Venous outflow impairment in the posterior Cerebellum: A new pathogenic perspective on Chiari Malformation type I

• Chiari Malformation Type 1 is the prolapse of cerebellar tonsils into the cervical canal. Its etiology remains unclear. • The venous system at the craniovertebral junction plays a pivotal role in intracranial fluid distribution. • Several neurological pathologies are associated with increased venous outflow resistance from the craniospinal complex. • CM1 may result from regional edema caused by impaired venous drainage through the posterior venous complex. Chiari Malformation type 1 is defined as the prolapse of the cerebellar tonsils downward into the cervical canal. Known since the late 19th century, it has always lacked a clear etiological explanation and an evidence-based treatment. The comprehension of brain physiology and anatomy has evolved increasingly fast with contributions from different fields of science. Particularly, cerebrospinal fluid functions and movements, along with the venous contribution to neural physiology, are emerging concepts that are providing new insights into pathologies not yet fully described or understood. We propose a new pathogenic theory for Chiari Malformation type 1, based on the latest concepts of cerebrovascular physiology. Cerebellar tonsil herniation could result from regional edema caused by an impairment in venous drainage through the posterior paravertebral venous complex. This could provide an explanation with Goel’s report about atlantoaxial instability as the cause of tonsillar prolapse and is consistent both for cases with a small posterior fossa and for cases that don’t fit that classical definition. Further studies are needed to better assess the internal and external validity of this theory.