Rarely. There are case reports in the medical literature of pineal tumors causing psychosis. That means it happens so rarely that when it does, someone writes a paper about it!
Yes. It is possible. Pineal tumors can be associated with alterations in hormone levels that could lead to psychosis. But it isn't very common.
Rare but true. Pineal tumors can have a wide variety of signs and symptoms in the way they present. Though rare, psychosis can be on of the presentations that occurs. Because of that if you have concern you should discuss them with your doctor right away so that your doctor can order the proper tests to get you diagnosed.
I'm no surgeon, but. I don't think so. Before the VP shunt is placed, the pt would have sxs of increased pressure: vision changes, balance problems, headache, etc. After the shunt, those sxs should abate. Psychosis is hearing voices, seeing things that aren't there, held beliefs despite evidence to the contrary; and should not be related to a pineal tumor.
Not Generally. Pineal tumors do not typically cause psychoses. However a large tumor can affect the level of wakefulness and may affect thinking, concentration, etc.