Mesencephalic spur (beaking deformity of the tectum) in Arnold-Chiari malformation.

The beaking deformity of the tectum, referred to in this paper as the mesencephalic spur, is regularly present in the Type II variety of the Arnold-Chiari malformation in varying degrees of severity. When the mesencephalic spur is related to associated myelomeningocele, it was found that the more extensive the myelomeningocele, and the older the affected children, the more prominent was the mesencephalic spur.