Diffusion-weighted magnetic resonance imaging in a case of Kernohan's notch phenomenon

Abstract

Dear Editor, Kernohan's notch phenomenon is characterized by false localizing motor signs caused by compression of the cerebral peduncle against the tentorial edge, contralateral to a supratentorial mass [3]. Using magnetic resonance imaging (MRI), several cases of this phenomenon due to traumatic acute subdural hematomas were reported. A case of Kernohan's notch phenomenon with diffusionweighted (DW) MRI in a chronic stage was reported before [5]. We present a case of Kernohan's notch phenomenon secondary to a traumatic acute subdural hematoma where MRI, mainly DW images, showed visibly abnormal findings in the early subacute stage. A 19-year-old male felt nauseous after boxing. Soon afterwards he became unconscious following which he was transferred to a local hospital. After being diagnosed with an acute subdural hematoma (Fig. 1a), he was intubated and transferred to our hospital. In the emergency room his Glasgow Coma Scale score was 7. He was able to move his right extremities but his left extremities exhibited an extended posture. Light reflex of the left pupil was sluggish. Babinski signs were negative bilaterally. Subsequently, a left craniotomy was performed with evacuation of the subdural hematoma 6 h after the onset. Postoperatively, his pupillary reaction normalized. He began to regain consciousness and gradually the right motor function improved; however, the left hemiplegia persisted. After 21 days, the patient had persistent left hemiparesis and was transferred to another hospital for rehabilitation. MRI (1.5 T Philips Intera) performed 7 days after the operation revealed that the subdural hematoma was successfully evacuated. However, T2-weighted MRI revealed a lesion in the right cerebral peduncle (Fig. 1b, c). Furthermore, DW imaging (EPI Matrix 256×256, FOV=230 mm, TR/TE=2721/72 ms, b=1,000 mm/s, thickness=5 mm) revealed the lesion to be hyperintense (Fig. 1d). The apparent diffusion coefficient (ADC) map showed the area as a low signal (Fig. 1e), and it had a relatively low ADC value (0.78×10 mm/s) compared to that of the contralateral cerebral peduncle (0.90×10 mm/s). Besides conventional MRI, Binder et al. first reported Kernohan's notch phenomenon with transcranial magnetic stimulation [2]. Later Yoo et al. reported a case of Kernohan's notch phenomenon with diffusion tensor imaging, which is the only published case where DW imaging was used [5], here, MRI was performed 6 weeks after the onset, fraction anisotropy (FA) and ADC values were shown but DW image was not included. The FA value decreased in the affected cerebral peduncle, but a marked difference was not seen between ADC values on the contralateral side or in the control subjects. Marmarou, Barzo et al. conducted clinical and experimental studies on traumatized brains. They reported that increased intracellular water volume and reduced ADC value indicates cytotoxic edema. During the subacute stage, axonal injury causes a reduced ADC value after traumatic S. Uesugi (*) Department of Neurosurgery, Kanmon Medical Center, 1-1 Sotouracho, Chofu, Shimonoseki, Yamaguchi 7520985, Japan e-mail: uesugis@simonoseki2.hosp.go.jp