Korean J Radiol.  2018 Feb;19(1):79-84. 10.3348/kjr.2018.19.1.79.

Diffusion-Weighted MR Imaging of Unicystic Odontogenic Tumors for Differentiation of Unicystic Ameloblastomas from Keratocystic Odontogenic Tumors

• Han Y
• Fan X
• Su L
• Wang Z

• KMID: 2425112
• DOI: http://doi.org/10.3348/kjr.2018.19.1.79

Abstract

OBJECTIVE
Differentiating unicystic ameloblastomas from keratocystic odontogenic tumors (KCOT) is necessary for the planning of different treatment strategies; however, it is difficult based on conventional CT and MR sequences alone. The purpose of this study was to investigate the utility of diffusion-weighted imaging (DWI) and apparent diffusion coefficients (ADCs) in the differentiation of the two tumors.
MATERIALS AND METHODS
We prospectively studied 40 patients with odontogenic cysts and tumors of the maxillomandibular region using conventional MR imaging and DWI. ADCs were measured using 2 b factors (500 and 1000).
RESULTS
Unicystic ameloblastomas (n = 11) showed free diffusion on DWI and a mean ADC value of 2.309 ± 0.17 × 10-3 mm2/s. KCOT (n = 15) showed restricted diffusion on DWI with a mean ADC value of 0.923 ± 0.20 × 10-3 mm2/s. The ADC values of unicystic ameloblastomas were significantly higher than those of KCOT (p < 0.001, Mann-Whitney U-test). An ADC cut-off value of 2.0 × 10-3 mm2/s to differentiate KCOT and unicystic ameloblastomas resulted in a 100% sensitivity and 100% specificity. Dentigerous cysts (n = 3) showed restricted diffusion on DWI and similar ADC values (1.257 ± 0.05 × 10-3 mm2/s) to those of KCOT.
CONCLUSION
Diffusion-weighted imaging and ADC determination can be used as an adjuvant tool to differentiate between unicystic ameloblastomas and KCOT, although the ADC values of dentigerous cysts overlap with those of KCOT.

Keyword

Diffusion-weighted MR imaging; DWI; Unicystic ameloblastomas; Keratocystic odontogenic tumors; Apparent diffusion coefficients; ADC

MeSH Terms

Ameloblastoma*
Dentigerous Cyst
Diffusion
Humans
Magnetic Resonance Imaging*
Odontogenic Cysts*
Odontogenic Tumors*
Prospective Studies
Sensitivity and Specificity

Figure

• 

  Fig. 1 12-year-old male patient with unicystic ameloblastoma at left mandibular region.A. Axial contrast-enhanced T1-weighted image shows unilocular cystic lesion (arrow) with rim enhancement. B. Axial fat-suppressed T2-weighted image shows lesion (arrow) with high signal intensity. C. Diffusion-weighted image at b = 1000 s/mm2 shows loss of signal within lesion (arrow).D. Axial color ADC map shows lesion (arrow) with high ADC (2.013 × 10-3 mm2/s). ADC = apparent diffusion coefficient

• 

  Fig. 2 25-year-old male patient with keratocystic odontogenic tumors at right mandibular region.A. Axial contrast-enhanced T1-weighted image shows unilocular cystic lesion (arrow) with rim enhancement in mandibular ramus. B. Axial fat-suppressed T2-weighted image shows lesion (arrow) with high signal intensity. C. Diffusion-weighted image at b = 1000 s/mm2 shows that lesion has retained signal (arrow). D. Axial color ADC map shows lesion (arrow) with low ADC (1.02 × 103 mm2/s).

• 

  Fig. 3 Box-and-whisker plot for comparing apparent diffusion coefficient values of unicystic ameloblastomas, KCOT and dentigerous cysts. p, Mann-Whitney U test.Bottom and top of each box and whisker plot are first and third quartiles, and band inside box is second quartile. Ends of whiskers represent minimum and maximum of all data. All data are included between whiskers. KCOT = keratocystic odontogenic tumors

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