To the Editor:
As a clinical neurologist with interest in laterality of motor control, I read the review by Leffert and Schwamm1
regarding neuroaxial anesthesia in parturients with intracranial pathology. They emphasized the role of transtentorial and lateral shifts of the brain in the management of those patients harboring space-occupying lesions. However, as shown in the hitherto neglected figure 7 of the classical article by Kernohan and Woltman,2
only half of the patients with supratentorial lesions (35 patients total) developed the ominous pyramidal signs ipsilateral to the tumor, whereas all of them showed notching of the contralateral cerebral peduncle (i.e.
, only 17 of 35 had ipsilateral pyramidal signs). Clearly, therefore, transtentorial herniation must be discounted as the physiological underpinning for the emergence of those classically described pyramidal signs; the harbinger of “herniation.”3–5
Instead, according to the new insight, occurrence of interhemispheric diaschisis provides the proper explanation for the emergence of the pyramidal signs ipsilateral to the major hemisphere (harboring the lesion). As to the authors’ references to lateral shifting of supratentorial contents, it does not fair any better than the transtentorial displacement alternative in explicating the semiology, given the recent insights to the laterality of consciousness and breathing.3–7
Thus, motor control (i.e.
, the command center for movements regardless of the laterality of the effectors involved) resides in the hemisphere which handles respiration and speech at the same time.4–7
One manifestation of this sharing of resources is that speech occurs exclusively as we exhale.
Another is the fact that speeches and nonverbal tasks interrupt the performance of the dominant hand more than the nondominant hand, also indicating sharing of resources.8
Turning to the laterality-indexed symptoms in clinical neurology and similar to the data provided by Kernohan and Woltman, the incidence of epilepsy in lesions distributed equally between the two hemispheres does not exceed 50%. This signifies that only one of the two hemispheres is capable of generating seizures.10
Finally, bimanual simultaneous drawing always results in a longer and straighter line drawn by the hand opposite to the major hemisphere (the hemisphere of action) because the nondominant hand falls behind the dominant by an interhemispheric transfer time. The dominant hand, therefore, moves faster than the nondominant if one swings his or her arms from side to side, manifested by a wider distance between the fists as one moves the arms to his or her neurally dominant side.12
In the same vein, earlier activation and wider excursion of the right diaphragm while breathing have been documented using dynamic magnetic resonance imaging.7
Clinically, lack of a relationship between lateral displacement of the brain (i.e.
, midline shift) and development of coma has been noted in a prospective study involving emergency room referrals in a metropolitan area.13
Interestingly, the study conducted by Melo et al.
revealed a left to right hemispheric ratio of 7:2 for an ischemic infarction causing coma (among the nine patients studied). This ratio is very similar to that which has seen reported in a reaction time study of lexical decision making conducted by Hamer and Lambert14
where 12 of the 15 right-handed bilingual adults responded faster to stimuli arising in the right visual field with the remainder performing faster in the opposite direction. In conclusion, it is the laterality of the lesion as it relates to the neural handedness of the subject that determines the fate of the patient in the circumstances detailed by the authors, affecting their ability to breathe spontaneously.
Given the above data, a patient’s Glasgow Coma Scale should be the determining factor in the outcome in these patients as the latter is heavily biased toward the integrity of the major hemisphere wherein the command center lies.
The author dedicates this work to the tender memories of his beloved sister Farkhondeh Derakhshan (died in exile).
The author declares no competing interests.
Iraj Derakhshan, M.D.
, Raleigh General Hospital, Charleston, West Virginia.email@example.com
1. Leffert LR, Schwamm LH. Neuraxial anesthesia in parturients with intracranial pathology: A comprehensive review and reassessment of risk. ANESTHESIOLOGY. 2013;119:703–18
2. Kernohan JW, Woltman HW. Incisura of the crus due to contralateral brain tumour. Arch Neurol Psychiatry. 1929:274–87
3. McKenna C, Fellus J, Barrett AM. False localizing signs in traumatic brain injury. Brain Inj. 2009;23:597–601
4. Derakhshan I. Right sided weakness with right subdural hematoma: Motor deafferentation of left hemisphere resulted in paralysis of the right side. Brain Inj. 2009;23:770–4
5. Derakhshan I, Derakhsan I. Kernohan notch. J Neurosurg. 2004;100:741–2
6. Evans KC, Shea SA, Saykin AJ. Functional MRI localisation of central nervous system regions associated with volitional inspiration in humans. J Physiol. 1999;520(Pt 2):383–92
7. Kiryu S, Loring SH, Mori Y, Rofsky NM, Hatabu H, Takahashi M. Quantitative analysis of the velocity and synchronicity of diaphragmatic motion: Dynamic MRI in different postures. Magn Reson Imaging. 2006;24:1325–32
8. Hiscock M, Kinsbourne M, Green AHammond GE. Is time sharing asymmetry a valid indicator for speech lateralization? Evidence for left handers Cerebral Control of Speech and Limb Movements. 1990 North Holland Elsevier Science Publishers B.V.:pp 611–33 . Edited by
9. Bowers D, Heilman KM, Satz P, Altman A. Simultaneous performance on verbal, nonverbal and motor tasks by right-handed adults. Cortex. 1978;14:540–56
10. Derakhshan I. Laterality of seizure onset and the simple reaction time: Revamping the Poffenberger’s paradigm for seizure surgery. Neurol Res. 2006;28:777–84
11. Derakhshan IArabnis HR, Tran QN. Laterality of motor control or raised intracranial pressure? Physiology not physics aids in understanding the emergence of ipsilateral pyramidal signs in neurosurgery Proceedings of the 2013 International Conference on Bioinformatics and Computational Biology. Athens, Georgia CSREA Press:pp 350–5 Edited by
12. Derakhshan I, Gaillard WD. Atypical language in lesional and nonlesional complex partial epilepsy. Neurology. 2008;70:2266–7
13. Melo TP, de Mendonca A, Crespa M, Carvalho M, Ferro JM. An emegency-room based study of stroke coma. Cerebrovasc Dis. 1992;2:93–101
14. Hamer JF, Lambert WESegalowitz SJ, Gruber FA. Visual fields and cerebral hemisphere preferences in bilinguals Language Development and Neurological Theory. 1977 New York Academic Press:pp 57–62 . Edited by
© 2014 American Society of Anesthesiologists, Inc.