The human paracentral lobule, the junction of the precentral and postcentral
gyri at the medial hemispheric surface, contains several important functional
regions, and its variable morphology requires exact morphological and quantitative data. In order to obtain precise data we investigated the morphology of the
paracentral lobule and quantified its visible (extrasulcal) surface. This surface corresponds to commonly used magnetic resonance imaging scout images. We studied 84 hemispheres of adult persons (42 brains; 26 males and 16 females; 20–
–65 years) fixed in neutral formalin for at least 4 weeks. The medial hemispheric
surface was photographed at standard distance and each digital photo was calibrated. Using the intercommissural line system (commissura anterior-commissura posterior or CA-CP line), we performed standardised measurements of the
paracentral lobule. Exact determination of its boundaries and morphological types
was followed by digital morphometry of its extrasulcal surface using AutoCAD
software. We found two distinct morphological types of the human paracentral
lobule: continuous type, which was predominant (95.2%), and rare segmented
type (4.8%). In hemispheres with segmented cingulate sulcus we also found the
short transitional lobulo-limbic gyrus (13.1%). The mean extrasulcal surface of
the left paracentral lobule was significantly larger, both in males (left 6.79 cm2
vs. right 5.76 cm2) and in females (left 6.05 cm2 vs. right 5.16 cm2). However,
even larger average surfaces in males were not significantly different than the
same in females. Reported morphological and quantitative data will be useful
during diagnostics and treatment of pathologies affecting the human paracentral lobule, and in further studies of its cytoarchitectonic and functional parcellations.
