Do patients with Chiari I Malformation and craniocervical instability present differently and have different outcomes? A comparison study

Introduction: Chiari malformation type 1 (CM1) is defined by the downward displacement of cerebellar tonsils below the foramen magnum, potentially causing brainstem compression or obstructing cerebrospinal fluid (CSF) flow. Our understanding of the relationship between CM1 and craniocervical instability (CCI) is limited, prompting this investigation.

Methods: Pediatric patients (0-18 years old) with surgically managed CM1 at our institution between 2010-2023 were retrospectively reviewed for demographic, clinical, radiographic, surgical, and follow-up data. The Chicago Chiari Outcome Scale (CCOS) was used to quantify treatment outcomes. CCI was defined as dynamic movement on flexion/extension study, Clival axial angle < 140, or basilar invagination on imaging.

Results: 225 patients with CM1 (117 male, 108 female) were included in the study, among whom 17/225 (8%) patients were diagnosed with CCI. At presentation, patients with CCI were more likely to present with irregular gait (p = 0.024) and cranial neuropathies (p = 0.012). Patients with CCI had greater tonsil herniation on initial MRI (mean = 14mm, IQR = 11-24mm) in comparison to patients without CCI (mean = 10mm, IQR = 8-14mm). 41% of patients with CCI had cranial cervical fusion to address the instability. After surgery, patients with CCI had a lower non-pain score (mean = 3.31; SD = 0.87) compared to patients without CCI (mean = 3.68; SD = 0.65). No significant difference was observed in the overall outcome score between the two groups. There were no significant differences in number of patients with syrinx or hydrocephalus between the two groups.

Conclusion : CM1 patients with CCI are more likely to present with irregular gait and cranial neuropathy, potentially secondary to nerve compression. Both cohorts had similar incidence of hydrocephalus and syringomyelia. Although patients with CCI were more likely to undergo cervical fusion, both groups had similar surgical outcomes.