The parasagittal line: An anatomic landmark for axial imaging

BACKGROUND AND PURPOSE: No validated imaging landmark exists for characteri zing the medial-lateral position of abnormalities at the high convexity-par asagittal region. Our understanding of the courses and deflections of the u pper cerebral sulci is limited. Our purpose, therefore, was to define a fro ntooccipital line with reproducible anatomic relations to the upper cerebra l gyri and sulci and to validate that line for use as an anatomic landmark by specific analysis of the gyral-sulcal relationships along it. METHODS: In 100 subjects of all ages, the gyri and sulci visualized on seri al axial CT sections of the upper brain were traced onto a single flat surf ace to delineate the anatomic relationships among the midline interhemisphe ric fissure, the paramedian superior frontal sulci (SFS) and intraoccipital sulci (IOS), the medial surface sulci, the high convexity sulci, and the i nner table of the skull. These tracings provided a template for drawing a s traight, best-fit parasagittal line from the SFS to the IOS and for assessi ng how reproducibly key anatomic structures align along the parasagittal li ne. To assure the applicability of the line to MR imaging, selected relatio nships were retested on serial axial MR sections in the same subjects. RESULTS: The parasagittal line could be drawn in each case and showed repro ducible alignment with the SFS, hand-motor area, partes marginales, pars de flections, postcentral "parentheses," distal intraparietal sulci, and IOS, In supraventricular sections, the parasagittal line separated the sulci ari sing along the medial surface from those arising along the convexity. CONCLUSION: Because the anatomic relationships of the parasagittal line are reproducible, it may serve as a reference line or landmark. The tendency o f this line to demarcate medial sulci from convexity sulci suggests immedia te application to the definition of vascular territories and vascular water sheds, a topic under active investigation.