Anatomic Analysis of the Mastoid Tegmen

Abstract

OBJECTIVES: To examine the dural slope shapes and slope depths in different axes in the mastoid. These are important for surgical guidance. STUDY DESIGN: Setting-Tertiary care otologic center. Patients/materials-105 temporal bone CT scans were used from subjects who had undergone High Resolution Temporal Bone CT scanning for CSOM, using the non-diseased ear scans. In addition, 21 "diseased side" temporal bones were included. INTERVENTIONS: Scans were reconstructed in 3D using Amira software to examine tegmen shapes. The highest and lowest points on the tegmen were measured along 4 axes, 2 in the coronal plane (latero-medial axes posteriorly and anteriorly [L-M ant and L-M post]), and 2 in the sagittal plane (posterio-anterior axes medially and laterally [P-A med and P-A lat]). MAIN OUTCOME MEASURES: The highest and lowest point difference was labeled ΔH. We also measured the height from the superior external canal to the tegmen. RESULTS: There was a unimodal distribution in the ΔH variable for all axes measured. Means and (SD) in mm for ΔH are as follows: L-M post 4.1 (2), L-M ant 2.9 (2.2), P-A med 6.5 (1.9), P-A lat 5.4 (2.2). Tegmen-EAC lat and med height means were 8.4 and 9.7 mm respectively. Representative 3D shapes are presented. CONCLUSION: There appears to be a unimodal distribution of mastoid tegmen shapes and sizes, without clustering into subpopulations. The tegmen slopes have real implications for surgical exploration and disease eradication. A Tegmen classification scheme is presented.