Posterior Fossa Tumors

Front 1

Medulloblastoma

Back 1

Usualy before age 10 and greater in males.
Majority arise from the cerebellar vermis
Extension into the adjacent fourth ventricle and subsequent development of hydro is common.
In older kids and adults tends to be more lateral within the cerebellar hemispheres.
Highly malignant Grade 4 with rapid growth.
Subarachnoid CSF spread common at time of dx.
Most manifest as solid, hyperdense masses on CT
On MR hypointense on T1 and variable on T2.
After contrast demonastrates intense but heterogeneous contrast.

Front 2

Pilocytic Astrocytoma

Back 2

Most common location is the cerebellum.
Most patients present before 20 years of age.
Most common tumor seen in Neurofibromatosis type 1
WHO grade 1
Most are cystlike with an enhancing mural nodule. Some are solid masses with or without a necrotic center.
CT well-demarcated with the solid portion being isodense or hypodense to brain tissue.
On MR they are isointense or hypointense compared to grey matter on T1 and hyperintense on T2.
Cystic portion contains proteinaceous fluid and does not exactly follow the signal intensity of CSF.
Mural nodule of the cystic forms enhances intensely, while teh solid component of the noncystic forms enhances to some degree but is more variable in intensity.

Front 3

Ependymoma

Back 3

The tumor arises from the ependymal cells taht line the ventricular system and the central canal of the spinal cord.
In kids mostly see in posterior fossa with most centered within the fourth ventricle.
WHO grade 2
When tumor arises from 4th ventricle, frequently extends through the foramina of luschka or magendie into the CPA.
On CT, isodense with a mix of calcification, cystic change and even hemorrhage, producing an overall heterogeneous appearance ( also on MR)
After contrast, heterogeneous enhancement of the solid component.
Extraventricular extension from the 4th ventricle through the adjacent foramina is high characterisitic.

Front 4

Brainstem glioma

Back 4

Majority are astrocytomas and are grade 1 or 2.
1. exophytic growth into the adjacent cisternal spaces.
2. If the ventral portion of the pons extends beyond the anterior margin of the basilar artery, then abnormal enlargement of the pons is present.
3. Alteration of the normal fourth ventricle contour provides a useful clue.
On CT, manifests as a focal, hypodense to isodense expansion of the brainstem.
On MR, typical prolongation of T2 and T2 is seen.
Most common in pons.
Between 3 and 10 years old.

Front 5

Capillary hemangioblastomas

Back 5

Most common in young and middle aged adults. Most common primary cerebellar neoplasm int he adult population.
Well defined cystic mass with an intensely enhancing mural nodule. Since the tumor nidus receives its blood supply from the pia mater, the nodule is always superficial in location.
On MR, cystlike masses with hypointensity on T1 and hyperintensity on T2.