Is a cavum septum pellucidum abnormal?

In an adult it is a normal anatomical variant. Everyone has one before birth; it usually closes in the first months of life and in some people it does not. Found on its own it needs no action.

No. It is a fluid space between the two leaves of a thin membrane, not an enclosed sac with a wall of its own. Reports sometimes use the word cyst for an unusually large one, which is a description of size rather than a change of category.

Can it cause symptoms?

Not in the ordinary case. Very rarely a large cavum is described alongside signs that it is interfering with cerebrospinal fluid flow, and a report states that explicitly when it applies. Otherwise it is not the explanation for headaches or anything else.

My pregnancy scan mentioned the cavum septi pellucidi. Is that the same thing?

The same structure, the opposite question. On a fetal scan it should be present, and seeing it is a routine confirmation that the midline has formed normally; its absence is what prompts a closer look. That is a conversation for the team who performed the scan.

I have read it is linked to head injuries. Should I be worried?

A persistent cavum has been studied as a group-level marker in populations with repeated head impacts. A statistical association in a study population does not tell one person with an incidental finding anything about themselves, and it is not a reason for investigation on its own.

Findings explained

What “cavum septum pellucidum” means on a brain scan

Read Your Scan Editorial Team·Last updated 7 September 2026·5 min read

Written from published radiology references and reviewed for plain language. Not written or signed by a physician, and not a diagnosis. How we write these pages →

Axial FLAIR MRI of the brain at the level of the lateral ventricles — A real axial FLAIR slice at the level of the lateral ventricles. The septum pellucidum is the thin midline partition between the two dark ventricles; a cavum is a small fluid space between its two leaves.Real exam · 511KeV · CC BY-SA 4.0

The short answer

The septum pellucidum is a thin double membrane separating the two fluid-filled ventricles at the centre of the brain. A cavum septum pellucidum is a small space between its two leaves. In an adult it is a normal anatomical variant, present in a minority of people, and on its own it means nothing about health.

It is a gap between two membranes, not a cyst, a lesion or damage.
Everyone has one before birth. It usually closes in the first months of life, and in some people it simply does not — which is why it is a variant rather than an abnormality.
Found on an adult brain MRI with nothing else, it needs no action and no follow-up.
It is looked for on fetal scans for a completely different reason: its absence can point to a problem with how the midline of the brain formed.
A related space slightly further back is called a cavum vergae, and the two are often reported together.

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What the structure is

At the centre of the brain sit two lateral ventricles, mirror-image chambers filled with cerebrospinal fluid. Between them is a thin partition called the septum pellucidum — literally the translucent wall. It is not one membrane but two, laid against each other.

A cavum septum pellucidum is a space between those two leaves, filled with fluid. That is the entire finding. It is a gap in a partition, not something growing, not something lost, and not something pressing on anything.

A cavum vergae is the same kind of space continuing slightly further back, and the two are frequently reported in the same sentence. It has the same meaning.

Axial CT of a normal brain at the level of the orbits and skull base — A normal head CT. The structure is small and central, which is why it is described only in passing and only when a space is present.Real exam · Mikael Häggström, M.D. · CC0 1.0

Why some adults have one and most do not

Every fetus has one. The two leaves of the septum are separated during development, and they normally fuse from back to front around the time of birth and in the first few months of life. In a proportion of people that fusion is incomplete, and the space simply persists into adulthood.

That is the whole explanation for why it appears on some reports and not others. It is a developmental variant with no consequence, in the same category as any of the ordinary anatomical differences a scan reveals. Estimates of how many adults have one vary with how it is measured and how good the scanner is.

On an adult scan, on its own

Reported as an isolated finding on a brain MRI or CT, it needs nothing: no follow-up scan, no referral, no restriction. It is mentioned because the report describes what is visible, and because naming it tells the next reader that the midline was examined and understood.

It does not cause headaches, dizziness or memory problems.
It does not obstruct the flow of cerebrospinal fluid. Very rarely a large one is described together with signs that it is, and in that case the report says so specifically.
It is not a cyst in the sense people fear — nothing is enclosed in a wall of its own and nothing is growing.
A report that mentions it and nothing else has, in effect, described a normal brain.

The one place the term appears in a different context is research: a persistent cavum has been studied as a marker in populations with repeated head impacts, and in some psychiatric research. Those are group-level statistical associations in study populations, and they do not translate into a meaning for one person who happens to have one on a scan.

Why it is looked for on a pregnancy scan — a different question

A large share of the searching for this phrase comes from a completely different situation, and it deserves a straight answer rather than being folded into the adult one.

On a fetal anomaly scan, the sonographer checks that a cavum septi pellucidi is PRESENT. At that stage it should be there, and seeing it is one of the routine confirmations that the midline structures of the brain have formed as expected. It is its absence, not its presence, that prompts a closer look — and that look is for the conditions affecting how the midline develops.

That is a question for the obstetric or fetal medicine team who did the scan, and it is not one this page can answer. This page is about the adult finding, where the presence of a cavum is the normal variant and means nothing on its own. The two situations share a name and share nothing else.

What to ask, if anything

Is this the only finding? If the report describes a cavum and otherwise a normal study, that is the answer.
Is anything else described at the midline — enlarged ventricles, absent structures? Those would be separate sentences with their own weight.
Was I scanned for a symptom that is still unexplained? A normal variant does not explain a new problem, and the question stays open.

Frequently asked questions

Is a cavum septum pellucidum abnormal?: In an adult it is a normal anatomical variant. Everyone has one before birth; it usually closes in the first months of life and in some people it does not. Found on its own it needs no action.
Is it a cyst?: No. It is a fluid space between the two leaves of a thin membrane, not an enclosed sac with a wall of its own. Reports sometimes use the word cyst for an unusually large one, which is a description of size rather than a change of category.
Can it cause symptoms?: Not in the ordinary case. Very rarely a large cavum is described alongside signs that it is interfering with cerebrospinal fluid flow, and a report states that explicitly when it applies. Otherwise it is not the explanation for headaches or anything else.
My pregnancy scan mentioned the cavum septi pellucidi. Is that the same thing?: The same structure, the opposite question. On a fetal scan it should be present, and seeing it is a routine confirmation that the midline has formed normally; its absence is what prompts a closer look. That is a conversation for the team who performed the scan.
I have read it is linked to head injuries. Should I be worried?: A persistent cavum has been studied as a group-level marker in populations with repeated head impacts. A statistical association in a study population does not tell one person with an incidental finding anything about themselves, and it is not a reason for investigation on its own.

When you want a second read of the images themselves

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Words on this page

Each of these has its own page in the report glossary.

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Sources

Patient-facing procedure descriptions (MRI, CT, X-ray, ultrasound)RadiologyInfo.org — Radiological Society of North America & American College of Radiology
MRI scan — overview, how it is performed and resultsNHS (United Kingdom)
ACR Appropriateness Criteria and practice parameters for reportingAmerican College of Radiology

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Read Your Scan is informational only — not a medical diagnosis, and not a substitute for a licensed radiologist or your doctor. This page explains what a report says and what a radiologist looks at; it cannot tell you what your own images show. If you have urgent symptoms, seek care.