Cerebrospinal fluid cleft with cortical dimple: MR imaging marker for focal cortical dysgenesis

PURPOSE: To determine whether the magnetic resonance (MR) imaging feature of a cerebrospinal fluid (CSF) cleft and cortical dimple can be used as a marker for cortical dysgenesis. MATERIALS AND METHODS: MR images in 875 patients with epilepsy were evaluated for the following features of focal cortical dysgenesis: cortical thickening, indistinct junction between gray and white matter, macrogyria, and abnormal sulcal pattern. Images with these features were reevaluated to determine the relationship between the CSF cleft-cortical dimple complex and focal cortical dysgenesis and its contribution to diagnosis. The cleft-dimple complex was defined as a prominent CSF space associated with a region of cortical volume loss adjacent to the dysgenesis. RESULTS: Seventy-one patients had cortical dysgenesis, including 27 with cellular proliferation abnormalities, 18 with migration abnormalities, 25 with cortical organization abnormalities, and one with miscellaneous anomalies. Histologic correlation was available in 20 patients. There was an associated cortical dimple in 29 (41%) patients. This association was strongest in patients with cortical organization abnormalities: It was present in 22 of the 25 (88%) patients. In 12 (48%) patients with abnormalities of cortical organization, the CSF cleft was easier to detect than other features of cortical dysgenesis or contributed directly to the MR imaging diagnosis. CONCLUSION: The cleft-dimple complex is a marker for subtle cases of focal cortical dysgenesis and may be due to maldevelopment. In patients with seizures, the presence of a cleft-dimple complex should alert the physician to scrutinize adjacent regions for developmental anomalies.