MATERIAL and METHODS: The radiological and demographic data from 251 patients with CM-1 followed in our clinic between 2014 and 2019 were compared with data from 273 persons in a healthy control group. Fourth ventricle dimensions, amount of cerebellar tonsillar herniation, and tentorium twinning angle were measured. Statistical analysis was performed.

RESULTS: The mean tentorial twinning angle, craniocaudal length, and anteroposterior length of the fourth ventricle were significantly greater than the mean of the same measurements in the healthy control group. In addition, in a subgroup analysis conducted according to treatment modalities of patients with CM-1, the length between the bilateral recesses of the fourth ventricle was found to be statistically significantly greater in the subgroup of patients who underwent surgery compared with those in the nonsurgical subgroup.

CONCLUSION: Fourth ventricle enlargement is a radiographic finding in patients with CM-1. Studies evaluating clinical presentation, severity, and outcome after treatment will be useful in revealing the importance of this entity. Keywords : Cerebellum, Fourth ventricle, Tonsillar herniation, Tentorium, Posterior fossa