Cerebellar hemispheres

What it is

The cerebellar hemispheres are the two large lobes of the cerebellum, located on either side of the midline vermis. They play a major role in coordinating the movements of the limbs, and their lower portions include the cerebellar tonsils that descend in Chiari malformation type I.

Understanding Cerebellar hemispheres

Each cerebellar hemisphere helps coordinate movements on the same side of the body, contributing to smooth, accurate limb movements. The cerebellar tonsils — the structures that descend in Chiari I — are located at the lower, inner part of the hemispheres near the midline. Crowding or displacement of the hemispheres and tonsils can contribute to coordination difficulties (such as clumsiness or dysmetria) seen in some people with Chiari. Understanding the hemispheres helps clarify the structure of the cerebellum and where the tonsils sit within it. The hemispheres, vermis, and tonsils together make up the cerebellum involved in Chiari malformation.

Why it matters

Understanding the cerebellar hemispheres helps families see the structure of the cerebellum, where the descending tonsils are located, and why limb coordination can be affected in some people with Chiari.