title: Magnetic resonance imaging of the temporomandibular joint: diagnostic difficulty caused by extensive pneumatization of the mastoid air cells.
abstract: OBJECTIVE
  During routine MR imaging of temporomandibular joints we have observed that an area of low signal is sometimes identified within the temporal bone overlying the glenoid fossa on proton-density sequences. This finding at times simulates a mass. CT in this situation has demonstrated marked pneumatization of the mastoid air cell extending to that portion of the temporal bone overlying the glenoid fossa. We undertook a clinical study to determine the frequency and appearance of such a finding.
  
  
  METHODS
  We reviewed the images of 12 patients who underwent both MR and CT examinations of their temporomandibular joints. The authors, by consensus, graded all 24 joints using a four-point scale for the presence and appearance of a low-signal area overlying the glenoid fossa on the MR images prior to seeing the corresponding CT images. We then compared our grading with the findings on CT to assess for the presence and extent of pneumatization of the temporal bone overlying the glenoid fossa.
  
  
  RESULTS
  Of the 24 joints reviewed there was identical extent of low signal on MR imaging and extent of pneumatization on CT in 22 of 24 joints. In two of the 24 joints assessed there was overestimation of pneumatization due to extensive sclerosis secondary to surgery.
  
  
  CONCLUSIONS
  The findings of an area of low signal overlying the glenoid fossa on a T2-weighted scan of a nonoperative temporomandibular joint is often due to extensive temporal bone pneumatization of the mastoid air cells. Recognition of the nature of this finding will avoid mistaking it for a fibrous or osseous lesion. Patients with previous operative history may, however, require further investigation with CT.
authors.affiliation: Department of Radiology, Vancouver General Hospital, A Site of Vancouver Hospital and Health Sciences Centre, University of British Columbia, Vancouver, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Wong
authors.forename: P L
authors.initials: PL
authors.lastname: Munk
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D012189:Retrospective Studies; D013704:Temporomandibular Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000473:pathology*; D013705:Temporomandibular Joint Disorders / Q000175:diagnosis* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed