THE ONE BONE SPINE - A FAILURE OF NOTOCHORD SCLEROTOME SIGNALING/

Three cases of extensive vertebral fusions with absent clivo-axial ang le are presented. The 'bone-within-bone' appearance in two patients wi th almost complete fusion of the spine suggested ossification of the n otochord and perinotochordal sheath. On the basis of the radiological appearances and the results of recent molecular genetic studies on ver tebrate embryos, the suggested time of segmentation failure along the axis of the craniovertebral junction and between vertebrae is the thir d to fifth week of gestation. The possible roles of the Pax-1 gene and of signalling between notochord and sclerotome are discussed, conclud ing that an early defect of the notochord may be responsible for this type of failure of segmentation. Indications for surgery in these case s included cord compression with brachialgia and 'chin-on-chest' defor mity causing severely restricted visual fields. A critical review of c linical lessons learned in the operative treatment is presented.