Imaging distribution and frequency of cortical lesions in patients with multiple sclerosis

Background: The presence of cortical lesions (CLs) and their topographic distribution in the brains of patients with multiple sclerosis (MS) have been clearly shown by recent histopathologic studies. CLs can also be assessed in vivo, with less sensitivity, by using specific MRI sequences. MRI-based lesion probability maps (LPMs) may partially overcome this lack of sensitivity and provide unique information on the spatial distribution and frequency of CLs in MS. Methods: A total of 149 patients with MS (103 relapsing-remitting [RR] and 46 primary progressive [PP]) underwent an MRI examination, which included the double inversion recovery (DIR) sequence for CL assessment. CL masks were then obtained for each patient and a cortical LPM (cLPM) was created for each MS subtype. Results: CLs were mainly distributed in the frontal (RR = 51.8%; PP = 50.5%) and temporal (RR = 30.4%; PP = 35.5%) lobes, with a prominent involvement of the motor (RR = 37.8%; PP = 30.6%) and anterior cingulate (RR = 9.2%; PP = 10.6%) cortices. The extent of brain lobe affected by CLs was higher in RR than in PP patients. The frequency of CL occurrence was higher in PP than in RR patients. Both measurements, however, did not show differences between the 2 MS subtypes at voxel-wise analysis. Conclusions: Patients with RRMS and PPMS share more similarities than differences in terms of CL number, volume, topographic distribution, and frequency. The similarities between histopathologic data and the findings reported here suggest that DIR images can accurately illustrate the focal pathology occurring in the cortical regions of patients with MS, providing clinically relevant information.