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Summary: Ameloblastomas and keratocystic odontogenic tumors (KCOT) are typical jawbone tumors. In addition, dentigerous cysts (DC) and radicular cysts are the most common cystic jawbone lesions, and simple bone cysts (SBC) are the most common jawbone pseudocysts. When these lesions are unilocular, it can be difficult to diagnose them by radiography. In recent years, adding magnetic resonance (MR) imaging to obtain information about soft tissue has been shown to improve the accuracy of jawbone lesion diagnosis. We also have reported MR imaging features of jawbone lesions. However, no systematic method for MR imaging diagnosis of jawbone lesions has been reported. In this review, we examine unilocular lesions such as ameloblastoma, KCOT, adenomatoid odontogenic tumour (AOT), DC, and SBC. First, we describe the MR imaging features of each lesion. Then, we describe our novel MR imaging diagnostic protocol. Using our MR imaging diagnostic protocol to diagnose 31 cases, we obtained a positivity rate of 71.0%. The use of our MR imaging diagnostic protocol for unilocular lesions, which are especially difficult to differentiate by radiography, would improve the morphological and qualitative diagnosis of soft tissue lesions. [ABSTRACT FROM AUTHOR]

Summary: Typical MR images of ameloblastomas on T2-weighted image (WI) or short inversion time inversion-recovery (STIR) show multiple bright high-signal-intensity loci on a high-signal-intensity background. Unilocular cystic-type ameloblastomas show homogeneously bright high signal intensity on T2WI or STIR as a water-like signal intensity. Therefore, it is difficult to distinguish unilocular cystic-type ameloblastoma from other cystic lesions such as keratocystic odontogenic tumors, radicular cysts (residual cysts) and dentigerous cysts only on the basis of MRI signal intensity. In the present study, we evaluated whether contrast-enhanced (CE)-T1WI and dynamic CE-MRI (DCE-MRI) could provide additional information for differential diagnosis in unilocular cystic-type ameloblastoma. Images from 12 cases of suspected unilocular cystic-type ameloblastoma were evaluated in the present study. Of them, 5 had areas suspected of indicating a solid component on T1WI and T2WI (or STIR). Ten had undergone additional CE-T1WI and DCE-MRI. On 5 of 10 cases of CE-T1WI, a tiny enhancement area was detected. On 6 of 10 DCE-images, a time-course enhanced area which was suspected to be a solid component was detected. CE-T1WI was helpful in the diagnosis of ameloblastoma because the tiny enhanced areas were taken to indicate possible solid components. Moreover, the rim-enhancement area on CE-T1WI could be divided into small regions of interest, and some of these showed slightly increased enhancement on DCE-MRI, which was taken to indicate a solid component and/or intramural nodule with focal invasion of ameloblastoma tissue. DCE-MRIs of the four remaining cases, which provided no clues to the diagnosis of ameloblastoma in the manner of the above descriptions, showed thicker rim enhancement than odontogenic cysts. Thus, CE-T1WI and DCE-MRI were helpful in the differential diagnosis of unilocular cystic-type ameloblastomas with homogeneously bright high signal intensity on T2WI or STIR. [ABSTRACT FROM AUTHOR]

Abstract: We retrospectively evaluated magnetic resonance images (MRI) and dynamic contrast-enhanced MRI (DCE-MRI) of ameloblastomas. MRI and DCE-MRI were performed for 10 ameloblastomas. We obtained the following results from the MRI and DCE-MRI. (a) Ameloblastomas can be divided into solid and cystic portions on the basis of MR signal intensities. (b) Ameloblastomas show a predilection for intermediate signal intensity on T1WI, high signal intensity on T2WI, and well enhancement in the solid portion; they also show a homogeneous intermediate signal intensity on T1WI and homogeneous high signal intensity on T2WI, and no enhancement in the cystic portion. (c) The mural nodule or thick wall can be detected in ameloblastomas lesions. (d) CI curves of ameloblastomas show two patterns: the first pattern increases, reaches a plateau at 100–300s, then sustains the plateau or decreases gradually to 600–900s, while the other increases relatively rapidly, reaches a plateau at 90–120s, then decreases relatively rapidly to 300s, and decreases gradually thereafter. There was no difference in the CI curve patterns among primary and recurrent cases, a case with glandular odontogenic tumor in ameloblastoma or among histopathological types such as plexiform, follicular, mixed, desmoplastic, and unicystic type. [Copyright &y& Elsevier]

We evaluated magnetic resonance images (MRI) and the value of dynamic contrast enhanced MRI (DCE-MRI) of pleomorphic adenomas retrospectively. MRI was performed for 18 pleomorphic adenomas, including 11 cases with DCE-MRI. We obtained the following results on the MRI and DCE-MRI. (a) Pleomorphic adenomas showed a predilection for homogeneous intermediate signal intensity on T1-weighted images (T1WI), heterogeneous high signal intensity on T2-weighted images, and heterogeneous enhancement on Gd-T1WI. (b) Of 11 contrast index (CI) curves of pleomorphic adenomas, nine CI curves (81.8%) increased gradually to 600 s or increased gradually, reached a plateau, and sustained the plateau to 600 s. The remaining two (18.2%) increased gradually and decreased gradually thereafter. (c) CI curves reached the maximum CI index at 135–300 s. [Copyright &y& Elsevier]

Introduction: It might be difficult to differentiate solitary bone cysts (SBCs) from other cysts and tumors when the lesion occurs at an unusual location and/or shows atypical radiographic features. Magnetic resonance imaging (MRI) is the most useful modality for evaluating the internal structure of lesions and may have the ability to distinguish SBCs from other lesions. However, few studies exist regarding MRI of SBCs in the oral region. The present study reports on the MR imaging of nine patients with SBCs and describes the diagnostic value of the MRI findings. Materials and methods: Nine patients with SBCs in the mandible were examined using MRI. In all patients, T1- and T2-weighted images (T1-WI, T2-WI) were obtained and contrast enhanced images and dynamic MRI were performed in four cases. Results: MR findings revealed homogeneous intermediate signal intensities (SI) on T1-WI and high SI on T2-WI in all cases. These SI indicated that the SBCs included homogeneous liquid. On the dynamic MRIs in all cases, the SBCs were enhanced from the margin to the inner part, indicating a gradual exudation of the contrast agent from the surrounding medullae to the inner part. These phenomena were not observed on the dynamic MRIs of the other true cysts with epithelial lining. Conclusion: MRI, especially dynamic MRI, can provide useful information for distinguishing SBCs from other cysts or tumors. Furthermore, dynamic MRI findings suggested that the liquid components of SBCs might have infiltrated from the surrounding medullae. [Copyright &y& Elsevier]

Aneurysmal bone cyst (ABC) is a relatively rare, non-neoplastic expansile lesion of bone. Bleeding may occur during an operation or biopsy for ABC, as this cyst is an aneurys with numerous pools of blood. Therefore, it is necessary to diagnose ABC before treatment or biopsy. In the present report, we describe the characteristic computed tomography (CT) and magnetic resonance imaging (MRI) features of ABC in the mandible. Based on the literature and on our own experiences, we compare with the features of ABC with the corresponding features of other lesions showing similar conventional radiographic appearances. In the present case, bone-targeting CT showed the characteristic feature, which reflected the histopathological appearance of a partially cystic meshwork divided by coarse septa. MRI showed almost homogeneous intermediate signal intensity, including a partial slight low-signal-intensity area on the T1-weighted image, and homogeneous high signal intensity, which showed a ‘bubbly’ appearance, on T2-weighted image. On the enhanced T1-weighted image, the intermediate signal intensity areas apart from the areas that showed slight low-signal intensity on the non-enhanced T1-weighted image, were well enhanced. This creates a ‘honeycomb’ appearance. The ‘meshwork’ appearance on bone-targeting CT, the ‘bubbly’ appearance on the T2WI and the ‘honeycomb’ appearance on Gd-T1WI may be the characteristic features of ABC. [Copyright &y& Elsevier]

Abstract: Objectives: To evaluate the diagnostic value of dynamic contrast-enhanced MRI (DCE-MRI) for differentiating between benign and malignant tumors in the palate. Materials and methods: 26 patients with submucosal palatal tumors were preoperatively examined using DCE-MRI. Their maximum contrast index (CImax), time of CImax (Tmax), and washout ratios (WR300 and WR600) were determined from contrast index curves. The submucosal palatal tumors were divided into two groups according to their Tmax values: the early enhancement group (Tmax<300s) consisted of 9 malignant tumors and 6 benign tumors, while the late enhancement group (Tmax≥300s) included one malignant tumor and 10 benign tumors. We compared the following DCE-MRI parameters between the benign and malignant tumors: CImax and Tmax in all cases and CImax, Tmax, and the washout ratios in the early enhancement group. In addition, we performed a regression analysis of the relationships between tumor size and DCE-MRI parameters; i.e., CImax, Tmax, and washout ratios, among the malignant salivary gland tumors and pleomorphic adenomas. Results: In all cases and the early enhancement group, significant differences in Tmax were detected between the benign and malignant tumors (P <0.001 and P <0.05, respectively), and the optimal Tmax cutoff value for differentiating between them was found to be 165s. None of the other parameters displayed significant differences between the benign and malignant tumors. Only the WR600 of the pleomorphic adenomas was significantly correlated with tumor size (R 2 =0.92, P <0.001). Conclusions: Tmax is a useful parameter for distinguishing between benign and malignant submucosal palatal tumors. [Copyright &y& Elsevier]

Abstract: Objective: To evaluate the diagnostic value of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) for minor salivary gland tumors in the oral cavity. Materials and methods: Thirty-two patients with minor salivary gland tumors were examined preoperatively using DCE-MRI. Their maximum contrast index (CImax), time of CImax (Tmax), Tpeak; i.e., the time that corresponded to the CImax×0.90, and washout ratios (WR300 and WR600) were determined from contrast index (CI) curves. We compared these parameters between benign and malignant tumors and among the different histopathological types of minor salivary gland tumors. Then, we categorized the patients’ CI curves into four patterns (gradual increase, rapid increase with high washout ratio, rapid increase with low washout, and flat). Results: Statistically significant differences in Tmax (P =0.004) and Tpeak (P =0.002) were observed between the benign and malignant tumors. Regarding each histopathological tumor type, significant differences in Tmax (P <0.001), Tpeak (P <0.001), and WR600 (P =0.026) were observed between the pleomorphic adenomas and mucoepidermoid carcinomas. It was difficult to distinguish between benign and malignant tumors using our CI curve classification because that two-thirds of the cases were classified into the same type (gradual increase). Conclusion: The DCE-MRI parameters of minor salivary gland tumors contributed little to their differential diagnosis compared with those for major salivary gland tumors. During the diagnosis of minor salivary gland tumors, Tmax is useful for distinguishing between benign and malignant tumors. [Copyright &y& Elsevier]

The radiographical differentiation of adenomatoid odontogenic tumor (AOT) from dentigerous cysts, calcifying odontogenic cysts, calcifying epithelial odontogenic tumors, odontogenic keratocysts and amelobastomas is sometimes difficult. We attempted to differentiate AOT from other lesions similar to AOT in radiographic findings using MRI. The MRI features of AOT in our three cases included homogeneous low SI in the cystic portion and homogeneous intermediate SI in the solid portion on T1WI, homogeneous high SI in the cystic portion and intermediate to slightly high SI in the solid portion on T2WI and enhancement of only the solid portion on CE-T1WI although none of the sequences included SI of calcifications. The contrast index curves in the three cases of AOT showed a gradual increase to 300 s, which signified a benign tumor. These MRI features were characteristic features of AOT and might be a basis for differentiating AOT from the above possible lesions in radiographic examinations. [Copyright &y& Elsevier]