Purpose: Some simple bone cysts (SBC) have been reported as “ayyical” or “unusual” because they showed marked bone expansion, radiopaque foci and so on. In this report, We examined whether such radiographic features might be a clue for distinguishing atypical SBCs from typical ones.
Materials and methods: Radiographs of sixty-nine patients with mandibular SBC were reviewed. SBCs with marked mandibular bone expansion or radiopaque foci were classified as “atypical”, and radiographic features were compared with those of typical SBCs on the shape, periphery, internal structure, influence on teeth and surrounding structures, and concurrent lesions in the jaws.
Results: Forty-nine patients were classified as “typical” and 20 as “atypical”. The male to female ratio and the mean age of both groups were 23:26, 19.1 years old and 4:16, 37.6 years old, respectively. Especially, in patients with atypical SBC, the mean age of females was definitely higher than that of patients with typical SBC. The following radiographic features were found to be significantly higher in patients with atypical SBC; that is, scalloped margin, septum, missing lamina dura, involvement of periodontal space, root resorption, displacement of mandibular canal, and concurrent cemento-osseous dysplasia. Preliminary pencil sketch-like margin was found less frequently in atypical SBC.
Conclusion: It was shown that marked mandibular bone expansion and radiopaque foci in the lesion were considered as important radiographic features for distinguishing an atypical SBC.

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Actinomycosis is an unusual chronic suppurative bacterial infection, predominantly caused by Actinomyces israelii, that most often affects the cervico-facial region, accounting for about 60%. Classically, the clinical presentation is a hard, boardlike mass, multiple abscesses and/or sinus tracts, and trismus. Because of the current lack of familiarity with this disease and its ability to mimic other infections or even neoplasms, actinomycosis of the mandible and/or paramandibular tissue may frequently be misdiagnosed. Recently, we experienced three cases with osteomyelitis of the mandible with actinomycosis, clinically diagnosed as a parotid tumor or nonspecific osteomyelitis, however, not conforming radiologically. The images of actinomycotic mandibular osteomyelitis should be, therefore, critically re-evaluated.
Materials and Methods: The CT appearances of two cases with a final diagnosis of actinomycotic mandibular osteomyelitis and nineteen cases diagnosed as non-actinomycotic mandibular osteomyelitis between 1993 and December 2000 were reviewed. The evaluation included bone marrow density changes, sequesta, periosteal reaction, cortical bone thickening, the extent of cortical bone destruction, abscess formation, and soft tissue swelling. Ultrasonography of abscesses from actinomycotic mandibular osteomyelitis was evaluated retrospectively, in two cases (one having received both CT and US examinations). The internal echogenecity of an abscess between the masseter muscle and the ramus of the mandible, and cortical bone destruction were investigated.
Results: On CT, no remarkable osteosclerotic and/or osteolytic bone marrow changes, or small punched out radiolucent areas (less than 6mm) of the mandibular ramus accompanied with a well demarked overlying abscess were seen in actinomycotic osteomyelitis. Any other CT findings in actinomycosis of the mandible were nonspecific. Ultrasonography showed a well-defined hypoehoic area, including multiple, relatively large, hyperechoic spots in abscesses from actinomycotic mandibular osteomyelitis. Destruction of the cortex was also seen simultaneously.
Conclusion: Actinomycotic mandibular osteomyelitis may be characterized by its CT appearances. Ultrasonography can also be used as an additional diagnostic tool to detect those radiological changes caused by actinomycosis.

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In order to demonstrate the utility of the three-dimensional volumetric visualization of subsequent cervical lymph node metastases in patients with tongue carcinoma, a volume rendering visualization system was used. Ten metastatic nodes of 10 patients were found with repeated ultrasonography performed at an interval of at least one month and, if possible, every two weeks. All of the metastatic nodes were detected on CT taken after sonographic examination and were distinctly demonstrated on the volume rendering three-dimensional images obtained with CT data. It is suggested that three-dimensional images reconstructed with CT data provide the accurate anatomical location of non-palpable metastatic nodes detected with repeated ultrasonography.

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It is fundamentally important in surgery to understand the morphology of the surgical field. Three-dimensional CT (3D-CT) images can provide excellent information for maxillofacial surgery. Some computer-navigated systems have already been introduced for neurosurgery and orthopaedic surgery. However, most of them require a fixed operation view and are not suitable for oral and maxillofacial surgery, which requires dynamic views. To address this issue, we are developing a system including an additional image administrator and, in this study, our aim was to establish an inexpensive image navigation system for oral and maxillof acial surgery.
For this purpose, we performed a preliminary computer simulation study to investigate whether 3D-CT images could be successfully overlaid on the surgeon's view.
We used a phantom with an embedded human dried skull as a patient. Acquired CT data were transmitted to a personal computer and reconstructed by a volume rendering method to obtain the navigation images. Subsequently, we transformed these images to virtual reality (VR) movie data in order to freely rotate and magnify them on the display. To reproduce the surgeon's view, we photographed the phantom in the same direction as for 3D-CT images with a digital camera. The VR movies were also created for the surgeon's view. The navigation images were then superimposed on the surgeon's view.
The navigation images could be superimposed on the surgeon's view with sufficient image quality. However, several technical problems need to be solved before this system can be clinically applied.
In conclusion, this system is a potential tool for various oral and maxillofacial surgeries, especially for inexperienced surgeons.

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