Prevalence of idiopathic cuneate gyrus herniation based on emergency room CT examinations.

Idiopathic brain herniation caused by a focal dural defect can be confused for a mass or post-traumatic herniation. The prevalence of idiopathic brain herniation has never been described. We sought to ascertain the prevalence of idiopathic cuneate gyrus herniation in a general emergency room (ER) population on computed tomography (CT) imaging. The purpose of this study is to elucidate cuneate gyrus herniation and differentiate it from other pathologic conditions such as mass or traumatic herniation and to provide its anatomical prevalence in an ER population. Consecutive emergency room CT scans of the brain were evaluated prospectively for cuneate gyrus herniation over a 1 year period by a neuroradiologist. Of 1,500 brain CT scans evaluated, 11 patients demonstrated idiopathic cuneus gyrus herniation. The prevalence was 0.73 %. CT manifestations are normal brain tissue herniating into the superior cerebellar cistern. Idiopathic brain herniation can be mistaken for a pathologic process. We found the prevalence of one such idiopathic brain herniation, involving the cuneus gyrus, to be exceedingly rare. CT imaging demonstrates normal brain tissue herniating beyond the dural boundary.