Breach Rhythm Beyond Skull Defects: Clinical and Functional Insights from a Bilateral Lesion Case

Breach rhythm (BR) is a well-recognized EEG pattern characterized by high-amplitude, sharply contoured fast activity over areas of skull defect, most often following craniotomy or trauma. Although considered physiological, BR may closely mimic epileptiform discharges, leading to diagnostic uncertainty. We report a 33-year-old man with bilateral skull defects secondary to traumatic brain injury who presented with recurrent generalized tonic-clonic seizures. EEG showed continuous fast and sharp activity over the right F4-C4 region, consistent with BR, and diffuse slow waves over the left hemisphere. During two focal seizures, ictal discharges originating from the right F8 electrode transiently modified the morphology and rhythmicity of the ongoing BR before spreading bilaterally. Interestingly, no BR was observed over the left hemisphere despite a large skull defect, likely reflecting severe cortical injury. Following treatment with levetiracetam and phenytoin, seizures resolved, while the right-sided BR persisted unchanged. This case highlights that BR is not merely a passive artifact of altered conductivity but a dynamic indicator of cortical function. Its modulation during seizures and absence over structurally damaged cortex support the concept that BR may serve as a potential marker of cortical viability. Recognizing these patterns may prevent misinterpretation of physiological BR as epileptiform activity and enhance EEG evaluation in patients with structural brain lesions.