Increased tissue motion found in individuals with Chiari malformation type I (CMI) may be the underlying cause of CMI symptoms. Patients may be treated with posterior fossa decompression (PFD) surgery with the goal of relieving brainstem compression by altering craniocervical morphology. Selection of PFD candidates is primarily determined based on subjective symptomatology. Therefore, a quantitative measure of surgical improvement may improve candidate selection for PFD surgery.
Displacement encoding with stimulated echoes (DENSE) MR phase images before and after surgery were used to quantify changes in displacement following surgery for 12 CMI patients (10 females, ages 38 ± 9) in a study approved by the institutional review board. An internally developed computer program was used to quantify tissue motion and strain in the cerebellum and brainstem. Spatially averaged values for each structure was used to determine significant changes in displacement and strain. Surgical outcome was determined using the Chicago Chiari Outcome Scale (CCOS).
Cerebellar mean peak displacement in the superior-inferior (SI) direction and anteriorposterior (AP) direction significantly decreased by 34% and 46%, respectively (p < 0.05). Mean peak displacement in the brainstem reduced by 24% in the SI direction (p < 0.05). Additionally, cerebellar compression and extension principle strain decreased by 21% and 28%, respectively (p < 0.05). A positive correlation was found between cerebellar and brainstem displacement in the SI direction before surgery with CCOS scores (r = 0.69, p < 0.05 and r = 0.66, p < 0.05).
Discussion and Conclusions
We observed that cerebellar and brainstem tissue motion and strains within the craniocervical region reduced following surgery. Additionally, we were able to establish a relationship between brain tissue mechanics and PFD surgical outcome. Our results suggest that patients with larger SI cerebellar and brainstem displacement prior to surgery may benefit from PFD surgical treatment.