**Core Concept**
Posterior cranial fossa tumours are a group of neoplasms that arise from the structures within the posterior cranial fossa, including the cerebellum, brainstem, and cranial nerves. These tumours can be benign or malignant, and their location and characteristics determine their clinical presentation and management.

**Why the Correct Answer is Right**
The posterior cranial fossa is home to several types of tumours, including medulloblastomas, ependymomas, and pilocytic astrocytomas. These tumours arise from the glial cells or neural tissue within the cerebellum and brainstem. The correct answer is a type of tumour that is not commonly found in the posterior cranial fossa.

**Why Each Wrong Option is Incorrect**
**Option A:** Medulloblastoma - This is a common type of posterior cranial fossa tumour, especially in children, and arises from the cerebellum.

**Option B:** Meningioma - Although meningiomas can occur in the posterior cranial fossa, they are more commonly found in the anterior cranial fossa, near the base of the skull.

**Option C:** Glioblastoma - This is a type of high-grade glioma that can occur in the posterior cranial fossa, but it is less common than other types of tumours in this location.

**Option D:** Schwannoma - This is a type of tumour that arises from the Schwann cells that surround the cranial nerves, and it can occur in the posterior cranial fossa, especially near the cerebellopontine angle.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with a posterior cranial fossa tumour, it is essential to consider the clinical presentation, including symptoms such as ataxia, cranial nerve palsies, and hydrocephalus, as these can provide clues to the location and type of tumour.

**Correct Answer:** B. Meningioma