MR of the cerebral operculum: topographic identification and measurement of interopercular distances in healthy infants and children.

PURPOSE To evaluate the role of axial, coronal, and sagittal MR in identification of surface landmarks of the cerebral operculum and to determine the reference values of interopercular distances of each hemisphere in healthy infants and children on MR images.

METHODS Two hundred fourteen cerebral opercula of 35 healthy infants and 72 healthy children were retrospectively evaluated from 107 routine MR brain examinations. The surface landmarks of the operculum and interopercular distances of each hemisphere, which were subjectively divided into anterior interopercular distance (anterior sylvian width) and posterior interopercular distance (posterior sylvian width), were recorded from axial, coronal, and sagittal MR images, respectively. The mean value of anterior interopercular distance of each hemisphere was obtained by averaging two linear measurements of the anterior sylvian width from lateral, sagittal, and axial planes of the same side. Likewise, the posterior interopercular distance of each side of the brain was obtained from averaging of two measurements on lateral, sagittal, and coronal planes.

RESULTS The landmarks of the operculum were best identified by sagittal MR, followed by axial and coronal images. The average values of left anterior interopercular distance, right anterior interopercular distance, left posterior interopercular distance, and right posterior interopercular distance in infants were 1.9 +/- 1.3, 1.6 +/- 1.1, 0.4 +/- 0.7, and 0.2 +/- 0.4 mm, and in children, 0.9 +/- 1.3, 1.0 +/- 1.4, 0.03 +/- 0.23, and 0.01 +/- 0.07 mm, respectively. Infants showed significantly wider interopercular distances than children. Left anterior interopercular distance was significantly wider than right in infants, but not in children. Male children displayed a more significant increase in anterior interopercular distance than did female children. There was no statistic difference in measurements of anterior interopercular distance and posterior interopercular distance between female and male infants.

CONCLUSIONS The operculum should be evaluated with MR in three planes. Infants may show conspicuous sylvian fissures that should not exceed 4.5 mm (mean + 2 SD) anteriorly on axial and sagittal planes and 1.8 mm posteriorly on sagittal and coronal planes. Healthy children who have fully developed opercula should have an anterior interopercular distance of no more than 3.5 mm and a posterior interopercular distance of 0.5 mm.