Focal cortical dysplasias: MR imaging, histopathologic, and clinical correlations in surgically treated patients with epilepsy

Abstract

Background and purpose: Focal cortical dysplasia (FCD) covers a spectrum of conditions in which the neuropathologic and electroclinic presentations and the surgical outcomes vary. The aim of this study was to identify the MR features of histologic subtypes of FCD that would be useful for differential diagnosis.

Methods: We reviewed the MR data of 49 patients treated surgically for intractable partial epilepsy, who received a histologic diagnosis of FCD not associated with other brain abnormalities except hippocampal sclerosis and who were classified by histologic criteria as having architectural dysplasia (28 patients), cytoarchitectural dysplasia (six patients), or Taylor's FCD (15 patients).

Results: From the MR features, it was generally possible to distinguish Taylor's FCD from architectural or cytoarchitectural dysplasias (non-Taylor's FCD). Findings suggesting Taylor's FCD were focal cortical thickening, blurring of the gray-white matter junction, and hyperintensity (on T2-weighted images) of subcortical white matter often tapering toward the ventricle. Focal brain hypoplasia with shrinkage and moderate signal intensity alterations in the white matter core were present in most patients with architectural dysplasia. The lesion was generally extratemporal in Taylor's FCD and temporal in architectural dysplasia. Ipsilateral hippocampal sclerosis was often present in architectural dysplasia (dual abnormality).

Conclusions: In patients with FCD, Taylor's FCD and non-Taylor's FCD can usually be distinguished with MR imaging, although some overlap exists. A provisional MR diagnosis is important for presurgical investigations and surgical planning and may have prognostic implications.

Fig 1.

Photomicrographs show the histologic characteristics of the FCD subtypes. A, Architectural dysplasia characterized by moderate derangement of cortical lamination, with neurons of the same shape and size scattered throughout the cortex (Kluver-Barrera stain; original magnification, ×250). B, Cytoarchitectural dysplasia. Note the cluster of cytomegalic neurons with satellitosis (arrows) (Kluver-Barrera stain; original magnification, ×250). C, Taylor’s FCD with balloon cells. Note large balloon cell characterized by homogeneous eosinophilic cytoplasm and peripheral nucleus with prominent nucleolus (arrow) (hematoxylin-eosin stain; original magnification, ×250). D, Taylor’s FCD with balloon cells. Note large dysmorphic neurons containing abundant cytoplasmic neurofilaments (arrows) (Bielchowsky stain; original magnification, ×250).

Fig 2.

MR images of Taylor’s FCD with balloon cells. A, Coronal turbo SE IR T1-weighted image (3000/20/400/2) demonstrates thickening of the right frontal cortex with loss of demarcation between gray and white matter and decreased white matter signal intensity (arrow) tapering toward the ventricle. B, Coronal turbo SE T2-weighted image (2300/100/4) and C, coronal turbo SE FLAIR T2-weighted image (6000/100/2000/3), obtained at the same level as A, show increased signal intensity (arrow) of the subcortical white matter extending to the ventricle as a radial band. No mass effect is present.

Fig 3.

MR images of Taylor’s FCD without balloon cells. A, Transverse SE T2-weighted image (2300/90/1) shows extensive hyperintense lesion in the left temporo-occipitobasal region, with no mass effect on adjacent structures. B, Coronal turbo SE IR T1-weighted image (3000/20/400/2) better demonstrates thickening of the cortex (arrows) with blurring of the gray-white matter junction and subcortical white matter hypointensity. C, Coronal turbo SE FLAIR T2-weighted image (6000/100/2000/3) reveals that the hyperintensity of the lesion mainly involves the subcortical white matter (arrows). The ventricular trigone is enlarged on the left.

Fig 4.

MR images of cytoarchitectural dysplasia. A, Coronal turbo SE IR T1-weighted image (3000/20/400/2), B, coronal turbo SE T2-weighted image (2300/100/4), and C, sagittal turbo SE T2-weighted image of a 3D volume acquisition (2100/130/1). Note reduced demarcation of the gray-white matter boundary in the right temporal lobe, with marked signal intensity alterations of subcortical white matter, which is hypointense on the T1-weighted image in A and hyperintense on the T2-weighted images in B and C. These alterations induced us to diagnose Taylor’s FCD. Note, however, that the thickening of the cortex (arrows in A and B), is only mild. This is a case of histologic cytoarchitectural dysplasia resembling Taylor’s FCD.

Fig 5.

MR images of architectural dysplasia and ipsilateral hippocampal sclerosis (dual abnormality). A, Coronal turbo SE T2-weighted image (2300/100/4) reveals hypoplasia of right temporal pole with white matter hyperintensity. B, Transverse SE T2-weighted image (2300/90/1) confirms reduced volume of right temporal pole compared with the contralateral side, with enlargement of the overlying subarachnoid space. C, Coronal turbo SE T2-weighted image (2300/100/4) shows right hippocampal head (arrow), characterized by atrophy and signal hyperintensity, suggesting hippocampal sclerosis.