Abstracts

Rationale: This case report depicts the electroclinical features of seizure spread between the epileptogenic zone and primary visual cortex in a patient with photo-convulsive response on stereotactic EEG (sEEG). Prior studies have described elementary visual phenomena arising from the occipital cortex. However, propagation from the basal temporal lobe to the primary occipital cortex may trigger similar phenomenon. This may be explained by the inferior longitudinal fasciculus (ILF) that connects the occipital cortex and the temporal lobe. In this report, we present the case of a 19-year-old woman with medically refractory focal epilepsy in which the photic-induced epileptic network originated within the posterior collateral sulcus with spread to the primary visual cortex proven by sEEG.

Methods: As part of the pre-surgical evaluation, the patient underwent sEEG monitoring to further elucidate the epileptogenic zone and spread of seizures. Additionally, responses to photic stimulation and repetitive blinking were assessed.

Results: A 19-year-old woman presented with seizures described as right hemivisual field distortion with “black crescent shape” and colored flashing lights that progressed to formed images, words, and shapes. Additionally, her hearing would become “muffled” with rare secondary generalization. Post-ictal state consisted of tiredness and headaches. Scalp EEG monitoring showed interictal activity with spikes in the left occipital and parieto-occipital regions. MRI of the brain revealed left choroidal fissure cyst with mass effect on the left hippocampus as well as left a possible posterior para hippocampal cortical dysplasia. Ancillary testing (fMRI, MEG, VBM, and PET) suggested the epileptogenic zone was localized to the left calcarine, left basal temporal or left basal temporo-occipital junction.

The patient subsequently underwent sEEG evaluation that revealed interictal activity localized to the posterior collateral sulcus that spread to the lateral occipital sulcus. There was increased interictal activity associated with repetitive blinking that was time locked. The activity was present in the collateral sulcus posteriorly, lateral occipital region and supra and infra calcarine regions. (Figure 1) Spontaneous seizures had a clear onset in the posterior collateral sulcus that spread to the lateral occipital sulcus followed by spread to both infra- and supra-calcarine electrodes causing her typical semiology. One seizure was triggered after photic stimulation (15Hz) with the same electroclinical correlation. Based on above findings, she underwent successful resection and laser ablation.

Conclusions: Our case highlights the importance of the exploration of the basal temporal region as a possible area that may present with visual phenomenon. This may be explained by spread to the primary visual region through the inferior longitudinal fasciculus. Double directionality of ILF seems to be the explanation for the temporal to occipital connectivity seen in the present case. Finally, occipital phenomenon with photoparoxysmal response can be present as the first manifestation in basal temporal lobe epilepsy.

Funding: Please list any funding that was received in support of this abstract.: None.