Cystic lesions of the maxillomandibular region: MR imaging distinction of odontogenic keratocysts and ameloblastomas from other cysts.

OBJECTIVE: Differentiating odontogenic keratocysts and ameloblastomas from other cystic lesions in the maxillomandibular region is important because of their high recurrence rates. Conventional radiography, CT, and fine-needle aspiration biopsy are limited for differential diagnosis. The purpose of this study was to review the MR findings in patients with odontogenic keratocysts, ameloblastomas, and other maxillomandibular cysts to determine the value of MR imaging in the differential diagnosis of these lesions. SUBJECTS AND METHODS: MR images were obtained in 38 patients with 43 cystic lesions of the maxillomandibular region. All the lesions (19 odontogenic keratocysts, 11 ameloblastomas, five primordial cysts, five radicular cysts, and three cysts of other types) were pathologically confirmed by surgery or biopsy. Contrast-enhanced MR studies were performed in 34 patients. Images were reviewed to determine various imaging parameters: locularity, solid or cystic pattern, thickness and contrast enhancement of the walls, and homogeneity and signal intensities of the fluids. T2 relaxation times of cystic components were calculated in 31 lesions.
RESULTS: MR images of odontogenic keratocysts showed that the cyst were unilocular in 10 lesions and multilocular in nine. In 10 lesions the cysts wall was uniformly thin and had poor contrast enhancement. Seven cysts had thick walls and two had no definite walls. In 17 lesions, the cystic contents showed heterogeneous signal intensity on T1-weighted images, T2-weighted images, or both. Eight cysts had predominantly intermediate or high T1-weighted signal intensity, and six cysts had predominantly intermediate T2-weighted signal intensity. MR findings in ameloblastomas were different from those in odontogenic keratocysts: a mixed solid and cystic pattern (11 lesions), irregularly thick walls (11 lesions), papillary projections (seven lesions), and strong enhancement of solid components (nine lesions). T2 relaxation times of cystic components were significantly shorter in odontogenic keratocysts than in ameloblastomas, with no overlap. All other cysts showed a unilocular, purely cystic pattern, with homogeneous fluids, although the T2 relaxation times of four lesions overlapped those of odontogenic keratocysts.
CONCLUSION: From the MR findings of the walls, solid components, and the fluid contents, odontogenic keratocysts could be differentiated from ameloblastomas in all cases, although some other cysts showed MR findings similar to those of odontogenic keratocysts.