The pineal gland is the only part of the brain that is normally calcified and can thus be seen on a skull x-ray as distinct from the other parts of the brain.
This otherwise rather obscure and seemingly useless fact was important in the days before the widespread adoption of CT Scans. Back then, as an old radiologist told me, locating the pineal gland on plain skull X-rays was one of the ways to help orientatate a lesion or foreign body within the skull -- the pineal gland should normally be in the midline and roughly in the center of the skull.
Similarly, if the pineal gland is shifted off midline, it's likely that a space-occupying lesion exists somewhere in a position to push the pineal gland off center.