A new pathogenetic explanation of human chiari malformations.

804 Chiari malformations are a heterogeneous group of congenital disorders that are defined by anatomic anomalies of the cerebellum, brainstem, and craniocervical junction, with downward displacement of the cerebellum, either alone or together with the lower medulla, into the spinal canal. 1 The major categories of symptoms of Chiari malformations are those related to obstructive hydrocephalus, abnormal eye movements, cerebellar deficits, and spinal myelomeningocele. 1 Patients with Chiari malformations are spared the latter, as they do not have neural tube defects such as a myelomeningocele. The pathogenesis of congenital Chiari malformations remains the subject of debate. Multiple theories have been proposed, though none explains all the features. The molecular genetic theory postulates that Chiari malformations result from primary defects in the genetic programming of hindbrain segmentation and of growth of associated bone and cranial structures. 2 The hydrodynamic pulsion theory suggests that early progressive foetal hydrocephalus pushes down on the brainstem and cerebellum. 3 And the oligocerebrospinal fluid theory proposes that defective closure of the neural tube in early foetal development results in leakage of cerebrospinal fluid, and thus insufficient cerebrospinal volume to fully distend the embryonic ventricular system, which leads to a small posterior fossa and cerebral disorganization. 4 The pathogenesis of Chiari malformations has always been the subject of debate. However, one of the interesting things is that we have never heard that any animals of Subphylum Vertebrata once suffered from Chiari malformation and there is indeed no literature reporting that. We cannot help wondering such disturbing problems: What are on earth the unique features of human that make us have frustration with Chiari malformations? Let's shift our sights back to the abnormal anatomic features of Chiari malformation. In most cases, the posterior fossa is small, and neural elements are crowded and impacted at the foramen magnum. 1 There was a time when lots of scholars acknowledging the crowding theory which postulated that restricted growth of the posterior fossa causes compression of neural tissue, which is then squeezed through the foramen magnum like toothpaste through a tube. 5 In support of this theory, the posterior fossa is abnormally small and the torcula is displaced downward in patients with Chiari malformations. 6 This is a kind of naive materialism and simple and dialectical view on the pathological theory of Chiari malformation. Nevertheless, this point of view is yet the closest one to the essence of our hypothesis. Scientists claim …