Pineal cyst

What it means

The pineal gland is a tiny, pea-sized structure deep in the centre of the brain, best known for producing melatonin, the hormone that helps regulate your sleep-wake cycle. A pineal cyst is a small, fluid-filled pouch that forms within or alongside this gland. It is not a tumour or a sign that anything is growing abnormally — it is simply a fluid-containing space, similar in nature to a cyst you might find on a kidney or ovary.

Pineal cysts are one of the most common incidental findings on brain MRI. Studies find small pineal cysts in a substantial share of otherwise healthy people scanned for unrelated reasons, such as headaches or after a minor head injury. Most are small — under a centimetre — and stay that way for life.

Why it appears on a CT or MRI report

Because the pineal gland sits in the middle of the brain, it is almost always included in a standard brain MRI, and small cysts within it are easy to spot on the thin-sliced images modern scanners produce. The report will typically state the cyst's size in millimetres, note whether its wall is thin and smooth (typical of a simple cyst) or thickened and irregular, and comment on whether it presses on any nearby structure. CT is far less sensitive for this than MRI, so pineal cysts are more often first noticed on an MRI done for another reason.

What it usually means

The overwhelming majority of pineal cysts are simple, benign, and stable over time — considered a normal anatomical variant rather than a disease. Most people never know they have one, and it is not linked to headaches, seizures, or other symptoms in the vast majority of cases, even though the cyst is sometimes blamed for unrelated symptoms simply because it was seen on the same scan. Very rarely, a cyst grows large enough to press on the nearby channel that drains fluid from the brain's ventricles, which can cause headaches, vision changes, or, uncommonly, a build-up of fluid on the brain (hydrocephalus) — usually only with cysts larger than about 1.5 centimetres. Radiologists also confirm a cyst has the smooth, simple appearance expected of a benign cyst rather than features suggesting a rarer pineal tumour.

When to follow up

If your report describes a small, simple pineal cyst without pressure on surrounding structures, your doctor will usually recommend no treatment and, at most, a single follow-up MRI in a year or two to confirm it is stable — many radiologists don't recommend even that for small, classic-looking cysts. Seek prompt attention if you develop new or worsening headaches, especially ones that change with position or wake you from sleep, blurred or double vision, or unsteady walking, though these are far more often caused by something else entirely. Larger or atypical-looking cysts may warrant a referral to a neurologist simply to confirm the benign diagnosis.

A plain-language way to picture it

Think of the pineal gland as a small berry sitting at the very centre of the brain. A pineal cyst is like a tiny, water-filled blister on the surface of that berry — it doesn't change what the berry does, and it doesn't spread or invade anything around it. Most people carry one their whole life without ever knowing, the way many people have a small, harmless cyst on a kidney that never causes trouble. It's a passenger, not a problem.