Focal Cortical Dysplasias in Eloquent Cortex: Functional Characteristics and Correlation with MRI and Histopathologic Changes

Abstract

Summary:Purpose: Focal cortical dysplasia (CD) is increasingly recognized as a common pathologic substrate of medically intractable epilepsy. As these lesions are often localized in the frontal lobe (therefore in potentially eloquent cortex), an understanding of the functional status of the involved region(s) and of its anatomic and pathologic correlates is of prime importance. The purpose of this study is to assess the function of focal CD in relation to magnetic resonance imaging (MRI) and histopathologic features.Methods: Eight patients operated on for medically intractable epilepsy with histologically proven focal CD involving putative eloquent cortex in the frontal lobe (perirolandic and Broca's areas) were included in the study. Functional regions (motor and language) and epileptogenic areas were assessed by extraoperative electrocorticographic recording and electrical cortical mapping. Cortical functions were correlated with the extent of epileptogenicity on electrocorticographic recordings, MRI features, and histologic characteristics.Results: Language or motor areas were colocalized with epileptogenic regions (n ‫ס‬ 6 of 8, 75%), but were not mapped in regions of increased signal on fluid-attenuated inversion recovery (FLAIR) MRI (when they were identified) on preoperative MRI (n ‫ס‬ 5 of 5, 100%). Histologically, balloon cells were almost exclusively found in nonfunctional regions with FLAIR MRI abnormalities. When resected, regions of motor cortex were characterized by cortical dyslamination, columnar disorganization, and dysmorphic neurons, but were devoid of balloon cells. Conclusions:We found an absence of language or motor functions in perirolandic and Broca's areas that showed decreased epileptogenicity, histopathological evidence of CD with balloon cells and FLAIR MRI signal increase. Language and motor functions were present in epileptogenic and dysplastic areas with no balloon cells and no FLAIR signal abnormalities. These findings have implications on options for epilepsy surgery in patients with CD.

Discrepancies between Preoperative Stereoencephalography Language Stimulation Mapping and Intraoperative Awake Mapping during Resection of Focal Cortical Dysplasia in Eloquent Areas

“…These results are in agreement with the ones reported by Chassoux et al [8] where an FCD identified by MRI corresponded to EZ in 3 out of 6 patients. Moreover, Marusic et al [13] found that ictal onset electrodes were those adjacent to FLAIR abnormalities, and even distant in 2 cases out 8, but not within the FCD.…”

“…Even though classically the surgical outcome in FCD has been shown to be worse when compared to temporal lobe epilepsy [4], the introduction of high-resolution MRI techniques [5][6][7] and the extensive use of electrophysiological recordings with stereoencephalography (SEEG) [8][9][10][11] or electrocorticography [12][13][14][15][16] has improved surgical prognosis and long-term outcome [10,[17][18][19][20]. Furthermore, electrophysiology allows both, tracking of epileptogenic activity and functional mapping before surgery when the dysplasia is located in eloquent cortex [21,22] .…”

“…One of the most significant discussions concerns whether or not the function is present within dysplasic tissue. Some authors have reported a lack of function if balloon cell types were present in the dysplasia [13]. For others, the dysgenic cortex may retain essential motor and language functions [23,24] .…”

The surgically remediable syndrome of epilepsy associated with bottom-of-sulcus dysplasia

“…14,[18][19][20][21][22] They seemingly contain no normal function, as suggested by their PET hypometabolism, perilesional fMRI activation, displaced motor functions on cortical stimulation, and absence of deficits following resection. 13,[23][24][25][26] In addition, seizure-free rates after surgery are as high as 90% if completely resected. 9,13,[27][28][29][30][31][32][33][34] Thus, patients with refractory epilepsy and BOSD are ideal candidates for epilepsy surgery.…”

Speech arrest with stimulation may not reliably predict language deficit after epilepsy surgery

“…A recent study found evidence that cortical lesions with balloon cells are less likely to harbor physiologic activity as compared with dysplastic lesions without balloon cells. 6 Transfer of language to the right hemisphere has been found after early injuries in young children, i.e., before age 5 to 9 years, although dysplasia is not necessarily associated with language relocation. [7][8][9] Because some aggravation was noted after the second operation, the resected region participated to a certain degree in languagerelated tasks; however, its resection did not lead to major speech or comprehension alterations.…”