Abstracts

Rationale: Encephaloceles are protrusions of brain parenchyma through a structural defect in the skull base.While encephaloceles can occur in any region of the skull, recent studies have begun to evaluate the association between temporal or middle cranial fossa encephaloceles (MCFE) and epilepsy, as these may be a curable cause of seizures.[i],[iii] These lesions are often occult and can be missed with standard imaging modalities, likely resulting in under-diagnosis[ii]. In the majority of studies of encephaloceles and epilepsy, epilepsy patients are first identified, then evaluated for encephaloceles. However, encephaloceles can be findings incidentally detected on imaging performed for other reasons. Our study describes the clinical characteristics of patients with MCFE identified on intracranial imaging obtained for any reason at a tertiary care center, and to evaluate the potential association between MCFE and epilepsy. [i]Gasparini S, et al.; Neurology, 2018;90:e1200-e1203. [ii]Abou-Hamden A, et al., Epilepsia. 2010 Oct;51(10):2199-202. [iii]Van Gompel J, Miller, J, Neurology, 2015;85:1440-1441 Methods: This study was a retrospective chart review performed at OHSU. Subjects with MCFEs were identified by a Neuroradiologist during routine evaluation of brain CT and MRI images from 1/2000 to 4/2019. The medical records of included subjects were reviewed for neurological diagnoses, epilepsy data and brain pathology reports. Risk factors for seizure and epilepsy (not including MCFE) were obtained, which included genetic, structural, autoimmune, and metabolic abnormalities in addition to family history of epilepsy, history of febrile seizure, prior CNS infection, and possible head trauma and traumatic brain injury (TBI). The MRI and CT images of the included subjects were reviewed by an independent Neuroradiologist to confirm the presence of MCFE.  Results: Ninety-three patients with MCFE were identified. 37.6% (35) had a history of at least 1 seizure, and 34.4% (32) met ILAE criteria for the diagnosis of epilepsy.[i]  Of the 32 epilepsy patients, 50% (16) had no known risk factors for epilepsy (see table for further details). Of the 32 epilepsy patients, 53.1% (17) had temporal lobe epilepsy (TLE).  6.25% (2) had generalized epilepsy, 25% (8) had non-TLE, and 15.6% (5) had poorly localizing or unknown localization of their epilepsy. Of the patients with TLE, 76.5% (13/17) had no clear risk factors for epilepsy. [i]Fisher RS et al. Epilepsia 2014; 55:475-482. Conclusions: Our cohort represents one of the largest groups of middle cranial fossa encephalocele patients characterized to date. Of those epilepsy patients with MCFE, 50% had no clear risk factors for epilepsy other than encephalocele, including a majority of patients with TLE (76.5%).Though we focused on MCFE, which has been associated with TLE, 46.9% of epilepsy patients in this study did not have TLE. This finding may inform future studies evaluating the epileptogenic potential of encephaloceles, as previous studies have frequently focused solely on patients with TLE or who are candidates for temporal resections. The majority of epilepsy patients in this study were without known epilepsy risk factors (68.8%). This suggests that MCFE should considered in patients with epilepsy of unknown etiology. The majority of patients with encephalocele in the study were women, and were more likely to have no known risk factors for epilepsy and have TLE. This may suggest that MCFE may be an important consideration as a potential etiology in female epilepsy patients with TLE of unknown etiology.  Funding: No funding