title: Anatomic analysis of the mastoid tegmen: slopes and tegmen shape variances.
abstract: OBJECTIVE
  To examine the dural slope shapes and slope depths in different axes in the mastoid. These are important for surgical guidance.
  
  
  METHODS
  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.
  
  
  METHODS
  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]).
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Otolaryngology, Department of Surgery, Dalhousie University, Halifax, Nova Scotia.
authors.forename: Fawaz M
authors.initials: FM
authors.lastname: Makki
authors.forename: Hosam A
authors.initials: HA
authors.lastname: Amoodi
authors.forename: Rene G
authors.initials: RG
authors.lastname: van Wijhe
authors.forename: Manohar
authors.initials: M
authors.lastname: Bance
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008416:Mastoid / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011859:Radiography; D013701:Temporal Bone / Q000033:anatomy & histology* / Q000000981:diagnostic imaging