven (despite estrogen/progesterone receptor expression)

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🟢 Vestibular Schwannoma (Acoustic Neuroma)

• Origin: Schwann cells of vestibular portion of CN VIII
• ~9% of primary brain tumors
• Bilateral = pathognomonic for NF2
• Presentation: Progressive unilateral hearing loss, tinnitus, vertigo; late → brainstem/cerebellar compression
• MRI: Densely enhancing lesion, widens internal auditory canal, extends to cerebellopontine angle (CPA)
• Treatment: Observation / SRS (Gamma Knife) / microsurgical resection

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🟣 Medulloblastoma

• Most common malignant brain tumor in children
• Location: Posterior fossa — cerebellar vermis → obstructive hydrocephalus
• Presentation: Truncal ataxia, hydrocephalus, morning vomiting, papilledema
• Spreads: CSF seeding (leptomeningeal); must do spine MRI + lumbar CSF
• Molecular subgroups (WHO 2021): WNT-activated (best prognosis), SHH-activated, non-WNT/non-SHH (Groups 3, 4)
• Gorlin syndrome: PTCH1 mutation → desmoplastic medulloblastoma
• Treatment: Surgical resection + craniospinal RT + chemotherapy

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⚪ Craniopharyngioma

• Origin: Rathke's pouch remnant (adamantinomatous type) — suprasellar
• Affects children AND adults (bimodal peak: 5–14 yr, 50–74 yr)
• Presentation: Bitemporal hemianopia (optic chiasm compression), growth retardation, diabetes insipidus, hypopituitarism
• Imaging: Suprasellar calcification + cystic component (characteristic "motor oil" cysts)
• Treatment: Surgery ± RT; often complicated by endocrine deficits post-op

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⚫ Primary CNS Lymphoma (PCNSL)

• Immunocompromised (HIV/AIDS, organ transplant): EBV-driven, often multifocal
• Immunocompetent: DLBCL subtype; solitary periventricular lesion
• MRI: Homogeneous enhancement (vs. ring-enhancing in GBM); periventricular
• Key diagnostic clue: Lesion disappears with steroids ("ghost tumor") — avoid steroids before biopsy
• Treatment: High-dose methotrexate-based chemotherapy ± whole brain RT
• Do NOT treat with steroids first — it will yield a non-diagnostic biopsy

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🔴 Brain Metastases

• Most common intracranial malignancy
• Sources: Lung (most common overall), breast, melanoma, renal cell, colon
• Melanoma and renal cell: most likely to be hemorrhagic
• Multiple lesions: Strongly suggests mets over primary tumor
• Location: Gray-white junction (hematogenous spread)
• MRI: Ring-enhancing, surrounded by vasogenic edema; often multiple
• Treatment: Whole brain RT, SRS (for limited lesions), surgery (single accessible met), targeted therapy if driver mutation (e.g., EGFR in NSCLC, BRAF in melanoma)

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6. DIAGNOSIS

Neuroimaging

• CT: Quick screen; good for calcifications and hemorrhage
• MRI with gadolinium: Gold standard — identifies blood-brain barrier breakdown (enhancement)
• MR spectroscopy: ↑ choline, ↓ NAA → favors high-grade tumor; presence of lipid/lactate peak → necrosis
• Perfusion MRI (rCBV): Higher in high-grade gliomas
• PET: Distinguishes tumor recurrence vs. radiation necrosis

CSF

• Indicated for leptomeningeal spread (medulloblastoma, PCNSL, mets)
• Cytology: malignant cells in carcinomatous meningitis
• Contraindicated with elevated ICP/mass effect (herniation risk)

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7. MANAGEMENT OVERVIEW

Acute Management

• Dexamethasone: First-line for vasogenic edema (↓ VEGF-driven permeability) — dramatic temporary relief
• Seizures: Levetiracetam (preferred); phenytoin no longer recommended prophylactically
• Elevated ICP: Elevate HOB 30°, mannitol/hypertonic saline, hyperventilation (bridge), VP shunt if hydrocephalus

Definitive Treatment

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8. HIGH-YIELD USMLE MNEMONICS & ONE-LINERS

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9. PEDIATRIC vs. ADULT — LOCATION RULE

• Adults: Supratentorial (cerebral hemispheres) — most primary and metastatic tumors
• Children: Infratentorial (posterior fossa) — medulloblastoma, pilocytic astrocytoma, ependymoma (4th ventricle), DIPG

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10. RECENT UPDATES (2024–2025)

• ESTRO-EANO 2025 guideline (PMID 39454886): Updated radiotherapy target delineation for IDH-mutant WHO grade 2–3 diffuse gliomas — incorporates FLAIR-based contouring
• WHO 2021 CNS classification fully adopted: Molecular profiling (IDH, 1p/19q, MGMT, H3 K27) is now standard of care and required for definitive grading
• GBM molecular advances (PMID 40542948): TTFields (tumor-treating fields) now part of standard GBM management; trials ongoing with checkpoint inhibitors and CAR-T

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1. Epidemiology — what's most common and when
2. WHO 2021 Classification — the molecular-based system you must know
3. Hereditary syndromes — NF1/2, TSC, VHL, Li-Fraumeni, etc.
4. Clinical presentation — by general features and location
5. Individual tumor profiles — GBM, oligodendroglioma, meningioma, schwannoma, medulloblastoma, craniopharyngioma, PCNSL, and brain mets
6. Diagnosis — imaging patterns, MRI features, CSF
7. Management — acute (dexamethasone, seizure control) + definitive (surgery/RT/chemo)
8. USMLE mnemonics — one-liner pattern recognition table
9. Peds vs. adult location rule
10. 2024–2025 updates — WHO 2021, TTFields, new RT guidelines

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🪱 Neurocysticercosis (NCC) — Crisp MBBS Study Notes

Note: Nelson's Textbook of Pediatrics is not in the library, but the content below is compiled from equivalent authoritative pediatric-infectious-disease sources (Red Book principles, Bradley & Daroff, Grainger & Allison diagnostic radiology, Tintinalli, IDSA 2018 guidelines) — all directly relevant to MBBS/pediatric level.

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1. THE CONCEPT IN ONE LINE

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2. LIFECYCLE — THE KEY TO UNDERSTANDING EVERYTHING

PORK TAPEWORM (Taenia solium)
         ↓
  TWO ways to get infected:

① TAENIASIS (intestinal worm):
   Eat undercooked PORK with larvae (cysticerci)
   → Adult worm lives in human gut → eggs passed in feces
   → Person is a DEFINITIVE HOST

② CYSTICERCOSIS / NCC:
   Ingest T. solium EGGS (feco-oral route / contaminated food/water)
   → Eggs hatch → oncospheres → penetrate gut wall
   → Hematogenous spread to BRAIN, muscle, eye, skin
   → Form CYSTICERCI (larvae with scolex)
   → Person is an INTERMEDIATE HOST

Key concept: You get NCC from eggs (not from eating pork). You can get it from a tapeworm carrier in your household even if you're vegetarian!

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3. EPIDEMIOLOGY

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4. PATHOLOGY — 4 STAGES OF THE CYST

USMLE/MBBS pearl: Most seizures occur at stages 2 & 3 — when the dying larva triggers the inflammatory cascade. 80–90% of single lesions resolve in 3–6 months.

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5. FORMS OF NCC

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6. CLINICAL FEATURES

• Usually simple partial (focal) with secondary generalization
• Occur as cyst degenerates (stages 2–3)

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7. DIAGNOSIS

Imaging (cornerstone)

• Calcified lesions (end-stage) — hyperdense dots
• Cystic hypodense lesions ± scolex

• "Hole with dot" sign = cyst + scolex = pathognomonic
• Ring-enhancing lesions with perilesional edema in colloidal stage
• FLAIR: scolex appears hyperintense
• Identifies all 4 stages clearly

Serology

• EITB (Enzyme-Linked Immunoelectrotransfer Blot) on serum — most specific (~99%)
• Less sensitive with single/calcified cysts
• CSF ELISA also used

CSF

• May show eosinophilia, elevated protein, low glucose (basal form)
• Rarely needed; lumbar puncture contraindicated if ↑ ICP

Del Brutto Diagnostic Criteria (2017 IDSA/ASTMH)

• Absolute criterion: Histopathology OR cyst with scolex on imaging
• Major criteria: Imaging lesions compatible with NCC + positive serology
• Minor criteria: Hydrocephalus, enhancement, clinical features, exposure history

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8. TREATMENT

Framework: Match treatment to stage + form + number

Drug Details

Why steroids with antiparasitics? Killing the larvae triggers a surge of host inflammation → can cause cerebral edema, increased ICP, paradoxical worsening. Steroids blunt this.

Albendazole > Praziquantel because praziquantel levels are reduced by dexamethasone and by coadministration with antiepileptics (enzyme induction).

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9. SINGLE ENHANCING LESION (SEL) — High-yield for India/Pediatrics

• Most common presentation in India and pediatric patients
• 1–2 cm ring-enhancing or disc-enhancing lesion on CT/MRI
• Differential: NCC vs. tuberculoma (both common in India!)
• NCC favored if: scolex visible, no basal meningeal enhancement, EITB positive
• Tuberculoma favored if: satellite lesions, basal enhancement, contact with TB
• SEL resolves in 80–90% within 3–6 months with albendazole + steroids

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10. COMPLICATIONS

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11. PREVENTION

• Proper cooking of pork (>65°C destroys cysticerci)
• Handwashing and good hygiene (breaks feco-oral transmission of eggs)
• Sanitation — toilet access, no open defecation
• Mass drug administration: albendazole/praziquantel in endemic areas (experimental)
• Porcine vaccination: Ox-fax vaccine against T. solium in pigs

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12. MEMORY HOOKS

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