Pineal cysts are fluid-filled sacs that form in the pineal gland, a small endocrine gland in the brain that produces melatonin, a hormone that regulates sleep-wake cycles. Most pineal cysts are harmless and do not cause any noticeable symptoms, but some can be problematic if they grow large or exert pressure on nearby structures in the brain. The possible symptoms of pineal cysts may include:

• Headaches: Some people with pineal cysts may experience recurrent headaches, especially in the back of the head or behind the eyes. ^{1 8}
• Vision problems: Pineal cysts can compress the tectum, a part of the brain that controls eye movements, or the optic nerve, which carries visual information from the eyes to the brain. This can lead to visual disturbances such as double vision, blurred vision, difficulty focusing, or loss of peripheral vision. ^{1 4}
• Sleep disturbances: Pineal cysts can interfere with the production of melatonin, which helps regulate the circadian rhythm of sleep and wakefulness. This can result in sleep problems such as insomnia, excessive daytime sleepiness, or altered sleep patterns. ^{7 4}
• Behavioral changes: In rare cases, pineal cysts may affect the limbic system, a part of the brain that is involved in emotions, memory, and motivation. This can cause mood swings, personality changes, anxiety, depression, or cognitive impairment. ^{1 4}