Klippel-Feil syndrome, iniencephalus, anencephalus, hindbrain hernia and mirror movements: overdistention of the neural tube.

Bony anomalies encountered in the 'no neck' form of Klippel-Feil syndrome (KFS) are a wide, short, fused, bifid, retroflexed spinal canal; craniolacunia, cranium bifidum, and acrania. The only symptom may be mirror movement (MM). The CNS anomalies are hindbrain hernia, hydrocephalus, hydromyelia, syringomyelia, meningocele, myelocele, encephalocele, and anencephalus. In severe KFS, i.e. iniencephalus (IN) and in anencephalus (AN), the inion is in contact with the back. In both there is hindbrain hernia and the left thorax may contain the stomach tethered to an anterior spina bifida. KFS results from distortion of somites by an overdistended neural tube. A neural tube that fails to close cannot overdistend.