How brain tumors are tested on Step 1

Age first, then location, then histology.

AdultsMostly supratentorialMetastases most common overallGlioblastoma (malignant)Meningioma, schwannoma (benign)Pituitary adenoma, oligodendrogliomaChildrenMostly infratentorial (posterior fossa)Pilocytic astrocytoma (benign)Medulloblastoma (malignant)EpendymomaCraniopharyngioma (supratentorial)vs
Age and location. Brain tumors are the most common solid tumors of childhood.

Adult tumors

Location and histology identify the tumor.

TumorLocation and imagingHistology and markers
MetastasesMultiple, gray-white junction, edemaResemble the primary cancer
GlioblastomaCerebral hemisphere; crosses corpus callosum; ring enhancingPseudopalisading necrosis, vascular proliferation; GFAP+
OligodendrogliomaFrontal lobe; calcified; seizures"Fried egg" cells, "chicken wire" capillaries; 1p/19q codeletion
MeningiomaDural-based, compresses brain; dural tailWhorls, psammoma bodies
Vestibular schwannomaCerebellopontine angleAntoni A and B areas, Verocay bodies; S-100+
HemangioblastomaCerebellum; von Hippel-LindauFoamy cells, capillaries; can make EPO (polycythemia)
Pituitary adenomaSella; bitemporal hemianopiaProlactinoma most common

Primary brain tumors rarely spread outside the CNS.

Pediatric tumors

Most arise in the posterior fossa and cause ataxia or hydrocephalus.

  • Pilocytic astrocytoma: most common benign pediatric brain tumor; cerebellar cyst with a solid nodule; Rosenthal fibers; excellent prognosis after resection.
  • Medulloblastoma: malignant tumor of the cerebellar vermis; truncal ataxia; small round blue cells with Homer Wright rosettes; can spread through CSF ("drop metastases").
  • Ependymoma: fourth ventricle; blocks CSF flow (hydrocephalus); perivascular pseudorosettes.
  • Craniopharyngioma: above the sella from Rathke pouch remnants; calcified cyst with "motor oil" fluid; bitemporal hemianopia, growth failure.

Raised intracranial pressure and herniation

A growing mass shifts brain tissue past rigid dural folds.

SubfalcineCingulate gyrus under the falx; compresses ACA → legweaknessUncalMedial temporal lobe; CN III (blown pupil), PCA,contralateral hemiparesisCentralDownward brainstem shift; Duret hemorrhages in theponsTonsillarCerebellar tonsils into foramen magnum; respiratoryarrest
Herniation. Cushing triad (hypertension, bradycardia, irregular breathing) signals raised intracranial pressure.

Worked example

Age, site, and histology.

functions Worked example — a child with clumsy walking

An 8-year-old has headaches and a wide-based, unsteady gait. MRI shows a cystic mass in the cerebellar hemisphere with an enhancing mural nodule. Biopsy shows eosinophilic, corkscrew-shaped fibers. What is the tumor and the prognosis?

  1. A child with a posterior fossa mass suggests pilocytic astrocytoma, medulloblastoma, or ependymoma.
  2. A cyst with a mural nodule is the classic imaging appearance of pilocytic astrocytoma.
  3. Corkscrew eosinophilic fibers are Rosenthal fibers.
  4. This low-grade tumor is often cured by surgical removal.

Answer. Pilocytic astrocytoma; good prognosis after resection.