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• Kernohan Notch, Retractor Crunch, or Interhemispheric Diaschisis:
  Iraj Derakhshan
  Published on: 19 November 2008

• Published on: 19 November 2008

  Kernohan Notch, Retractor Crunch, or Interhemispheric Diaschisis:

  • Iraj Derakhshan, Neurologist

  Dear Editor,

  I read the article of Yoo et al [1] in the Journal with interest and would like to offer another explanation as to the cause of delayed and weaker response of the right ABP to transcranial magnetic stimulation of the right hemisphere, i.e. interhemispheric diaschisis.

  Firstly, there is substantial number of case reports documenting ipsilateral paralysis in unilateral cranial lesions (e.g....

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  Dear Editor,

  I read the article of Yoo et al [1] in the Journal with interest and would like to offer another explanation as to the cause of delayed and weaker response of the right ABP to transcranial magnetic stimulation of the right hemisphere, i.e. interhemispheric diaschisis.

  Firstly, there is substantial number of case reports documenting ipsilateral paralysis in unilateral cranial lesions (e.g. subdural hematomas) in the absence of any cerebral herniation [2, 3]. Second, the cases described by Kernohan and Woltman were all involving the left hemisphere [4], a finding that requires a physiological explanation not afforded by the notch created by horizontal shifting of the midbrain in such cases [1]. Third, laterality related (left-sided) weakness has been described with callosotomies performed without the use of a retractor causing injury to the right hemisphere (as an explanation of such events) [5]. Lastly, earlier onset of activity in the hemisphere containing the command center (left in vast majority of people) has been documented repeatedly; most recently by Wisneski et al [6], indicating transcallosal transfer of motor commands arising from the major hemisphere for movements occurring in the nondominant side of the body; i.e. commands that are implemented by the minor hemisphere [7].

  In short, these observations suggest that the hemiparesis described by Yoo et al was based on diaschitic injury (deafferentation) of the minor hemisphere (in this case the left) in a patient wired as a left hander (but ostensibly right handed) and that the Kernohan notch they described was an irrelevant artifact. As described elsewhere, such cases are the neural substrates of crossed aphasias and crossed nonaphasias [2].

  REFERENCES

  1. Yoo WK, Kim DS, Kwon YH, Jang SH.
  Kernohan's notch phenomenon demonstrated by diffusion tensor imaging and transcranial magnetic stimulation.
  J Neurol Neurosurg Psychiatry. 2008; 79:1295-1297.

  2. Derakhshan I.
  Callosum and movement control: case reports.
  Neurol Res. 2003; 25:538-542.

  3. Kersey RD.
  Acute Subdural Hematoma after a Reported Mild Concussion: A Case Report.
  J Athl Train. 1998; 33:264-268.

  4. Peyser E, Doron Y.
  Ipsilateral hemiplegia in supratentorial space occupying lesions.
  Int Surg. 1966; 45:689-695.

  5. Phillips J, Sakas DE.
  Anterior callosotomy for intractable epilepsy: outcome in a series of twenty patients.
  Br J Neurosurg. 1996; 10:351-356.

  6. Wisneski KJ, Anderson N, Schalk G, Smyth M, Moran D, Leuthardt EC.
  Unique Cortical Physiology Associated With Ipsilateral Hand Movements and Neuroprosthetic Implications.
  Stroke. October 2008.

  7. Derakhshan I.
  Laterality of motor control revisited: directionality of callosal traffic and its rehabilitative implications.
  Top Stroke Rehabil. 2005; 12:76-82.

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  Conflict of Interest:
  None declared.

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