Occipital bone

What it is

The occipital bone is the bone forming the back and base of the skull. It surrounds the foramen magnum (the opening where the brainstem meets the spinal cord), and a portion of it is removed during Chiari decompression surgery.

Understanding Occipital bone

The occipital bone houses the posterior fossa and forms the rim of the foramen magnum. Because the development of this bone influences the size of the posterior fossa, abnormalities in its formation are thought to contribute to the small or crowded posterior fossa seen in many people with Chiari I. During posterior fossa decompression surgery, surgeons remove a portion of the occipital bone (a suboccipital craniectomy) to enlarge the space at the back of the skull and relieve crowding at the foramen magnum. Understanding the occipital bone clarifies both a developmental factor in Chiari (how the skull base forms) and the bone that surgery modifies to create more room.

Why it matters

Understanding the occipital bone helps families see how skull-base development relates to the crowded posterior fossa in Chiari, and which bone surgeons remove part of to create more space.