Relationship between the geometric characteristics of the craniocervical junction and the persistence of postoperative symptoms in patients with Arnold–Chiari malformation type I

Background: Chiari malformation type I (CM-I) is characterized by cerebellar tonsillar herniation through the foramen magnum and is frequently associated with abnormalities of the posterior fossa (PF) and craniovertebral junction (CVJ). Although tonsillar descent remains a key diagnostic criterion, treatment decisions rely on the integration of clinical symptoms and radiological findings. Morphometric assessment of PF geometry, including the Raybaud pentagon, may provide a more objective characterization of craniovertebral anatomy and help identify anatomical patterns associated with postoperative symptom persistence. According to the Raybaud method, patients can be classified into divergent and superimposed geometric patterns based on the relationship between the reference lines defining the PF and CVJ morphology. Methods: An observational, analytical, retrospective study was carried out in the department of neurosurgery of a tertiary referral hospital. The study included patients diagnosed with CM-I who underwent surgical treatment. All patients underwent the same standardized surgical procedure consisting of PF decompression with C1 posterior arch resection, without duraplasty or tonsillopexy. The relationship between the geometric characteristics of the PF and CVJ and the persistence of symptoms after surgery was subsequently evaluated. Results: Seventy medical records were reviewed, of which 64 met the inclusion criteria and were included in the final statistical analysis. Patients classified within the divergent geometric pattern showed a lower likelihood of persistent postoperative symptoms than those with the superimposed pattern. A statistically significant association was identified between CVJ geometry and the persistence of postoperative symptoms. Conclusion: A statistically significant association was observed between the geometric pattern of the CVJ and the persistence of postoperative symptoms. Specifically, patients with a divergent pattern showed a lower likelihood of persistent symptoms than those with a superimposed pattern. These findings suggest that Raybaud morphometric classification may provide useful prognostic information regarding postoperative clinical outcomes in patients with CM-I.