[The posterior cranium and its dysmorphisms].

The deformation of the posterior part of the skull (occipito-vertebral region) induced directly, occurs in numerous pathological situations. Its significance is frequently overlooked. Lesions of the cranial content, alterations of the lambdoid suture or other premature synostosis, abnormal constraint related to posture or to muscular activity can modify the posterior curvature of the skull, generally flattening it. The authors propose a classification based on three points: intracranial pathology, bone pathology and extrinsic pathology. Concerning intracranial pathology, alterations of the brain or CSF fluid can induce either insufficient (microencephaly) or excessive (hydrocephalus, Dandy Walker or Arnold Chiari malformations) expansion. Concerning bone pathology, sagittal synostosis (scaphocephaly) induces a bulging and coronal synostosis a flatness of the posterior skull. Bilateral premature lambdoid synostosis (pachycephaly) produces total flatness of the back of the skull. Concerning extrinsic pathology, dysmorphism is often asymmetrical and results from extracranial mechanical application dysfunction such as inborn torticollis, cervical spine pathology (Klippel-Feil syndrome), or prolonged decubitus during the first year of life. The different surgical procedures are described and the authors describe a personal technique for correcting this dysmorphism: the turned biparietal flap transposition. The back of the skull is remodelled (either asymmetrical or bilateral flatness), and patients with no need for a helmet can lie on their backs immediately after the operation.