Very early signs of a posterior fossa tumor can include drowsiness, headaches, imbalance, ataxia (or an uncoordinated walk), nausea and vomiting. Other symptoms of a posterior fossa tumor occur when the tumor damages nearby structures in the brain such as the cranial nerves. Symptoms associated with cranial nerve damage include: dilated pupils, eye problems, facial muscle weakness, hearing loss, loss of feeling in part of the face, problems with taste, ataxia and vision problems.
Because of where these tumors are located, they often grow to block the flow of cerebrospinal fluid. This causes a condition of increased pressure inside the skull called hydrocephalus, which in turn produces symptoms include headaches, nausea and vomiting.