title: Diffusion-weighted imaging in the evaluation of odontogenic cysts and tumours.
abstract: OBJECTIVE
  The differentiation between keratocystic odontogenic tumour (KCOT) and other cystic/predominantly cystic odontogenic tumours is difficult on conventional CT and MR sequences as there is overlap in the imaging characteristics of these lesions. The purpose of this study was to evaluate the role of diffusion-weighted imaging (DWI) and to assess the performance of apparent diffusion coefficients (ADCs) in the differential diagnosis of odontogenic cysts and tumours.
  
  
  METHODS
  20 patients with odontogenic cysts and tumours of the maxillomandibular region were examined with DWI. Diffusion-weighted images were obtained with a single-shot echoplanar technique with b-values of 0, 500 and 1000 s mm(-2). An ADC map was obtained at each slice position.
  
  
  RESULTS
  The cystic areas of ameloblastoma (n=10) showed free diffusion with a mean ADC value of 2.192±0.33×10(-3) mm(2) s(-1), whereas the solid areas showed restricted diffusion with a mean ADC value of 1.041±0.41×10(-3) mm(2) s(-1). KCOT (n=5) showed restricted diffusion with a mean ADC value of 1.019±0.07×10(-3) mm(2) s(-1). There was a significant difference between the ADC values of KCOT and cystic ameloblastoma (p<0.01, Mann-Whitney U-test). The cut-off with which KCOT and predominantly cystic ameloblastomas were optimally differentiated was 2.013×10(-3) mm(2) s(-1), which yielded 100% sensitivity and 100% specificity.
  
  
  CONCLUSIONS
  DWI can be used to differentiate KCOT from cystic (or predominantly cystic) odontogenic tumours.
authors.affiliation: Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India.
authors.forename: K
authors.initials: K
authors.lastname: Srinivasan
authors.forename: A
authors.initials: A
authors.lastname: Seith Bhalla
authors.forename: R
authors.initials: R
authors.lastname: Sharma
authors.forename: A
authors.initials: A
authors.lastname: Kumar
authors.forename: A
authors.initials: A
authors.lastname: Roychoudhury
authors.forename: O
authors.initials: O
authors.lastname: Bhutia
mesh_terms: D000328:Adult; D000564:Ameloblastoma / Q000175:diagnosis*; D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007573:Jaw Neoplasms / Q000175:diagnosis*; D008297:Male; D008336:Mandibular Diseases / Q000175:diagnosis*; D009807:Odontogenic Cysts / Q000175:diagnosis*; D011446:Prospective Studies; D055815:Young Adult