Is a prominent cistern magma dangerous in any way? is it related to a normal pressure hydrocephalus

Not usually related: The cisterna magna is a spinal fluid space in the back of the brain which lies just posterior to the cerebellum. The space may be enlarged for a few reasons, both normal and pathologic (abnormal). You should have a MRI to evaluate further (if only CT done) and see Neurosurgeon or Neurologist for their opinion. Do you have any symptoms? Remember headaches can be from stress. Good luck.

No and No: It is a normal variant of no consequence and bears no relation to Normal Pressure Hydrocephalus