CSF leak

What it means

Cerebrospinal fluid (CSF) is the clear fluid that surrounds and cushions the brain and spinal cord, contained within a tough membrane called the dura. A CSF leak happens when there is a tear or opening in this membrane, allowing fluid to escape into surrounding tissues instead of staying within its normal space. This lowers the pressure and volume of fluid supporting the brain, which produces the leak's most characteristic symptom: a headache that is markedly worse when upright and improves when lying flat.

Leaks can occur in the spine, most often after spine surgery or a lumbar puncture (spinal tap), or in the skull base, sometimes following head trauma, sinus surgery, or occurring spontaneously.

Why it appears on a CT or MRI report

CSF leaks are looked for using MRI, CT myelography (CT taken after contrast dye is injected into the spinal fluid), or specialised nuclear medicine studies, particularly after spine surgery when a leak is suspected clinically. Reports may describe a fluid collection outside the dura (an extradural fluid collection), a defect in the dural membrane itself, or, on myelography, contrast dye leaking out of the expected fluid-filled space. Sometimes imaging is done specifically to find the exact level of a leak before it is surgically repaired, and the report will pinpoint the spinal level or skull-base location involved.

What it usually means

The most common setting for a CSF leak is after spine surgery, where the dura can be nicked or fail to seal completely — a well-recognised, generally manageable complication rather than a sign of a botched procedure. Leaks can also follow a diagnostic spinal tap or epidural, or occur spontaneously in people with an underlying connective tissue weakness or a small tear from something as minor as a strong cough. The main risks of an ongoing leak are the disabling positional headache and, less commonly, infection (meningitis) if the opening lets bacteria in, since it forms a direct connection between the outside and the fluid space around the brain and spinal cord. Because of this infection risk, a suspected or confirmed leak is generally treated as something to actively address rather than watch indefinitely.

When to follow up

If your report describes a CSF leak, especially after recent spine surgery, contact your surgical team promptly — many leaks are managed with a period of flat bed rest, and persistent ones are treated with a targeted procedure called an epidural blood patch, which uses your own blood to seal the opening; larger or non-healing leaks sometimes need surgical repair. Seek urgent medical attention for a severe positional headache accompanied by fever, neck stiffness, confusion, or fluid draining from the nose, ear, or a surgical wound, as these can indicate infection and should not wait.

A plain-language way to picture it

Picture the brain and spinal cord floating in a sealed, fluid-filled bag, the way a fragile item is cushioned in a bag of water inside a shipping box. A CSF leak is a small puncture in that bag: fluid slowly seeps out, the cushioning drops, and the contents settle lower when you stand up — which is why the headache eases when you lie flat. Sealing the puncture, whether the body does it on its own with rest or a doctor helps it along with a blood patch or stitch, is what stops the fluid loss and resolves the headache.