Focal tumors are defined as:
- Involving less than 50% of the afflicted anatomical structure or
- Less than 2 cm in maximum diameter
- Absence of hypodensity
There are three regions where these focal tumors can be found:
2. Tectum of the midbrain
3. At the cervicomedullary junction
- Most commonly involve the midbrain and medulla.
- Usual pathology is juvenile pilocytic astrocytoma (WHO grade I).
MR scan below shows a dorsally exophytic tumor (1) of the brain stem