Small temporal pole encephalocele: A hidden cause of “normal” MRI temporal lobe epilepsy

Abstract

SUMMARYObjective: Small temporal pole encephalocele (STPE) can be the pathologic substrate of epilepsy in a subgroup of patients with noninformative magnetic resonance imaging (MRI). Herein, we analyzed the clinical, neurophysiologic, and radiologic features of the epilepsy found in 22 patients with STPE, and the frequency of STPE in patients with refractory focal epilepsy (RFE). Methods: We performed an observational study of all patients with STPE identified at our epilepsy unit from January 2007 to December 2014. Cases were detected through a systematic search of our database of RFE patients evaluated for surgery, and a prospective collection of patients identified at the outpatient clinic. The RFE database was also employed to analyze the frequency of STPE among the different clinical subgroups. Results: We identified 22 patients with STPE (11 women), including 12 (4.0%) of 303 patients from the RFE database, and 10 from the outpatient clinic. The median age was 51.5 years (range 29-75) and the median age at seizure onset was 38.5 years (range 15-73). Typically, 12 (80%) of 15 patients with left STPE reported seizures with impairment of language. Among the RFE cases, STPE were found in 9.6% of patients with temporal lobe epilepsy (TLE), and in 0.5% of those with extra-TLE (p = 0.0001). STPEs were more frequent in TLE patients with an initial MRI study reported as normal (23.3%) than in those with MRI-visible lesions (1.4%; p = 0.0002). Stereo-electroencephalography was performed in four patients, confirming the localization of the epileptogenic zone at the temporal pole with late participation of the hippocampus. Long-term seizure control was achieved in four of five operated patients. Significance: STPE can be a hidden cause of TLE in a subgroup of patients with an initial report of "normal" MRI. Early identification of this lesion may help to select patients for presurgical evaluation and tailored resection.

Recommendations for the use of structural magnetic resonance imaging in the care of patients with epilepsy: A consensus report from the International League Against Epilepsy Neuroimaging Task Force

“…Although it is more prevalent in patients than in healthy controls, its relation to epileptogenicity remains unclear. 59 Encephaloceles of the temporal pole [60][61][62] and parahippocampal dysplasia 63 may be underdiagnosed, treatable causes of refractory TLE. Encephaloceles present as a herniation of brain tissue through a defect in the skull base, often the greater wing of the sphenoid bone.…”

MRI‐negative temporal lobe epilepsy—What do we know?

“…Increased use of high magnetic field epilepsy‐protocol 3T(Tesla) MRI scans has pushed many of what used to be considered MRI‐negative TLE cases into the lesion‐positive group, resulting in increased detection of HS, focal cortical dysplasia (FCD), and dysembryoplastic neuroepithelial tumors (DNET) . Small temporal pole encephaloceles are now recognized for being a hidden cause of “MRI‐negative” TLE . Furthermore, cases of TLE with ipsilateral amygdala enlargement have recently gained recognition for being a possible subtype of MRI‐negative TLE.…”

Morphometric correlates of anomia in patients with small left temporopolar lesions

“…It might be possible that both aspects are interacting, since focal cortical dysplasias in epilepsy population have been associated with abnormalities in cortical gyrification (Adler et al ., ). Although there is less evidence in cases of encephaloceles, a possible association between encephaloceles and an alteration of normal cortical lamination has been described (Giulioni et al ., ; Toledano et al ., ), which could then account for the reduced gyrification.…”

“…The scanning protocol included three magnetic resonance imaging (MRI) modalities, but only the T1‐weighted 3D MPRAGE was selected for all the participants, echo time (TE) = 4.44 ms; repetition time (TR) = 2,400 ms; field of view (FOV) = 240 × 240 × 160 mm 3 ; and voxel size, 0.9375 × 0.9375 × 1 mm 3 . The T2‐weighted as well as FLAIR acquisitions were evaluated by two experienced neurologists for the clinical assessment (Toledano et al ., ). Structural MRI showed discrete lesions (five encephaloceles and seven focal cortical dysplasias) that were well circumscribed and involved the temporopolar cortex in all the patients.…”

“…The current study aimed to characterize the neuroanatomical correlates of omission errors during object naming. With this goal, we availed of a group of patients with epilepsy associated with a small epileptogenic lesion (i.e., encephalocele and cortical dysplasia) centred at the tip of the left temporal pole (Toledano et al ., ; Toledano et al ., ). These lesions are by far more restricted than those reported in earlier studies, allowing us to avoid the confounds inherent to extensive lesions (Mah, Husain, Rees, & Nachev, ; Mesulam et al ., ; Xu, Jha, & Nachev, ).…”