Posterior cranial fossa tumors have a very different differential in an adult as opposed to a child.

Adult

• intraventricular

  • posterior fossa ependymoma

    • usually group B

    • usually arises from the floor of the 4^th ventricle

  • subependymoma

    • most frequently near the obex

    • often in older patients

  • choroid plexus papilloma

    • strikingly vividly enhancing

• intra-axial

  • cerebellar metastases

    • most common parenchymal posterior fossa tumor in adults

    • especially lung cancer and breast cancer

    • also melanoma, thyroid malignancies, and renal cell cancer

    • gastrointestinal stromal tumor (very rare) ⁵

  • hemangioblastoma

    • most common parenchymal posterior fossa primary brain tumor in adults

    • prominent flow voids are often present

  • lymphoma ⁴

  • Lhermitte-Duclos disease​

  • medulloblastoma

    • most often SHH-activated

    • heterogeneous tumors in the cerebellar hemisphere

  • rosette-forming glioneuronal tumor (RGNT)

    • frequently in the superior vermis

• extra-axial

  • schwannoma: most commonly of the vestibular nerve

  • meningioma

  • epidermoid cyst

  • lipoma ⁴

An important space-occupying lesion (the most common in fact) to remember is that of a stroke, which when subacute can mimic a tumor. 

Child

• medulloblastoma: most common (30-40%) ⁷

  • hypercellular tumor (diffusion restriction with low ADC values ~550 x 10^-6 mm²/s, hyperdense on non-contrast CT)

  • they do not usually extend into the basal cisterns through the foramina of Luschka and foramen of Magendie

  • drop metastases and leptomeningeal spread are common at presentation

• pilocytic astrocytoma: second most common (25-35%) ⁷

  • large cystic component

  • brightly enhancing mural nodule

• brainstem glioma (20-25%) ⁷

• posterior fossa ependymoma (10-15%) ⁷

  • usually group A

  • usually arises from the lateral recess of the 4^th ventricle

  • protrudes out of the foramina of Luschka and foramen of Magendie

  • does not usually cause significant diffusion restriction

• atypical teratoid/rhabdoid tumor (AT/RT) (1-2%) ⁷

  • young children - median age is less than 2-3 years ⁸

  • very agressive

• hemangioblastoma (uncommon except in patients with vHL)

• teratoma (in infants)

A quick and handy mnemonic for posterior fossa tumors in children is BEAM.

Distribution

Although it is true that posterior fossa tumors are much more common in children than in adults the distribution does vary with age ²:

• 0 to 3 years of age: supratentorial > infratentorial

• 4 to 10 years of age: infratentorial > supratentorial

• 10 to early adulthood: infratentorial = supratentorial

• adults: supratentorial > infratentorial

Overall 50-55% of all brain tumors in children are found in the posterior fossa ³.