MRI, with thin slice volumetric T1-weighted images, axial and coronal T2-weighted and FLAIR images.
Both images below are from the same patient and illustrate FCD type I, showing regional increase in signal in white matter (which appears brighter) on T2-weighted images, with regional atrophy (compare right temporal, parietal and occipital regions to the same regions on the left)
There is a localized area of cortical thickening, with blurring of the grey-white matter junction and increased signal in the underlying white matter on FLAIR imaging, seen in the left frontal lobe
There is a regional area of gyral expansion in the left inferior frontal lobe, with increased signal in the underlying white matter on T2-weighted imaging (with a central dark core) that is radially-orientated, tapering towards the lateral ventricle (with the 'tail' seen on the second coronal image, arrow). The imaging features FCD type II, can be identical to that of a cortical tuber.
CAUTION in the immature unmyelinated brain, increased T2/FLAIR signal is difficult to identify, as is grey-white matter junction blurring, imaging may need to be repeated after myelination is complete.
CAUTION some focal cortical dysplasias may be difficult to detect, but detection is important as epilepsy surgery can cure intractable seizures that arise from focal cortical dysplasias. Advanced imaging modalities, such as PET and SPECT scans, with expert review, may be required.