Planum Temporale: Morphologic Taxonomy of the Superior Temporal Plane

Abstract

Background: Planum Temporale (PT) is a crucial neuroauditory structure located in the dorsal superior temporal plane (STP) posterior to Heschl’s gyrus (HG). The PT has been implicated in complex auditory function and is well known for its preponderance of leftward asymmetry in normal brains and classic “pie- shaped” morphology. While a majority of cases have easily identifiable PT and HG, there exist some cases in which distinguishability of these two structures is difficult due to morphological variation. The goal of this study is to create a taxonomy of PT morphological features in order to improve the sometimes difficult identification and differentiation of PT from surrounding structures. Methods: A total of 50 (100 hemispheres) healthy intact, high-resolution T1- weighted brain MRIs were obtained from Open Access Series of Imaging Studies (OASIS) and included in this retrospective study. There were 28 women and 22 men, all right-handed. Ages ranged from 18-57 (mean=26.44) years. A 3D cortical surface mesh (grey matter) for each brain was generated using FreeSurfer and manipulated to view the STP using BrainVISA Anatomist neuroimaging software. The PT was isolated from surrounding structures based on pre-defined anatomical criteria and subsequent surface area measurements, linear measurements and qualitative measures were made. Results: A total of four PT configurations were identified: (1) Pie-shaped [45%], (2) Trapezoid-shaped [27%], (3) Rectangular-shaped [19%], and (4) None [9%]. Mean surface areas of measurable PT configurations were: 511.96 mm2 for “Pie-shaped” (n=45), 517.36 mm2 for “Trapezoid-shaped” (n=27) and 472.12mm2 for “Rectangular-shaped” (n=19). The fourth category, “None” (n=9), was not calculable. There were significantly more “Trapezoid-shaped” PTs in females (p<.05). The “None” category occurred significantly more in males (p<.05) and in the right hemisphere (p<.05). Furthermore, the left hemisphere demonstrated significantly greater surface area for “Pie-shaped” PTs (p<.05). Conclusion: We believe that the proposed classifications is the first step in creating a comprehensive taxonomy of the STP. This will aid neuroanatomists, clinicians and students in terms of differentiation of sometimes complex topography of the STP.