Chiari malformation: Meaning in a Radiology Report

Also written as: Chiari I malformation, tonsillar ectopia, low-lying cerebellar tonsils

A Chiari malformation means the lowest part of the cerebellum, at the back of the brain, extends down through the opening at the base of the skull.

What it means

The cerebellum sits at the back of the brain, just above the large opening where the skull meets the spine. Its lowest parts are called the tonsils, which have nothing to do with the tonsils in the throat. In a Chiari I malformation, they extend 5 mm or more below this opening. This can crowd the space and slow the flow of brain fluid. It is often present from birth.

When it matters

Small descents of a few millimeters are common and often called tonsillar ectopia. Many people with a Chiari malformation never have symptoms. Next steps depend on symptoms, such as headaches at the back of the head brought on by coughing or straining. They also depend on whether a fluid-filled cavity has formed in the spinal cord (a syrinx). Your doctor may suggest a spine MRI or a specialist review.

Questions to ask your doctor

How far below the skull opening do the tonsils extend?
Is there a syrinx, or any sign of blocked fluid flow?
Are my symptoms typical of a Chiari malformation, or likely unrelated?

General information, not medical advice. What a finding means for you depends on your symptoms, your history and the images themselves, so talk your results through with a doctor.