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Stereotactic EEG, intraoperative electrocorticography and brief potentially ictal rhythmic discharges (BIRDs)

We highlight recent reviews concerning stereotactic EEG, intraoperative electrocorticography and brief potentially ictal rhythmic discharges (BIRDs).

When considering resective surgery for focal drug-resistant epilepsy, intracranial electroencephalogram (EEG)  can help to localise the epileptogenic zone (EZ) when non-invasive investigations, including scalp EEG, yield results of insufficient certainty.  Dasgupta and colleagues (1) explored stereotactic EEG (SEEG) with implanted depth electrodes and how this approach has largely replaced intracranial EEG with subdural grids and strip electrodes.  They discuss advances in SEEG in epilepsy surgery planning, including augmented reality, robotic-assisted surgical techniques and artificial intelligence.  In some cases, additional confirmatory data is sought for EZ delineation with intraoperative electrocorticography (iECoG), although this approach is not without controversy. Goel et al. (2) performed a meta-analysis to evaluate the clinical usefulness of iECoG in resective epilepsy surgery.  An individual-patient level data analysis showed an association between iECoG and favourable post-operative seizure outcomes in focal cortical dysplasia (number needed to treat (NNT) was 4.7) compared to all epilepsy aetiologies (NNT 8.8).  The authors therefore postulated that the utility of iECoG may vary by pathology. 

Yoo (3) examined the ill-defined scalp EEG pattern termed brief potentially ictal rhythmic discharges (BIRDs) which has been observed in neonates, critically ill adults and adults with epilepsy. Consensus on the definition and clinical significance is evolving, but the presence of BIRDs carries an increased risk of seizures and may help to predict the seizure-onset zone. In critically ill patients, there is an association with BIRDs and acute brain injury and extended EEG monitoring may be required to guide management.  In non-critically ill adults, BIRDs may reflect a greater risk of drug-resistant epilepsy.

Key Points:

  • Stereotactic EEG with implanted depth electrodes has largely replaced intracranial EEG with subdural grids and strip electrodes in planning resective surgery for epilepsy.
  • The clinical utility of stereotactic EEG in preoperative evaluations may vary by pathology but is especially high for cortical dysplasia.
  • Consensus is evolving surrounding the technical definition and clinical significance of brief potentially ictal rhythmic discharges.


  1. Previous, current, and future stereotactic EEG techniques for localising epileptic foci. Dasgupta D, Miserocchi A, McEvoy AW, Duncan JS. Expert Rev Med Devices. 2022 Jul;19(7):571-580. doi: 10.1080/17434440.2022.2114830. Epub 2022 Aug 24. PMID: 36003028; PMCID: PMC9612928. pubmed.ncbi.nlm.nih.gov/36003028/
  2. Clinical utility of intraoperative electrocorticography for epilepsy surgery: A systematic review and meta-analysis. Goel K, Pek V, Shlobin NA, Chen JS, Wang A, Ibrahim GM, Hadjinicolaou A, Roessler K, Dudley RW, Nguyen DK, El-Tahry R, Fallah A, Weil AG. Epilepsia. 2023 Feb;64(2):253-265. doi: 10.1111/epi.17472. Epub 2022 Dec 12. PMID: 36404579. pubmed.ncbi.nlm.nih.gov/36404579/
  3. BIRDs (Brief Potentially Ictal Rhythmic Discharges) watching during EEG monitoring. Yoo JY.  Front Neurol. 2022 Aug 23;13:966480. doi: 10.3389/fneur.2022.966480. PMID: 36081872; PMCID: PMC9445572. www.ncbi.nlm.nih.gov/pmc/articles/PMC9445572/"

Alexandra Balatskaya, Epilepsy Center, Hamburg

Publish on behalf of the Scientific Panel on Epilepsy