Rationale: Temporal lobe encephaloceles are increasingly identified as a source of medically refractory epilepsy. Improvements in high resolution imaging and increased clinical suspicion may aid in early detection of these lesions and allow tailored surgical resections that may render these patients seizure free. However, when electroclinical, imaging and semiological data are discordant, the suspicion for dual pathology should be raised. Dual pathology may exist in up to 15% of patients with encephaloceles. Invasive studies are often prudent to differentiate this dual pathology from epileptogenesis arising solely from encephalocele and in delineating involvement of the mesial temporal structures. We present a series of patients that underwent invasive evaluation at our institution in the workup of encephaloceles due to discordant pre-surgical workup. Methods: This retrospective descriptive study reviewed six patients with epilepsy and encephaloceles at the Cleveland Clinic between January 2000 and May 2020 who underwent invasive evaluation with stereotactic EEG. Data collection included encephalocele characteristics, ancillary testing in the pre-surgical evaluation (EEG, MRI, PET, SPECT), invasive findings, pathological findings, surgical management, post-surgical seizure outcomes (see Table 1). Results: Six patients with intractable epilepsy and left temporal lobe encephaloceles underwent invasive evaluation with SEEG to elucidate the epileptogenic zone. The average age was 31 years old (27-42) and 50% were females. Scalp EEG evaluation revealed regional temporal ictal patterns in four patients (two extratemporal). MRI revealed encephaloceles in four patients, bilateral in one patient. Two patients with MRI “negative lesions” were found to have encephaloceles intraoperatively. PET scan was concordant with regional hypometabolism in all six patients and ictal SPECT was concordant in 4/5 patients (80%). Invasive evaluation revealed seizures arising from the temporopolar region without involvement (or late) of the hippocampus in 5/6 patients. A tailored resection sparing the hippocampus was performed in all patients (6/6) with favorable outcomes (Engel I) in 83% (5/6) with a follow-up of at least nine months (9-45 months) seizure freedom. Dual pathology was found in one patient with seizures arising from the left frontal and temporal region. Pathology showed gliosis in all patients with coexistent focal cortical dysplasia type I in 3/6 (50%). Patient #6 continues to have seizures with unchanged frequency now managed with neuroresponsive stimulation.Figure 1 illustrates a case of dual pathology associated with encephalocele in a 28-year-old right-handed man. EEG showed left frontal seizures. He underwent a lesionectomy and left frontal / orbitofrontal resection with 45-months seizure freedom. Conclusions: Anatomo-electroclinical correlations remain paramount when evaluating encephaloceles as substrates for intractable epilepsy. Our cases illustrate the importance of invasive evaluation when dual pathology is present and in determining the extent of resection. In our cases PET and SPECT provided good concordance in the pre-surgical workup. However, when discordance is present invasive evaluations may prove prudent in delineating the epileptogenic zone. Good surgical outcomes (Engel I) are possible with a limited tailored resection of the temporal lobe sparing the hippocampus. This study expands on the importance of invasive evaluation during workup of dominant temporal lobe encephaloceles when the following scenarios arise in clinical practice: 1) pre-surgical ancillary testing is discordant 2) dual-pathology is present 3) involvement of hippocampal structures in the epileptogenesis is not well determined. Funding: Please list any funding that was received in support of this abstract.: None
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