What are some diagnostic possibilities?
The combination of findings are not typical of the usual lesions of this site. Pineal cysts are common, and rarely do haemorrhage, and must therefore be considered high on the differential. Pineal parenchymal tumours must also be considered, although they typically have more solid component. Both pineocytomas and germinomas can however be largely cystic. Entirely intraventricular craniopharyngioma, pilocytic astrocytoma of the third ventricle are other possibilities.
Centred on the posterior third ventricle in the midline, inseparable from the pineal, is a 31 x 21 x 21 cystic mass with a fluid/fluid level with supernatant effect with blood product in the dependent portion, and T1 hyperintense anterior compartment. Thickened septations lie within the cyst, and do not enhance. Apart from some subtle capsule enhancement, there is no definite enhancing component.
The mass causes compression of the cerebral aqueduct-the degree of hydrocephalus has been decreased by placing a right ventricular shunt catheter since the earlier CT scan. The third ventricle anterior to the mass is distended and contains water density CSF. The vein of Galen and internal cerebral veins are displaced superiorly.
No other intracranial mass lesions, or abnormal enhancement is shown.