Purpose or Case Report: Detection of focal cortical dysplasias (FCDs) can be challenging. Our aim was to evaluate quantitative contrast differences between FCDs and the mirror-location normal gray matter, and the effect thereof on the ease of detection by radiologists.

Methods & Materials: Coronal FLAIR and T1WI of 20 pathology proven cases of FCD, including 11 cases where the diagnosis was missed on the initial review, were analyzed. CNR and conspicuity differences between gray matter within FCDs and contralateral mirror image locations were calculated using manually drawn ROIs. Similar calculations were made in 20 age and gender matched controls for lateralized differences in normal gray matter at locations equivalent to those of FCDs.

Results: On FLAIR images, median (25^th percentile, 75^th percentile) CNR and conspicuity for FCD was 11.3 (8.5, 20.9) and 10.2 (7.1, 15.4), significantly higher than corresponding CNR of 1.0 (-0.2, 5.5) and conspicuity of 0.8 (-0.2, 2.8) for controls (p<0.0001 for both). Similarly, CNR and conspicuity for FCD was also higher than controls on T1WI (p<0.0001). Subgroup analysis showed that these differences from normal were maintained irrespective of FCD detection or lack thereof at the initial review. Median CNR and conspicuity on FLAIR (p = 0.79 and 0.07 respectively) and T1WI (p = 0.64 and 0.76 respectively) were not significantly different for FCD cases that were detected and those that were missed on the initial review.

Conclusions: Focal cortical dysplasia lesions have significantly higher CNR and conspicuity relative to mirror-location gray matter when compared to age and sex matched controls. These differences exist even in cases that were missed at the time of initial review. Accentuation of such differences may serve as a means to improve detection of FCDs.