**Question:** Most common brain tumour is

A. Glioma
B. Meningioma
C. Pituitary adenoma
D. Ependymoma

**Core Concept:** Brain tumours are classified based on their origin and characteristics. Brain tumours can be either primary (originating from brain cells) or secondary (spreading from other parts of the body). The common types include gliomas, meningiomas, pituitary adenomas, and ependymomas.

**Correct Answer: D. Ependymoma**

Ependymomas are a type of primary brain tumour that arises from ependymal cells, which line the ventricles and theependymal layer of the central canal of the spinal cord. They are less common than gliomas and meningiomas but still represent a significant proportion of brain tumours.

**Why the Correct Answer is Right:** Ependymomas are often misdiagnosed as other types of brain tumours due to their rarity and variable presentation. They can be classified into three groups:

1. Subependymal: These tumours develop in the ventricles and can cause obstructive hydrocephalus. They are often associated with the R132H mutation in the IDH1 gene, which is a reliable genetic marker for these tumours.
2. Intramedullary spinal cord: These tumours arise from ependymal cells in the spinal cord and present with motor and sensory deficits, depending on the spinal cord level involved.
3. Intracranial extraventricular: These tumours arise outside the ventricles but still affect the brain parenchyma, causing symptoms related to brain dysfunction.

**Why Each Wrong Option is Incorrect:**

**A. Glioma:** Gliomas are a broader term for tumours originating from glial cells (astrocytes, oligodendrocytes, and ependymal cells). They can be further classified into various grades (I-IV) based on their malignant potential and can affect various regions of the brain. While gliomas are a different type of brain tumour, ependymomas are a distinct entity and should not be considered the same.

**B. Meningioma:** Meningiomas are benign tumours that originate from the meninges (meninges) and are not related to ependymal cells.

**C. Pituitary adenoma:** Pituitary adenomas are tumours of the pituitary gland, a neuroendocrine structure located in the sella turcica. They are not related to ependymal cells and are classified differently from ependymomas.

**Clinical Pearls:**

Ependymomas may present with various symptoms depending on the location and size of the tumour. Common symptoms include seizures, headache, focal neurological deficits, and increased intracranial pressure. Ependymomas are often misdiagnosed as other types of brain tumours due to their rarity and diverse clinical presentations.

By correctly identifying the type of brain tumour and its specific characteristics, one can differentiate it from other types of brain tumours and plan an appropriate treatment strategy.