Brainstem

What it is

The brainstem is the lower part of the brain that connects the cerebrum and cerebellum to the spinal cord. It controls many vital functions — including breathing, heart rate, blood pressure, and swallowing — and carries signals between the brain and body. It is displaced downward in the more severe Chiari malformations.

Understanding Brainstem

Composed of the midbrain, pons, and medulla, the brainstem passes through the foramen magnum to become the spinal cord. In Chiari malformation type I, the brainstem is generally not displaced, but in type II and the Chiari 1.5 variant, parts of the brainstem (such as the medulla and its obex) extend downward through the foramen magnum. Because the brainstem controls vital functions, its compression or displacement can cause serious symptoms — such as breathing difficulties, swallowing problems, and lower cranial nerve dysfunction — which is why brainstem involvement marks the more severe forms. Understanding the brainstem clarifies why types II and 1.5 are more serious than type I.

Why it matters

Understanding the brainstem helps families see why Chiari types that involve it (II and 1.5) are more serious — because the brainstem controls vital functions — and why breathing or swallowing symptoms warrant urgent attention.