Posterior fossa tumours

Posterior fossa tumour has a very different differential in an adult as opposed to a child.

Adult

• cerebellar metastases (most common)
  • especially lung cancer and breast cancer
  • also melanoma, thyroid malignancies, and renal cell cancer
• haemangioblastoma: most common primary brain tumour
• astrocytomas and medulloblastomas are rare in the posterior fossa of adults (<1% all tumours)

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

Child

• posterior fossa astrocytoma
  • pilocytic astrocytoma: most common
  • brainstem glioma
• medulloblastoma: (also known as posterior fossa PNET)
• ependymoma
• atypical teratoid/rhabdoid tumour (AT/RT)
• haemangioblastoma (uncommon except in patients with vHL)
• teratoma (in infants)

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

Although it is true that posterior fossa tumours 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 adult hood: infratentorial = supratentorial
• adults: supratentorial > infratentorial

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