Vasogenic oedema during stereoelectroencephalography: intracranial pattern and late-onset clinical repercussion.

In patients suffering from focal drug-resistant epilepsy, intracranial explorations are the gold standard for identifying the epileptogenic zone and evaluating the possibility of a surgical resection. Amongst them, stereoelectroencephalography (SEEG), using depth electrodes, is a safe procedure. However, complications occur on average in 2% of cases, notably haemorrhages or infections. Vasogenic cerebral oedema constitutes a rarely reported complication. Amongst the 85 patients explored with SEEG between January 2017 and September 2023, three had a clinically and electrophysiologically relevant vasogenic cerebral oedema. In these three patients, the surgical procedure was uneventful. In all three as well, electrodes exploring areas away from the epileptogenic zone recorded some unexpected focal delta slowing with clinically asymptomatic superimposed discharges, a pattern so far only reported in cases of bleeding. Moreover, one patient experienced confusion 10 days after explantation. Post-explantation magnetic resonance imaging showed, in all three patients, a vasogenic oedema that fully resolved a few months later. We did not identify any contributing factors, and there were no particularities concerning the number of electrodes, their implantation site or the recording duration. Focal delta slowing and rhythmic discharges during SEEG can indicate a vasogenic oedema. Clinical consequences can occur after explantation. Evolution is favourable but this misleading pattern must be identified.