Focal cortical dysplasia type IIb: Completeness of cortical, not subcortical, resection is necessary for seizure freedom

Abstract

SUMMARYPurpose: Focal cortical dysplasia type IIb (FCD IIb) lesions are highly epileptogenic and frequently cause pharmacoresistant epilepsy. Complete surgical resection leads to seizure freedom in most cases. However, the term ''complete'' resection is controversial with regard to the necessity of performing resections of the subcortical zone, which is frequently seen in these lesions on magnetic resonance imaging (MRI). Methods: We retrospectively analyzed 50 epilepsy patients with histologically proven FCD IIb. The extent of surgical resection was determined by SPM5-based coregistration of the preoperative and postoperative MRI scans. Postoperative outcome was analyzed with regard to (1) the completeness of the resection of the cortical abnormality and (2) the completeness of the resection of the subcortical abnormality. Key Findings: Complete resection of the cortical abnormality led to postoperative seizure freedom (Engel class Ia) in 34 of 37 patients (92%), whereas incomplete cortical resection achieved this in only one of 13 patients (8%, p < 0.001). Among the patients with complete cortical resection, 36 had FCDs with a subcortical hyperintensity according to MRI. In this group, complete resection of the subcortical abnormality did not result in a better postoperative outcome than incomplete resection (90% vs. 93% for Engel class Ia, n.s.). Significance: Complete resection of the MRI-documented cortical abnormality in FCD IIb is crucial for a favorable postoperative outcome. However, resection of the subcortical hyperintense zone is not essential for seizure freedom. Therefore, sparing of the subcortical white matter may reduce the surgical risk of encroaching on relevant fiber tracts. In addition, these findings give an interesting insight into the epileptogenic propensity of different parts of these lesions.

The influence of lesion volume, perilesion resection volume, and completeness of resection on seizure outcome after resective epilepsy surgery for cortical dysplasia in children

“…The surgeon, therefore, aims to resect this subcortical lesion, sometimes as deep as the underlying ventricles. Wagner et al, 26 as described above, already found that such subcortical resection does not correlate with improved seizure control.…”

“…Several clinical research groups have studied the impact of different radiological or clinicopathological factors on seizure outcome after extirpative surgery for FCD. [4][5][6][7][8][9][11][12][13][14][15]23,24,26,28,29 Recently, Rowland et al 22 reported on their meta-analysis of predictors of seizure freedom in the surgical management of FCD on the basis of results from 37 selected studies. They noted that complete resection of the anatomical or electrographic abnormality was the most important treatment-related factor predictive of seizure freedom.…”

“…The value of resecting tissue surrounding the identified area of a cortical dysplasia is unclear. Wagner et al 26 noted that in FCD Type 2B, resection of the subcortical radiological abnormality was not necessary for seizure freedom, provided the cortical abnormality had been completely resected. In our study, we noted that when considering only patients with completely resected cortical lesions, seizure control was not significantly associated with increasing perilesional volumes.…”

Magnetic resonance imaging abnormalities in the resection region correlate with histopathological type, gliosis extent, and postoperative outcome in pediatric cortical dysplasia

“…The cause for the increased prevalence in our study is uncertain; however, 3D 1-mm isotropic T2-weighted FLAIR sequences and predominately 3-T images were used and this differs from most prior studies. 6,7,16,22 Interestingly, Wagner et al, 32 in a selected group of 50 predominately adult patients with Type IIb CD (82% lesional), found increased cortical signal in 90% of their patients, 40% of whom underwent 3-T imaging, some with 3D T2-weighted FLAIR sequences. The etiology of this finding is uncertain but may be related to gliosis, cell density, or potentially seizure-related edema.…”

“…A classification of complete resection was given if the entirety of the MRI-documented cortical abnormality was removed. 32 For the purposes of this study, those patients who had functional hemispherotomies and lesional MRI studies with complete resection were considered to have had a complete resection. As this study was not focused on electrophysiology, the relationship of EEG abnormalities and resection was not specifically assessed.…”