Abstracts

Rationale: Small temporal encephaloceles are a cause of temporal lobe epilepsy easily missed with standard MRI. We report three patients with drug-resistant temporal lobe epilepsy previously considered nonlesional, in whom temporal encephaloceles were confirmed after additional CT or MRI imaging. In a 24 year-old woman undergoing presurgical evaluation, recognition of a small temporal encephalocele on MRI altered subsequent evaluation and surgical treatment. Methods: The index patient had seizures since the age of 20, with an aura of lightheadedness, then loss of hearing in the left ear, and inability to talk, with occasional secondary generalization. She failed trials of phenytoin, valproate, lamotrigine, lacosamide, topiramate, and zonisamide, and had an average of three to four seizures weekly despite adequate oxcarbazepine and levetiracetam doses. Video-EEG in the epilepsy monitoring unit recorded several seizures with lip smacking, left manual automatisms, posturing of the right arm, and post-ictal nose wiping with the left hand, all of which favored a left temporal localization. The EEG ictal onset was left anterior-mid temporal in all the seizures, and the interictal epileptiform activity was also localized to the left temporal region. 3-Tesla brain MRI was interpreted as normal, with no evidence of hippocampal sclerosis. Brain FDG-PET was negative and ictal SPECT did not show clear focal hyperperfusion. Neuropsychological testing was neither localizing nor lateralizing. Bilateral language and memory dominance were found on Wada testing. After re-inspection of the MRI, an encephalocele was suspected in the left inferior-anterior temporal lobe. 7-Tesla MRI confirmed the initial finding and coronal CT of the brain best demonstrated the bone defect at the base of the left anterior middle cranial fossa. The decision was made to proceed with surgical resection with electrocorticography guidance. Results: After surgical exposure of the encephalocele, electrocorticography with grid electrodes covering the left temporal pole and base demonstrated frequent spikes from the medial temporal region proximal to the encephalocele. Following resection of the encephalocele and surrounding brain tissue sparing the hippocampus, electrocorticography did not record any epileptiform discharges. The patient did well postoperatively with no seizures in the past four weeks since surgery. Coronal CT was also crucial to verify small temporal encephaloceles in two other patients now awaiting surgery. Conclusions: Temporal encephaloceles may be an under-recognized cause of drug-resistant temporal lobe epilepsy. They are often discovered incidentally at the time of resection or suspected with careful scrutiny of MRI images. CT coronal sections through the middle cranial fossa will help identify the bone defect associated with encephaloceles. Coronal CT images should be considered in presurgical evaluation of nonlesional temporal lobe epilepsy, in search of small temporal encephaloceles. Discovery of this lesion obviates the need for invasive recordings and allows hippocampal sparing during surgery.