Abstract
Breach rhythm, the hallmark of skull defect, is a familiar finding in the electroencephalogram (EEG). A hole in the skull can also give rise to unfamiliar EEG findings. We present 3 patients with a skull defect whose scalp EEG showed focal epileptiform discharges that resembled F4 electrode artifacts—a 23-year-old man with a right-sided craniectomy for traumatic brain injury, a 63-year-old woman with a history of bifrontal craniectomy and meningioma resection, and a 77-year-old woman who had a right hemicraniectomy for a life-threatening subdural hematoma. In all 3 patients, the F4 electrode was directly above or near a skull defect, and scalp EEG showed phase-reversing waves in FP2-F4 and F4-C4 with no clear-cut “physiological field” (even when the EEG was displayed at a higher sensitivity). In the first 2 patients, the technologist tried to eliminate the “electrode artifacts” by cleaning the scalp thoroughly, replacing the F4 electrode, and maintaining electrode impedance between 2 and 5 kΩ. These measures failed to eliminate the “electrode artifacts” so the EEG was recorded from four 10-10 electrode sites around F4. Extending the montage made it clear that what appeared as F4 electrode artifacts were actually focal epileptiform discharges. Correlation with other electroclinical and neuroimaging data was enough to resolve this issue in the third patient, obviating the need to extend the montage. When recording and interpreting the EEG of patients with a craniotomy or craniectomy, EEG professionals should be aware that focal epileptiform discharges can masquerade as electrode artifacts.
Highlights
The enhanced or high-amplitude rhythmic activity seen in the electroencephalogram (EEG) of individuals with a skull defect is known as breach rhythm.[1,2]
In all 3 patients, in whom the F4 electrode was directly above or near a skull defect, the scalp EEG showed phase-reversing waves in FP2-F4 and F4-C4 with no clear-cut “physiological field”
When the EEG was recorded from four 10-10 electrode sites around F4, it became clear that the F4 phase reversals were focal epileptiform discharges, not electrode artifacts
Summary
The enhanced or high-amplitude rhythmic activity seen in the electroencephalogram (EEG) of individuals with a skull defect is known as breach rhythm.[1,2] A hole in the skull can modify the appearance of EEG waves by altering the propagation of EEG signals from the cortex to the scalp.[3]. The following 3 cases will illustrate that a skull defect may modify the scalp EEG appearance of cortically generated epileptic discharges to the extent that focal epileptiform discharges no longer exhibit a physiological field and can be mistaken for electrode artifacts on a standard bipolar montage. EEG monitoring showed high-amplitude waves with phase reversals in FP2-F4 and F4-C4 F4 Because these waves did not show a clear-cut “physiological field”—even when display sensitivity was increased from 7 to 3 μV/mm— they were thought to be F4 electrode artifacts (Figure 1: EEG1). An extended montage was constructed (Figure 1: EEG2) This simple maneuver proved that what appeared as F4 electrode artifacts were focal epileptiform discharges with an exceptionally “compact” electric field, that is, voltage drop was rapid at short distances from the peak. The same issue was virtually resolved in patient 3, not by adding electrodes and extending the montage, but through hindsight (our experience with the first 2 patients) and by taking other findings into consideration (focal periodic epileptiform discharges and focal seizures in F4 and T4)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Journal of investigative medicine high impact case reports
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
