Breach rhythm: the EEG related to skull defects

Area of Science:

• Neurophysiology
• Clinical Electrophysiology
• Neurosurgery

Background:

• Skull defects can alter electroencephalography (EEG) patterns.
• Previous studies suggest potential changes in brain rhythms over cranial defects.
• The nature and significance of these EEG alterations require further investigation.

Purpose of the Study:

• To investigate EEG changes in patients with skull defects.
• To characterize focal rhythms observed over cranial defects, termed 'breach rhythms'.
• To explore the relationship between breach rhythms, bone replacement, and clinical conditions like epilepsy and tumor recurrence.

Main Methods:

• Recorded 89 EEGs from 33 patients with skull defects, with X-ray confirmation of electrode placement.
• Performed serial EEGs in some patients before and after bone (or acrylic) replacement.
• Analyzed focal rhythms, their characteristics, responsiveness to stimuli, and effect of surgical intervention.

Main Results:

• Observed potential increases in alpha and frontal fast rhythm amplitudes over defects.
• Identified sharply focal, mu-like rhythms (6-11 c/sec) in 21 cases near electrodes C3 and T3, termed 'breach rhythms'.
• Breach rhythms showed varied responsiveness to stimuli and were not consistently abolished by bone replacement.
• Breach rhythms, even spike-like, showed little correlation with epilepsy or tumor recurrence.

Conclusions:

• The focal rhythms observed over skull defects ('breach rhythms') are distinct from enhanced normal mu rhythm.
• Breach rhythms are not reliable indicators of epilepsy or tumor recurrence.
• Bone replacement has a variable effect on breach rhythms.