A pineal tumor in the quadrigeminal cistern can compresses the tectum of the midbrain. In addition to causing occlusion of the cerebral aqueduct and subsequent hydrocephalus in the lateral and third ventricles, it would also compress gaze centers. Can you see which two would be involved? Vertical and convergence. The loss of these gaze functions is called Parinaud's syndrome. The issue in this case however, is not with these centers but with the horizontal gaze center. Return to the case to try again.