Tethering of the conus medullaris within the sacrum.

Included among various forms of craniovertebral congenital defects, known generally as spinal dysraphism or myelodysplasia, is a little described condition produced by the conus medullaris being tethered within the confines of the sacrum, usually by a lipomatous growth. Diagnosis may be difficult and is often not considered by clinicians in spite of characteristic clinical and radiographic appearances. Previous writers on anomalies of the central nervous system have seldom considered this entity separately although treatment differs from that in all other lumbosacral myelodysplasias. Three successive cases are now presented, the relevant embryological and clinical literature is reviewed, and emphasis is placed on positive contrast diagnosis and proper definitive therapy.