Subclinical Abnormal Gyration Pattern, a Potential Anatomic Marker of Epileptogenic Zone in Patients With Magnetic Resonance Imaging-Negative Frontal Lobe Epilepsy

Service de Neurochirurgie Fonctionnelle et Stéréotaxique, CHU Timone, Assistance Publique des Hôpitaux de Marseille, Marseille, France.
Neurosurgery (Impact Factor: 3.62). 02/2011; 69(1):80-93; discussion 93-4. DOI: 10.1227/NEU.0b013e318212bb1a
Source: PubMed


Epilepsy surgery for magnetic resonance imaging (MRI)-negative patients has a less favorable outcome.
Detection of subclinical abnormal gyration (SAG) patterns and their potential contribution to assessment of the topography of the epileptogenic zone (EZ) is addressed in MRI-negative patients with frontal lobe epilepsy.
Between September 1998 and July 2005, 12 MRI-negative frontal lobe epilepsy patients underwent stereoelectroencephalography with postcorticectomy follow-up of longer than 1 year (average, 3.3 years). Original software (BrainVISA/Anatomist, trained on a database of normal volunteers was used to determine which sulci had morphology out of the normal range (SAG). Topography of the EZ, SAG pattern, corticectomy, postoperative seizure control, and histopathology were analyzed.
At last follow-up, 8 of 12 patients (66.7%) were Engel class I (7 IA and 1 IB), 2 class II, and 2 class IV. Small focal cortical dysplasia was histologically diagnosed in 9 of the 12 patients (75%), including 7 of 8 seizure-free patients (87.5%). A SAG pattern was found to be in the EZ area in 9 patients (75%), in the ipsilateral frontal lobe out of the EZ in 2, and limited to the contralateral hemisphere in 1.
SAG patterns appear to be associated with the topography of the EZ in MRI-negative frontal lobe epilepsy and may have a useful role in preoperative assessment. Small focal cortical dysplasia not detected with MRI is often found on histopathological examination, particularly in the depth of the posterior part of the superior frontal sulcus and intermediate frontal sulcus, suggesting a specific developmental critical zone in these locations.

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    • "Before the implantation of the subdural grid electrodes, volumetric MRI (slice thickness, 2.0 mm; TE, 6.2 milliseconds [ms]; TR, 10.3 ms; flip angle, 8 degrees) was performed on a 3-T Philips ACHIEVA scanner (Philips MRI Equipment, Eindhoven, The Netherlands). Matching of the cortical sulci and gyri was done with Brain VISA software based on T1-weighted MR images.5 6 7 After implantation of the grid, a thin-sliced bone window CT was performed. Both preimplantation MRI and postimplantation CT were incorporated into LGP. "
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    • "Patients with refractory epilepsy due to CD are a challenge for clinicians. There is still a long distance to be covered to achieve complete freedom from seizures (Regis et al., 2011; Chassoux et al., 2012). With the development of neuroimaging technology, the postoperative outcomes convey better results in terms of seizure freedom. "

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    • "FCD II on MRI can be limited to the bottom of a sulcus (Barkovich et al., 1997), with local increased WM signal intensity (Hofman et al., 2011), or form an extensive " transmantle dysplasia " where abnormal signal extends to the margin of the ventricle (Barkovich et al., 1997). Furthermore, in some pathology-proven cases of FCD II, MRI changes are subtle or overlooked (Oster et al., 2012; Regis et al., 2011). These observations suggest that the extent of WM pathology within the spectrum of FCD II lesions is highly variable. "
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