Sectioning of the Filum Terminale in Patients with Chiari Malformation Type 1 Associated with Occult Tethered Cord Syndrome: Literature Review

Abstract Approximately 125 years ago, a group of pathologies now known as Chiari malformations was described for the first time. However, some mechanisms of its formation still remain unknown. A bibliographic survey was performed through a search in PubMed. In 1938, it was already theorized that an increase in spinal cord tension could be the cause of Chiari malformation type 1 (CM1) tonsillar herniation. In 1953, a condition known for the anchoring of the filum terminale to the vertebral canal was described for the first time and would later be known as tethered cord syndrome (TCS). Some studies have shown that it is associated with increased tension in the spinal cord, and this formed the basis for a possible pathophysiological explanation of tonsillar herniation. Case series emerged reporting that treatment for TCS with the sectioning of the filum terminale (SFT) could provide clinical improvement of patients with CM1. A new pathological entity emerged when it was realized that patients with the clinical picture of TCS could have the medullary cone in its normal position, differing from the caudal migration expected for the TCS. This condition became known as occult tethered cord syndrome (OTCS). Case series attempted to demonstrate its association with the origin of CM1, a non-intuitive association, since the cone in the normal position contradicts traction as a source of tonsillar herniation. To this day, the absence of randomized control trials limits any conclusions regarding the effectiveness of SFT for the treatment of patients with CM1.