Where is the main abnormality located and what complication is evident?
A large pineal region mass is present which results in hydrocephalus, due to compression of the aqueduct.
Look carefully. Is a second related abnormality present?
Yes, most easily seen on sagittal images, a second smaller but similar mass is present in the floor of the third ventricles / suprasellar region.
What should be your favoured diagnosis?
Germ cell tumour has a tendency to involve these two sites simultaneously.
A large lobulated mass is centered on the pineal gland, engulfing the pineal calcifiation. It is somewhat hyperdense compared to adjacent brain. A further smaller mass is seen in the floor of the third ventricle. The midbrain is distorted, compressed and demonstrates low density suggestive of oedema. Obstructive hydrocephalus is present.