A form of spinal dysraphism associated with a protruding cyst made up of either meninges (i.e., a meningocele) or meninges in combination with spinal cord tissue (i.e., a meningomyelocele). These lesions are frequently associated with spinal cord dysfunction, hydrocephalus, and syringomyelia. (From Davis et al., Textbook of Neuropathology, 2nd ed, pp224-5)