Focal cortical dysplasia - review

Abstract

Focal cortical dysplasia is a malformation of cortical development, which is the most common cause of medically refractory epilepsy in the pediatric population and the second/third most common etiology of medically intractable seizures in adults.Both genetic and acquired factors are involved in the pathogenesis of cortical dysplasia. Numerous classifications of the complex structural abnormalities of focal cortical dysplasia have been proposed - from Taylor et al. in 1971 to the last modification of Palmini classification made by Blumcke in 2011. In general, three types of cortical dysplasia are recognized.Type I focal cortical dysplasia with mild symptomatic expression and late onset, is more often seen in adults, with changes present in the temporal lobe.Clinical symptoms are more severe in type II of cortical dysplasia usually seen in children. In this type, more extensive changes occur outside the temporal lobe with predilection for the frontal lobes.New type III is one of the above dysplasias with associated another principal lesion as hippocampal sclerosis, tumor, vascular malformation or acquired pathology during early life.Brain MRI imaging shows abnormalities in the majority of type II dysplasias and in only some of type I cortical dysplasias.THE MOST COMMON FINDINGS ON MRI IMAGING INCLUDE: focal cortical thickening or thinning, areas of focal brain atrophy, blurring of the gray-white junction, increased signal on T2- and FLAIR-weighted images in the gray and subcortical white matter often tapering toward the ventricle. On the basis of the MRI findings, it is possible to differentiate between type I and type II cortical dysplasia. A complete resection of the epileptogenic zone is required for seizure-free life. MRI imaging is very helpful to identify those patients who are likely to benefit from surgical treatment in a group of patients with drug-resistant epilepsy.However, in type I cortical dysplasia, MR imaging is often normal, and also in both types the lesion seen on MRI may be smaller than the seizure-generating region seen in the EEG. The abnormalities may also involve vital for life brain parts, where curative surgery will not be an option. Therefore, other diagnostic imaging techniques such as FDG PET, MEG, DTI and intra-cranial EEG are widely used to establish the diagnosis and to decide on management.With advances in both genetics and neuroimaging, we may develop a better understanding of patients with drug-resistant epilepsy, which will help us to provide more successful pharmacological and/or surgical treatment in the future.

Keywords: FCD; epilepsy; focal cortical dysplasia.

Figure 1.

Focal cortical dysplasia type Ia with ipsilateral hippocampal sclerosis (“dual pathology”) in a 31-year-old female by Blumcke IIIa. Coronal MR images: turbo spin-echo inversion-recovery T1-weighted (A,D), turbo spin-echo T2-weighted (B,E), turbo spin-echo FLAIR T2-weighted (C,F) obtained respectively at the level of the temporal pole and the head of the hippocampus. Hypoplasia of the right temporal pole is recognizable, with volume loss of the white matter which leads to mild hyperintensity on T2-weighted images. Mild blurring of the cortical-white matter junction is visible on both T1- and T2-weighted images (A–C). The right hippocampus is atrophic, with decreased signal on IR-T1W images and increased signal on T2W images, consistent with hippocampal sclerosis. Courtesy of dr Norico Salamon. Epileptic Disorders, 2009; 11, 194–205.

Figure 2.

Focal cortical dysplasia type Ia of the right frontal cortex in a 9-year-old boy TSE IR T1WI (A) and TSE T2WI (D). Coronal TSE IR T1WI (B,C) and coronal TSE FLAIR T2WI (E,F). Abnormal gyration along the right frontal convexity (arrows) with mild blurring of the GM/WM junction and mild hypoplasia of the anterior frontal lobe. No signal alterations of the subcortical WM are seen. Courtesy of dr Norico Salamon. Epileptic Disorders, 2009; 11, 194–205.

Figure 3.

Focal cortical dysplasia type IIb of the left frontal cortex in a 9-year-old female. Transverse TSE T2WI (A) and transverse TSE IR T1WI (B). Sagittal TSE FLAIR T2WI (C). Coronal TSE IR T1WI (D), coronal TSE T2-WI (E) and coronal TSE FLAIR T2WI (F). Thickening of the left paramedian frontal cortex which shows a blurred demarcation with the white matter both on T1W and T2W either transverse and coronal images (white arrows, A,B,D,E). On FLAIR coronal sequence (F) the junction between GM/WM seems to be more defined (black arrow), contrary to what is observed most frequently. The hyperintensity of the WM, extending toward the ventricle (transmantle sign) is better appreciated on FLAIR sequences (white arrows, C,F). Courtesy of dr Norico Salamon. Epileptic Disorders, 2009; 11, 194–205.

Figure 4

Focal cortical dysplasia type IIb of the right frontal cortex in a 41-year-old female. Transverse TSE T2WI (magnification) (A); coronal TSE IR T1WI (B) and coronal TSE FLAIR T2WI (C). Sagittal TSE IR T1WI (D) and sagittal TSE FLAIR T2WI (E). Abnormal gyration of the left frontal cortex which presents very sharp demarcation with the white matter both on T1W and T2W images. Pronounced increased signal of the subcortical white matter on T2WI which tapers toward the ventricle (transmantle sign). The dysplastic cortex appears to be of normal thickness in (A) and (B). In (D), focal thickening of the cortex seems to be present (arrow), probably due to convolution of gyri. Courtesy of dr Norico Salamon. Epileptic Disorders, 2009; 11, 194–205.

Figure 5

Focal cortical dysplasia type Ib associated with dysembryoplastic neuroepithelial tumor (DNET) in a 3-year-old boy by Blumcke IIIb. MR coronal TSE IR TWI (A,B); coronal TSE FLAIR T2WI (C,D) and coronal TSE T2WI (E,F). Histology slides (G,H). Diffuse abnormal hyperintensity of white matter in the right temporal lobe, with blurring of the cortical-white matter junction on T1WI which shows sharper demarcation on T2WI. Within the uncus-amygdala, some locations hypointense on T1WI (white arrow, A) and hyperintense on T2WI (white arrow, C); these proved to be islands of cystic DNET (black arrows, G,H) surrounded by dysplastic cortex. Courtesy of dr Norico Salamon. Epileptic Disorders, 2009; 11, 194–205.

Figure 6

A thirteen-year-old boy with intractable epilepsy. T2 W coronal image (A) shows subtle indistinctness in the gray-white matter differentiation of the right temporal pole suggesting the presence of FCD (long white arrow). PET-MRI co-registration (B) shows obvious hypometabolism (short white arrow) in the right temporal lobe. Courtesy of dr Norico Salamon. Epileptic Disorders, 2009; 11, 194–205.