What is the most likely pathology of the cystic pineal mass? Is there a differential?
This almost certainly represents an benign pineal cysts. The differential that is usually included is of a cystic tumour, usually a pineocytoma, although in the absence of any atypical features (thicker wall, nodular enhancement, septae etc..) it should not be considered.
A cystic pineal region mass (yellow dotted line) has prolapsed anteriorly and obstructed the superior aspect of the aqueduct (red). Hydrocephalus is present with inferior bowing of the floor of the third ventricle and ballooning of the supraoptic recess (blue) and infundibular recess (purple).
As is the cases with all pineal gland masses the internal cerebral veins (orange) are located above the mass.