How is symmetry identified in the visual analysis of neonatal electroencephalogram (EEG)?

Updated: Nov 08, 2018
  • Author: Samuel Koszer, MD; Chief Editor: Selim R Benbadis, MD  more...
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Answer

Answer

Symmetry: Neonatal records with voltage asymmetries of 25% or more are abnormal. Noncerebral hemisphere abnormalities should be excluded when evaluating records for amplitude abnormalities. These noncerebral hemisphere abnormalities include unilateral cephalhematomas, subgaleal or scalp edema, and technical faults (eg, asymmetric placement of electrodes, sweating, smearing of electrode paste). Because of the nature of their lesions, neonates exhibiting this pattern often develop seizures. Ictal EEG discharges can be seen over the depressed side, and sustained focal discharges superimposed on this abnormal background represent the rare occurrence of focal ictal events in direct proximity with underlying anatomical lesions.

  • Transient interhemispheric asymmetry is likely a normal variant. A sudden, markedly exaggerated TA pattern approaching a BS pattern involving only one hemisphere while the other hemisphere maintains normal features is seen occasionally. This finding may be indicative of a focal lesion.

  • Persistent attenuation of voltage involving only one scalp region can be associated with focal or lateralized neuropathological lesions. The technician must be aware that improper placement of electrodes or localized scalp edema can result in an EEG pattern that resembles focal attenuation. See the image below.

    Voltage attenuation, focal. An infant of 40 weeks' Voltage attenuation, focal. An infant of 40 weeks' postconceptional age with a left middle cerebral artery infarction and intermittent posturing and hyperextension of the neck. Background activity demonstrates attenuation of delta and fast activity on the left indicative of a structural lesion on the left.

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