Causes & Risk Factors
Posterior fossa tumor
A posterior fossa tumor is a tumor at the back of the brain that commonly causes hydrocephalus by blocking the fourth ventricle.
In short: Posterior fossa tumor
- It is located at the back of the brain, near the fourth ventricle.
- It commonly obstructs CSF flow, causing hydrocephalus.
- Most posterior fossa tumors present with some hydrocephalus.
- Treatment addresses both the tumor and the hydrocephalus.
What it is
A posterior fossa tumor is a tumor located in the posterior fossa — the space at the back and base of the brain containing the cerebellum and brainstem, near the fourth ventricle. Such tumors are common in children.
Understanding Posterior fossa tumor
Because the posterior fossa contains the fourth ventricle and the nearby cerebral aqueduct, a tumor here can readily block CSF flow, causing obstructive hydrocephalus. Studies suggest that about 85% of children with posterior fossa tumors present with some degree of hydrocephalus, and roughly 20–30% develop permanent hydrocephalus requiring ongoing treatment. Management addresses both the tumor (often with surgery) and the hydrocephalus; removing the tumor can relieve the obstruction in many cases, while some children also need CSF diversion such as a shunt or ETV.
Why it matters
Understanding posterior fossa tumors helps families see why tumors at the back of the brain so often cause hydrocephalus, and why care addresses both the tumor and the resulting CSF blockage.
Common questions
Where is a posterior fossa tumor?
At the back of the brain, near the fourth ventricle.
Why does it commonly cause hydrocephalus?
It can block CSF flow at the fourth ventricle.
Does removing it relieve the hydrocephalus?
Often, though some children also need CSF diversion.
Bottom line
A posterior fossa tumor commonly causes hydrocephalus by blocking the fourth ventricle, with treatment addressing both the tumor and the CSF blockage.
Browse all 265 Hydrocephalus definitions
Read the Hydrocephalus patient guides
Not sure which page you need? Put words to it with the symptom navigator