Locked-in Syndrome Due to Transtentorial Herniation and Kernohan Notch Phenomenon
Diffusion tensor imaging data were acquired at 3 months after onset using a 6-channel head coil on 1.5 T. Analyses of the corticospinal tract (CST) and corticoreticulospinal tract (CRT) were performed by selection of fibers passing through 2 regions of interest (ROIs), respectively. Regions of interest were as follows: CST (the first ROI: portion of anterior blue at the lower pons; and the second ROI: portion of anterior blue at the upper pons on the axial image of the color map), CRT (the first ROI: the reticular formation of the medulla; and the second ROI: the tegmentum of the midbrain on the axial image of the b0 map). The termination criteria used for fiber tracking were FA < 0.15, angle < 27 degrees. On 3-month diffusion tensor tractography (DTT), both CSTs and CRTs were discontinued at the brainstem level (the right CST: midbrain level; the left CST: lower pons level; and both CRTs: midbrain level) (Fig. 1C). Our results on DTT presented severe injuries of both CSTs and CRTs.
Transtentorial herniation is characterized by downward displacement of medial brain structures out of the cranium through the tentorial notch, caused by increased intracranial pressure,1 whereas Kernohan notch phenomenon is defined as ipsilateral hemiplegia caused by compression of the contralateral cerebral peduncle against the tentorial edge by a supratentorial mass.2 Locked-in syndrome is a neurological condition in which a patient is aware and awake but cannot move owing to quadriplegia.3,4 In this study, both CSTs and CRTs were discontinued at the brainstem level on 3-month DTT. The injury of the right CST and CRT appeared to be caused by transtentorial herniation, and the injury of the left CST and CRT seemed to be caused by Kernohan notch phenomenon.