 It is caused by lesions in the cortical or subcortical region of the anterior opercular area surrounding the insula forming the gyri of the frontal, temporal, and parietal lobes.The unilateral operculum syndrome is a very rare form of FCMS caused by the formation of unilateral lesions.In this form of FCMS, the unaffected hemisphere of the brain compensates for the unilateral lesion.