A Puzzling Exam: Kernohan’s Notch Reimaged

Abstract

•We provide a visual image of the consequeces of massive brainstem shift with oculomotor and peduncle injury.•Acute space occupying lesions may cause ipsilateral hemiparesis – and can be a false localizing sign. Conventional teaching on the neurologic examination suggests findings can be attributed to specific regions – which improves timely diagnosis and treatment, particularly in life threatening situations. Rarely, puzzling patient presentations can wrongly lead to false localization. A 36-year-old man was found comatose. Head CT demonstrated an acute right convexity subdural hematoma, causing a nearly 2 cm midline shift. Initial neurologic examination was confounded by paralytic agents; however, there was a dilated-light fixed right pupil. The patient was taken for a right hemicraniectomy and hematoma evacuation (Fig. 1). Post-operative examination demonstrated right-sided oculomotor palsy and hemiplegia with preserved left-sided strength—consistent with a false localizing sign. An MRI on POD#1 revealed abnormal T2-signal hyperintensity involving the left anterolateral midbrain and cerebral peduncle, indicative of compression of the contralateral crus cerebri against the contralateral tentorial incisura (“notch”). The descending corticospinal tracts travel from the motor cortex through the ipsilateral crus cerebri into the inferior brainstem where they decussate-transmitting motor stimuli to the contralateral hemibody. Correspondingly, right-sided lesions above the decussation produce left-sided deficits. In the present case, the expected deficits would have been in the left hemibody. However, in rare circumstances involving a significant midline shift the contralateral peduncle is injured via compression at the tentorium. The oculomotor at the same side of the hematoma is as expected and either caused by strech of the nerve or direct compression of the uncus. This false localizing sign has been honored by the eponym "Kernohans Notch"..[[1]Kernohan J.W. Woltman H.W. Incisura of the crus due to contralateral brain tumor.Arch NeurPsych. 1929; 21: 274-287https://doi.org/10.1001/archneurpsyc.1929.02210200030004Crossref Scopus (117) Google Scholar] More deserving of the distinction is Groeneveld [[2]Dammers R Volovci V and Kompanje EJOThe History of the Kernohan Notch Revisited.Neurosurgery. 2016; 78: 581-584https://doi.org/10.1227/NEU.0000000000001097Crossref PubMed Scopus (0) Google Scholar] and Schaltenbrand who explained the injury as a knife-like stab (“Messerähnlichen Wirkung”) from the tentorium and possibly petrosal bone. There is a fascination with the Kernohan's notch phenomenon as evidenced by an ongoing flurry of case reports in the literature. Our patient clearly visualizes what has previously only been described in text and provides better proof of its existance. Picture Quiz: A 36 year-old male found down is noted on neurologic examination to have right hemiplegia and right oculomotor nerve palsy, with intact left upper and lower extremity function. Based on the exam, what is the most likely level of the lesion? A. Left motor cortex B. Right basal ganglia C. Left cerebral peduncle D. Right upper medulla Answer on page 336. LPC, AP, RCP, PCR, JLF, and EFW all provided substantial direct medical or surgical care pertaining to the diagnosis and treatment of the patient; LPC, AP, and CSG gathered the data and wrote manuscript/created the figure, PJR obtained formal patient consent and edited the manuscript, JLF and EFW supervised the project and made final manuscript editorial edits and approvals. None. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. A Puzzling Exam: Kernohan’s Notch ReimagedJournal of Clinical NeuroscienceVol. 80PreviewThe Answer is: C. Left cerebral peduncle. Full-Text PDF