[Magnetic resonance imaging of Kernohan's notch in chronic subdural hematoma]

Compression of the crus cerebri against the free edge of the tentorium contralateral to a supratentorial mass, the so-called Kernohan's notch, can be a cause of false localizing sign. Kernohan's notch has been thoroughly studied clinically and pathologically, but not radiographically. The authors describe a case of left chronic subdural hematoma, which resulted in left hemiparesis caused by Kernohan's notch. Injury to the contralateral cerebral peduncle was clearly shown by magnetic resonance imaging (MRI) performed in the postoperative period. A 43-year-old man was transferred to our hospital in deep coma with dilated pupils, unreactive to light. Computed tomography (CT) scans obtained on admission revealed a left chronic subdural hematoma and a midline shift to the right. After drainage and irrigation of the left chronic subdural hematoma through a single burr hole, his clinical condition improved gradually. But 1 month after the operation, mild left hemiparesis still persisted. MRI T2-weighted images demonstrated an abnormally increased signal area in the right cerebral peduncle. T1-weighted coronal images showed the anatomical relationship between the hypointense lesion in the right cerebral peduncle and tentorial edge. Three-dimensional-MRI (3D-MRI) clearly demonstrated the surface image of Kernohan's notch. We emphasize the utility of 3D-MRI for detecting evidence of brain stem injury, such as Kerno han's notch.