Focal cortical dysplasia: Appearance of MR images

PURPOSE: To clarify the magnetic resonance (MR) imaging characteristics of focal cortical dysplasia (FCD). MATERIALS AND METHODS: The authors reviewed the MR images of 14 patients with FCD, which was confirmed with histologic examination. RESULTS: MR images exhibited FCD in 13 of the 14 patients. All lesions were localized to part of one hemisphere. T2-weighted images showed blurring of the gray matter-white matter junction and abnormal signal intensity in the white matter in 11 patients. T1-weighted images showed blurring of the gray matter-white matter junction in seven patients, broad gyri in nine, thick cortices in nine, abnormal sulci in 10, and focal enlargement of the overlying subarachnoid space or adjacent ventricle in eight. Surgical specimens exhibited disruption of cortical lamination without abnormal gyration in all patients, cytomegalic neurons in the cortex in three, disorganized bizarre glial cells in the cortex in seven, ectopic neurons or bizarre glial cells in the white matter in nine, and blurring of the gray matter-white matter junction in one. CONCLUSION: Blurring of the gray matter-white matter junction with abnormal signal intensity in the white matter on T2-weighted images is characteristic of FCD. The presence of ectopic neurons and bizarre glial cells, dysmyelination, and a reduction in the number of myelinated fibers might have been responsible for the MR imaging characteristics.