Differential Diagnosis: Posterior Fossa Mass

CHILD
Cerebellum/IVth Ventricle
- Medulloblastoma - midline, vermian or roof - usually hyperdense on plain CT - often enhance homogeneously
- usually PILOCYTIC ASTROCYTOMA - 2/3 are cystic with mural nodule - cyst fluid denser than CSF due to protein
- Ependymoma - INTRA-ventricular - "cast" of lumen - 50% are calcified
Brainstem
- Brainstem glioma - expands brainstem (infiltration w/o destruction) - hydrocephalus (may be late)
Extraaxial fluid collection
- Large cisterna magna ("Mega Cisterna Magna")
- Epidermoid inclusion cyst
- Arachnoid cyst (may bevel inner table of skull)
- Dandy Walker cyst of 4th ventricle
- Vermian agenesis
- Chronic subdural hematoma

ADULT
Extraaxial:
- Vestibular Schwannoma (CPA)
- Meningioma
- Ependymoma

Intraaxial:
- Metastasis - most common intraaxial neoplastic post fossa mass in adult
-Hemangioblastoma - cystic or solid - angio shows hypervascularity & stain
-Astrocytoma - usually not vascular on angio
-Medulloblastoma - often more lateral in adults