Findings:
There is a large cystic lesion in the cerebellum involving the vermis and medial left cerebellar hemisphere which measures 4.0 x 3.6 x 4.4 cm in the greatest, AP, transverse, and CC dimensions. There is an approximately 1cm solid mural nodule in the superolateral aspect of the lesion on the left, best seen in the coronal projection.

There is a beam hardening artifact through the posterior fossa related to multiple ear piercings. There is effacement of CSF spaces in the posterior fossa, particularly the prepontine cistern and cerebellopontine angles, as well as compression of the caudal cerebral aqueduct and fourth ventricle. There is resultant obstructive hydrocephalus with enlargement of the third and lateral ventricles. There is transependymal flow of CSF suggesting an acute process. There is downward bowing of the floor of the third ventricle with effacement of the suprasellar cistern. There is both upward transtentorial and downward tonsillar herniation. The supratentorial sulci are symmetrically small, at least partially effaced.

Impression:
Large cystic mass in the posterior fossa with solid mural nodule, concerning for a hemangioblastoma. The lesion causes obstructive hydrocephalus due to compression of the fourth ventricle, with lateral and third ventriculomegaly and transependymal fluid migration. There is both upward transtentorial and downward tonsillar herniation.

Recommendations:
For your training purposes, recommendations are not included in this report.