Diffusion-weighted MR imaging of ameloblastomas and keratocystic odontogenic tumors: differentiation by apparent diffusion coefficients of cystic lesions.

BACKGROUND AND PURPOSE Ameloblastomas and keratocystic odontogenic tumors are major aggressive odontogenic tumors in the maxillomandibular regions, but the differentiation between these 2 tumors is frequently ineffective based on only conventional CT and MR imaging findings. Here, we evaluated diffusion-weighted MR imaging for the differentiation of these 2 odontogenic tumors. MATERIALS AND METHODS We prospectively studied 9 patients with ameloblastoma and 7 patients with keratocystic odontogenic tumor using diffusion-weighted MR imaging. Apparent diffusion coefficients (ADCs) of the nonenhancing and solid lesions in these tumors were determined with use of 2 b factors (500 and 1000). RESULTS Two types of nonenhancing lesions were identified; one with high signal intensity on fat-suppressed T2-weighted images (type A) and the other with low or intermediate intensity (type B). The type A nonenhancing lesions were observed in all the ameloblastomas, but they were evident in only 2 keratocystic odontogenic tumors. It is interesting to note that the ADCs of the nonenhancing lesions in the ameloblastomas were significantly higher than those of the nonenhancing lesions in the keratocystic odontogenic tumors (2.48 +/- 0.20 x 10(-3) mm(2)/s vs 1.13 +/- 0.56 x 10(-3) mm(2)/s; P < .001). The ADCs of the solid lesions in the ameloblastomas (1.39 +/- 0.15 x 10(-3) mm(2)/s) were significantly lower than those of the nonenhancing lesions in the ameloblastomas and were similar to those of the nonenhancing lesions in the keratocystic odontogenic tumors. CONCLUSION ADC determination may be used as an adjunct tool for differentiation between ameloblastomas and keratocystic odontogenic tumors.