BackgroundFocal cortical dysplasia (FCD) is a condition that often interferes with the cranial mass. Knowledge of focal cortical dysplasia magnetic resonance imaging (MRI) characteristics is of utmost importance for diagnosis. This study aimed to determine the diagnostic contribution of cranial MRI and the apparent diffusion coefficient (ADC) in FCD.ResultsCranial MRI revealed subcortical hyperintensity (SCH) in 52 patients (82.5%), blurring of the gray-white matter (GWM) interface (blurring) in 52 patients (82.5%), cortical thickening (CT) in 48 patients (76%), cortical signal increase (CSI) in 41 patients (65%), and transmantle sign (TMS) in 29 patients (46%). All of the FCDs had a diffusion increase in diffusion-weighted images (DWIs). The mean ADC value at the lesion level was 1.087 × 10−3 mm2/s (0.82/1.316 × 10−3 mm2/s), which was significantly higher than the mean ADC value measured from the contralateral symmetric region (0.758 × 10−3 mm2/s, 0.678/0.872 × 10−3 mm2/s, p = 0.001).ConclusionResults of this study revealed that the most common MRI findings in FCD patients are SCH, blurring, and CT. These findings aid in an easier diagnosis in patients with suspected FCD. All of the lesions studied here in had a diffusion increase in DWI. The quantitative mean ADC values detected in the differential diagnosis of other lesions with a diffusion increase can be used as a reference. Therefore, in addition to the ADC values and electroencephalography (EEG) findings, the conventional MRI findings of FCD, which is resistant to medical treatment, can help to facilitate the diagnosis of FCD, which can be treated with surgery.