Tumors that arise from cells in the pineal gland are known as pinealomas. As the pineal gland is located in the posterior third ventricle, pineal tumors often present with non-communicating hydrocephalus due to compression of the cerebral aqueduct. In addition, downward pressure may compress the dorsal midbrain, resulting in a Parinaud's syndrome (lid retraction, large pupils that react poorly to light, impaired upgaze, and convergence retraction nystagmus).