Where is the main abnormality located?
A large rounded mass is present in the posterior fossa, appearing to arise form the vermis, displacing the 4th ventricle anteriorly.
What is a third ventriculostomy?
A third ventriculostomy is type of surgical treatment for obstructive hydrocephalus, especially when the obstruction is located at the level of the aqueduct of Sylvius (e.g. aqueduct stenosis). A permanent defect is created in the floor of the third ventricle anterior to the mamillary bodies, thus connecting the third ventricle with the interpeduncular cistern.
There is a large posterior fossa mass, located in the midline, with faint speckled calcification anteriorly. It appears isodense with grey matter. The 4th ventricle appears displaced anteriorly. Anterior pneumocephalus consistent with recent intervention.