Naoto Ohbayashi

Correlation of darkening of impacted mandibular third molar root on digital panoramic images with cone beam computed tomography findings

OBJECTIVES Darkening of the lower third molar root on panoramic images is known to indicate an intimate relationship between the root and mandibular canal. The objective of this study was to investigate the anatomical relationship between the third molar root and its surrounding structures that leads to this panoramic finding. METHODS Imaging findings of 253 impacted lower third molars examined by both digital panoramic radiography and cone beam CT were reviewed. Panoramic images were evaluated to detect the presence or absence of darkening of the root where the mandibular canal was superimposed. Cone beam CT images were evaluated for the presence or absence of the following two findings: (1) grooving of the root and (2) thinning or perforation of the cortical plate by the root. The correlation between the panoramic and cone beam CT findings was examined using logistic regression analysis. RESULTS 80 (32%) third molars showed a panoramic finding of darkening of the root. Between cone beam CT findings, cortical thinning or perforation alone was significantly correlated with this panoramic finding (80%, P < 0.001). CONCLUSIONS The panoramic finding of mandibular third molar root darkening was considered to reflect cortical thinning or perforation rather than grooving of the root.

MRI of ranulas

Abstract We reviewed the MRI of 20 patients with a ranula (8 simple and 12 plunging) and ten with other cystic masses in the floor of the mouth and/ or suprahyoid portion of the neck (three haemangiomas, two neuromas, one monomorphic adenoma, one lipoma, two lateral cervical cysts and one dermoid cyst). Histological diagnoses were obtained in all cases with the exception of one presumed haemangioma. Ranulas were all well-defined, homogeneous masses giving low signal on T1-and markedly high signal on T2-weighted images. While simple ranulas were all confined to the sublingual space, plunging ranulas were centered on the submandibular space and tended to spill into one or more adjacent spaces. They extended into the sublingual space anteriorly (producung a so-called tail sign) in eight of 12 cases and into the parapharyngeal space superiorly in five. Although they sometimes filled a considerable part of the parapharyngeal space, displacement of surrounding muscles or vessels was usually slight, which was thought to reflect the nature of extravasation pseudocysts. All other cystic masses in our study had one or more MRI finding different from those of ranulas and could be easily differentiated from them.

Diagnostic performance of magnetic resonance imaging for detecting osseous abnormalities of the temporomandibular joint and its correlation with cone beam computed tomography

OBJECTIVE With cone beam CT (CBCT) as the reference standard, the objective of this study was to determine the diagnostic accuracy of MRI for assessing osseous abnormalities of the temporomandibular joint (TMJ). METHODS 106 TMJs from 55 patients with temporomandibular disorder were examined by CBCT and MRI. CBCT images were evaluated by two experienced oral radiologists with regard to the presence or absence of each of the following eight types of osseous abnormalities: Type 1, destructive and erosive osseous changes of the condyle; Type 2, flattening of the articular surface of the condyle; Type 3, deformity of the condyle; Type 4, sclerosis of the condyle; Type 5, osteophyte formation; Type 6, ankylosis; Type 7, erosion of the articular fossa and/or eminence; and Type 8, sclerosis of the articular fossa and/or eminence. For detection of these osseous abnormalities by MRI, proton density-weighted images and T(2) weighted images were evaluated independently by three observers. Using CBCT findings as the reference standard, the diagnostic performance of MRI for detecting various types of osseous abnormalities was evaluated by calculating its sensitivity and specificity. RESULTS Out of 106 joints, CBCT revealed Types 1, 2, 3, 4, 5, 6, 7 and 8 abnormalities in 25, 19, 26, 20, 14, 5, 19 and 22 joints, respectively. The mean sensitivities of MRI among the three observers for detecting Types 1, 2, 3, 4, 5, 6, 7 and 8 abnormalities were 61%, 30%, 82%, 40%, 48%, 34%, 61% and 41%, respectively, whereas the mean specificities were 86%, 92%, 91%, 95%, 84%, 98%, 89% and 91%, respectively. CONCLUSIONS Although high specificity (84-98%) was obtained with MRI, this modality showed relatively low sensitivity (30-82%) for detecting osseous abnormalities of the TMJ. The value of MRI for the detection of TMJ osseous abnormalities is considered to be limited.

Diagnostic accuracy of cone-beam CT in the assessment of mandibular invasion of lower gingival carcinoma: Comparison with conventional panoramic radiography

PURPOSE To evaluate the diagnostic accuracy of cone-beam CT in assessing mandibular invasion by lower gingival carcinoma and compare it with that of panoramic radiography. PATIENTS AND METHODS Fifty patients with squamous cell carcinoma of the lower gingiva who were examined by both panoramic radiography and cone-beam CT before surgery were included in this study. Five radiologists used a 6-point rating scale to independently evaluate cone-beam CT and panoramic images for the presence or absence of alveolar bone and mandibular canal involvement by tumor. Using the histopathogical findings as the gold standard, we calculated and compared the area under the receiver operating characteristic curve (Az value) and the sensitivity and specificity of the two imaging modalities. RESULTS In evaluations of both alveolar bone and mandibular canal involvement, the mean Az value for cone-beam CT (0.918 and 0.977, respectively) was significantly higher than that for panoramic radiography (0.793 and 0.872, respectively). The mean sensitivity for cone-beam CT (89% and 99%, respectively) was significantly higher than that for panoramic radiography (73% and 56%, respectively). There was no significant difference in the mean specificity. While cone-beam CT could provide high-resolution three-dimensional images, the image quality around the alveolar crest was often hampered by severe dental artifacts and image noise, resulting in difficulties in detecting subtle alveolar invasion. CONCLUSION Cone-beam CT was significantly superior to panoramic radiography in evaluating mandibular invasion by lower gingival carcinoma. Its diagnostic value in detecting subtle alveolar invasion, however, may be limited by severe dental artifacts and image noise.

Usefulness of cone beam computed tomography in temporomandibular joints with soft tissue pathology

OBJECTIVE the aim of the study was to evaluate the usefulness of cone beam CT (CBCT) in temporomandibular joints (TMJs) with soft tissue pathology. METHODS 106 TMJs of 55 patients with temporomandibular disorder (TMD) were examined by MRI and CBCT. MR images were used for the evaluation of disc displacement, disc deformity, joint effusion and obscurity of temporal posterior attachment (TPA). CBCT images were evaluated for the presence or absence of osseous abnormalities. The chi(2) test was used to analyse the association between MRI and CBCT findings. RESULTS MRI of 106 TMJs revealed disc displacement, disc deformity, joint effusion and obscurity of the TPA in 68, 73, 28 and 27 joints, respectively. Of the 68 TMJs with disc displacement, anterior disc displacement without reduction (ADDWR) was seen most frequently (47/68). CBCT imaging found 65 TMJs were characterized by the presence of osseous abnormalities and were significantly associated with disc deformity and ADDWR (P < 0.05). There was no statistically significant association between the presence of joint effusion and obscurity of TPA and TMJ osseous abnormalities. CONCLUSIONS TMD patients with confirmed ADDWR or disc deformity on MRI are at risk of having osseous abnormalities in the TMJ and further examination with CBCT is recommended.

MRI characteristics of rheumatoid arthritis in the temporomandibular joint.

OBJECTIVES The aim of this study was to investigate characteristic MRI findings of rheumatoid arthritis (RA) in the temporomandibular joints (TMJs). METHODS 61 patients (122 TMJs) with RA in the TMJ and 50 patients (100 TMJs) with temporomandibular disorder (TMD) were included in this study. MR images of these patients were assessed by two oral radiologists for the presence or absence of osseous changes, disc displacement, joint effusion and synovial proliferation. These findings were compared between the two patient groups. RESULTS Osseous changes in the condyle and articular eminence/fossa in the RA patient group were significantly more frequent than in the TMD patient group, and were often very severe. Joint effusion was also significantly more frequent in the RA patient group. Synovial proliferation was found in all TMJs in the RA patient group, whereas it was very uncommon in the TMD patient group. CONCLUSIONS Severe osseous changes in the condyle and synovial proliferation were considered characteristic MRI findings of RA in the TMJs.

Non-Hodgkin lymphoma involving the mandible: imaging findings

OBJECTIVE The aim of this study was to investigate the imaging findings of non-Hodgkin lymphoma (NHL) involving the mandible. STUDY DESIGN The imaging studies of 4 patients with NHL involving the mandible were retrospectively reviewed. Panoramic and computerized tomographic (CT) images were available for all patients. Magnetic resonance imaging (MRI) was available for 3 patients. RESULTS On panoramic images, an apparent radiolucent lesion was found in only 2 of 4 cases. However, in all cases careful observation demonstrated imaging findings suggesting malignancy. On CT and MRI, tumor replaced the bone marrow in all cases and spread to the surrounding soft tissue in 3 cases. Cortical bone destruction tended to be mild for the extent of tumor involvement. CONCLUSIONS NHL involving the mandible tended to show slight or mild cortical bone destruction relative to the extent of the tumor involvement. Careful observation was considered to be necessary when interpreting conventional images, because they might not clearly demonstrate bone destruction.

Standardization of Thresholding for Binary Conversion of Vocal Tract Modeling in Computed Tomography

Postoperative head and neck cancer patients suffer from speech disorders, which are the result of changes in their vocal tracts. Making a solid vocal tract model and measuring its transmission characteristics will provide one of the most useful tools to resolve the problem. In binary conversion of X-ray computed tomographic (CT) images for vocal tract reconstruction, nonobjective methods have been used by many researchers. We hypothesized that a standardized vocal tract model could be reconstructed by adopting the Hounsfield number of fat tissue as a criterion for thresholding of binary conversion, because its Hounsfield number is the nearest to air in the human body. The purpose of this study was to establish a new standardized method for binary conversion in reconstructing three-dimensional (3-D) vocal tract models. CT images for postoperative diagnosis were secondarily obtained from a CT scanner. Each patients minimum settings of Hounsfield number for the buccal fat-pad regions were measured. Thresholds were set every 50 Hounsfield units (HU) from the bottom line of the buccal fat-pad region to -1024 HU, the images were converted into binary values, and were evaluated according to the three-grade system based on anatomically defined criteria. The optimal threshold between tissue and air was determined by nonlinear multiple regression analyses. Each patients minimum settings of the buccal fat-pad regions were obtained. The optimal threshold was determined to be -165 HU from each patients minimum settings of the Hounsfield number for the buccal fat-pad regions. To conclude, a method of 3-D standardized vocal tract modeling was established.

Ultrasonographic Assessment of New Bone Formation in Maxillary Distraction Osteogenesis

p ince McCarthy first applied it to the mandible, disraction osteogenesis (DOG) has become a popular echnique to stimulate new bone formation in paients with severe craniomaxillofacial deformities. Afer DOG, new bone formation can be monitored by eans of clinical observation, plain radiography, ual-energy x-ray absorptiometry, computed tomogaphy (CT), and ultrasonography (US). lain radiography is used at each phase of the distracion protocol, but the 2-dimensional images do not rovide sufficient information on which to allow asessment of the early stages of osteogenesis or the evelopment of callus. CT is more precise and ffective for assessing new bone formation compared ith plain radiography; however, issues of inconenience, cost, and radiation exposure make it diffiult to recommend serial CT scans.

Morphological observation of the medial pterygoid muscle by the superimposition of images obtained by lateral cephalogram and MRI

Objective To observe the morphological relationship between the maxillofacial skeleton and medial pterygoid muscle by superimposing images constructed by MRI on a cephalogram. Design Cross-sectional study. Setting The Departments of Maxillofacial Orthognathics and Orthodontics, Tokyo Medical and Dental University. Participants Sixteen patients (5 males and 11 females, aged between 13.5 and 27.5 years) with various craniofacial skeletal patterns, who were about to start orthodontic treatment. Methods Lateral cephalometric radiographs and MRI scans were obtained and their images uploaded to a computer using a digitizer. The area of the medial pterygoid muscle was selected by binarization from the MRI. The mid-sagittal-plane MRI with a complete superimposed sagittal image of the medial pterygoid muscle was superimposed on the cephalogram using anatomical structures situated in the mid-sagittal plane of the head and shapes that could be identified from both the radiograph and the MRI image. Results These combined images showed various shapes of the medial pterygoid muscle. The inclination axis of the medial pterygoid muscle was correlated with various cephalometric variables including SNB (r=0.658), Facial angle (r=0.601), ramus inclination (r=0.676) and Ba-Po% (r=0.585). The volume of the medial pterygoid muscle was also correlated with cephalometric variables such as ramus inclination (r=0.453), Ba-Nmm (r=0.676), Ba-Po% (depth) (r=0.447), Ar-Go% (depth) (r=0.444) and Ar-Go% (actual length) (r=0.532). Conclusions Morphometric analysis using a superimposed image of the medial pterygoid muscle produced from a cephalogram and MRI may help explain the influence of the medial pterygoid muscle inclination axis and volume on the shape of the mandibular bone, especially the shape of the ramus.