6 The “cyst with a mural nodule” morphology is suggestive of a less-aggressive etiology such as a pilocytic astrocytoma, ganglioglioma, pleomorphic xanthoastrocytoma (PXA), or hemangioblastoma. Metastases can be cystic; however, other neoplasms such as medulloblastoma are rarely predominantly cystic. Infectious etiologies such as cysticercosis can also cause cysts in the cerebellum. Ganglioglioma and PXA are more common in the supratentorial brain. However, within the posterior fossa, the configuration of a cyst and mural nodule narrows the differential consideration mainly to juvenile pilocytic astrocytoma (JPA) or hemangioblastoma (Table 6.1). (See Chapters 1 and 5 as supplements to this chapter.)
Posterior Fossa Cystic Neoplasms
| Juvenile Pilocytic Astrocytoma | Hemangioblastoma | |
|---|---|---|
| CT | Hypoattenuating cystic component with hypoattenuating to isoattenuating mural nodule with avid contrast enhancement | Hypoattenuating cyst and isodense nodule with avid contrast enhancement |
| T1WI | Well-demarcated lesion Solid component: Isointense to hypointense relative to normal brain Cystic component follows fluid signal intensity. | Well-demarcated lesion Nodule peripherally located near pial surface and isointense to gray matter on T1WI Cyst: Isointense or slightly hyperintense on T1WI compared with CSF |
| T2WI | Nodule: Hyperintense to normal brain with minimal surrounding T2WI signal Cyst: Follows fluid signal | Nodule: Hyperintense Cyst: High signal intensity |
| Vascularity/ Enhancement |
