Meningocele manqué refers to an element of dorsal tethering bands composed of fibrotic or atretic neural tissue connecting the spinal cord to dura or surrounding structures. They are usually found incidentally during surgical exploration for other elements. *from Medscape Article on TCS & OSD
It is a form of spinal dysraphism where nerve roots and fibrous bands tether normal neural structures. This is exactly what Kennedy had going on. She had nerves and fibrous bands attaching to her spinal cord which was stretching and pulling it.