Morphometric MRI Changes After Posterior Fossa Decompression in Chiari Type I Malformation

Objective: Chiari type I malformation (CM1) involves herniation of the cerebellar tonsils through the foramen magnum and altered cerebrospinal fluid (CSF) dynamics.Morphometric magnetic resonance imaging (MRI) measurements can objectively assess anatomical and physiological changes after posterior fossa decompression surgery (PFDS).This study evaluated postoperative morphometric alterations in CM1 and their implications for CSF flow.Method: This retrospective study included 23 adult patients who underwent PFDS for CM1 between 2015 and 2024.Preoperative and postoperative mid-sagittal MRI images were analyzed to measure tonsillar ectopia (TE), displacement of the iter (DOI), and mammillopontine distance (MPD).Boogard's angle (BooA) was used as an anatomical reference for postoperative evaluation.Paired t-tests were used for comparison of morphometric parameters, with p<0.05 considered statistically significant. Results:The mean age of patients was 34.08.7 years; 19 (82.6%) were female.The mean TE significantly decreased from 10.92.8 mm preoperatively to 6.92.5 mm postoperatively (p=0.0003).DOI also showed a significant reduction from 4.20.9mm to 3.90.8mm (p=0.048).No significant change was observed in MPD (6.20.7 mm vs. 6.10.7 mm, p=0.324). Conclusion: PFDS effectively reduces tonsillar descent in CM1, confirming the anatomical decompression of the posterior fossa.The modest reduction in DOI suggests potential improvement in CSF flow, while stable MPD values indicate limited brainstem displacement.Larger prospective studies incorporating dynamic CSF