What it is
Chiari malformation (most commonly Chiari I) is a structural variation where the bottom of the cerebellum — the part called the cerebellar tonsils — extends below the base of the skull into the upper spinal canal. Many people with this finding have no symptoms at all; the malformation is often discovered incidentally on imaging ordered for something else.
When it does cause symptoms, the classic pattern is a headache at the back of the head triggered by coughing, straining, or exertion, sometimes with neck pain, hand symptoms, or balance changes. A related finding called syringomyelia — a fluid-filled cavity within the spinal cord — can develop in some patients and change the clinical picture.
How we approach it
Not every Chiari finding needs surgery. In fact, most don't. The evaluation focuses on whether the symptoms match the anatomy, whether there's a syrinx, and whether the pattern of symptoms is progressive or stable. We use MRI of the brain and full spine, sometimes with specialized flow studies.
When surgery is considered
Surgery — typically a posterior fossa decompression — is considered when symptoms clearly match the anatomy and are affecting quality of life, or when a syrinx is present and progressive. The goal of decompression is to restore normal cerebrospinal fluid flow at the skull base; it's not a cosmetic fix for an incidental MRI finding.