Usefulness of Simple Diffusion Kurtosis Imaging for Head and Neck Tumors: An Early Clinical Study.

Diffusion kurtosis (DK) imaging (DKI), a type of restricted diffusion-weighted imaging, has been reported to be useful for tumor diagnoses in clinical studies. We developed a software program to simultaneously create DK images with apparent diffusion coefficient (ADC) maps and conducted an initial clinical study. Multi-shot echo-planar diffusion-weighted images were obtained at b-values of 0, 400, and 800 sec/mm2 for simple DKI, and DK images were created simultaneously with the ADC map. The usefulness of the DK image and ADC map was evaluated using a pixel analysis of all pixels and a median analysis of the pixels of each case. Tumor and normal tissues differed significantly in both pixel and median analyses. In the pixel analysis, the area under the curve was 0.64 for the mean kurtosis (MK) value and 0.77 for the ADC value. In the median analysis, the MK value was 0.74, and the ADC value was 0.75. The MK and ADC values correlated moderately in the pixel analysis and strongly in the median analysis. Our simple DKI system created DK images simultaneously with ADC maps, and the obtained MK and ADC values were useful for differentiating head and neck tumors from normal tissue.

Imaging characteristics of incidentally detected cosmetic surgery-derived foreign bodies on CT images in the maxillofacial region.

OBJECTIVES: This study examined the imaging characteristics of cosmetic surgery-derived foreign bodies in the maxillofacial region through a retrospective review of cosmetic material foreign bodies incidentally detected on computed tomography (CT) images in routine clinical practice. METHODS: We retrospectively investigated cases of cosmetic surgery-derived foreign bodies other than dental materials in the maxillofacial region, using 5 years of CT image data stored on an imaging server. The imaging findings of these foreign bodies were investigated, along with patient age, patient sex, whether the foreign bodies were associated with the disease targeted by the CT scan, and the availability of cosmetic surgery information prior to examination. RESULTS: Foreign bodies were more common in women (19/21 cases), and affected patients displayed a wide age range (20-84 years). Four types of cosmetic surgery-derived foreign bodies in the maxillofacial region were detected by CT examination: nasal prostheses (nasal region), lifting sutures and injectable facial fillers (both in the buccal region), and silicone chin implants (chin region). CONCLUSIONS: A cosmetic surgery-derived foreign body should be suspected when a foreign body is identified without a dental source of infection. In addition, cosmetic surgery-derived foreign bodies may be present in numerous patients, regardless of age or sex.

In vitro assessment of factors affecting the apparent diffusion coefficient of Jurkat cells using bio-phantoms.

It is well known that many tumor tissues show lower apparent diffusion coefficient (ADC) values, and that several factors are involved in the reduction of ADC values. The aim of this study was to clarify how much each factor contributes to decreases in ADC values. We investigate the roles of cell density, extracellular space, intracellular factors, apoptosis and necrosis in ADC values using bio-phantoms. The ADC values of bio-phantoms, in which Jurkat cells were encapsulated by gellan gum, were measured by a 1.5-Tesla magnetic resonance imaging device with constant diffusion time of 30sec. Heating at 42℃ was used to induce apoptosis while heating at 48℃ was used to induce necrosis. Cell death after heating was evaluated by flow cytometric analysis and electron microscopy. The ADC values of bio-phantoms including non-heated cells decreased linearly with increases in cell density, and showed a steep decline when the distance between cells became less than 3µm. The analysis of ADC values of cells after destruction of cellular structures by sonication suggested that approximately two-thirds of the ADC values of cells originate from their cellular structures. The ADC values of bio-phantoms including necrotic cells increased while those including apoptotic cells decreased. This study quantitatively clarified the role of the cellular factors and the extracellular space in determining the ADC values produced by tumor cells. The intermediate diffusion time of 30msec might be optimal to distinguish between apoptosis and necrosis.

Ultrasound procedure for the diagnosis of mass lesions in the oral region.

OBJECTIVES: To examine the diagnostic usefulness and procedures of ultrasonography (US) for mass lesions in the soft tissue of the oral region. METHODS: This study involved patients with mass lesions (tumorous lesions and cysts) who had undergone US and histopathological examinations from January 2017 to December 2019. The following points were evaluated by two observers using an evaluation scale: vascularity, echo intensity level, boundary, margin shape, distribution of internal echoes, and capsule. The usefulness of each point for differential diagnosis of tumorous lesions and cysts was statistically analyzed. RESULTS: Forty-five mass lesions in the soft tissue of the oral region (33 tumorous lesions and 12 cysts) were analyzed. There were significant differences in four evaluation points between the tumorous lesions and cysts: vascularity, echo intensity level, boundary, and margin shape. Cysts were almost completely excluded diagnostically, especially when vascularity was observed. There were also significant differences in two evaluation points between nonvascular tumorous lesions and cysts: echo intensity level and boundary. CONCLUSIONS: In US examination for mass lesions in the oral region, it was possible to diagnose tumorous lesions and exclude cysts when vascularity was observed. When vascularity was not observed, however, tumorous lesions and cysts could be identified using two evaluation points: echo intensity level and boundary.

An imaging­based diagnostic approach to vascular anomalies of the oral and maxillofacial region.

The accurate diagnosis of vascular anomalies (VAs) is considered a challenging endeavor. Misdiagnosis of VAs can lead clinicians in the wrong direction, such as the performance of an unnecessary biopsy or inappropriate surgical procedures, which can potentially lead to unforeseen consequences and increase the risk of patient injury. The purpose of the present study was to develop an approach for the diagnosis of VAs of the oral and maxillofacial region based on computed tomography (CT), magnetic resonance imaging (MRI) and dynamic contrast-enhanced MRI (DCE-MRI). In the present study, the CT and MR images of 87 VAs were examined, and the following imaging features were evaluated: Detectability of the lesion, the periphery of the lesion, the inner nature of the lesion, the density of the lesion on CT, the signal intensity of the lesion on MRI, the detectability of phleboliths and the shape of the lesion. A total of 29 lesions were further evaluated using the contrast index (CI) curves created from the DCE-MRI images. A diagnostic diagram, which is based on the imaging features of VAs and CI curve patterns, was subsequently extrapolated. The results obtained demonstrated that the VAs were detected more readily by MRI compared with CT, whereas the detectability of phleboliths was superior when using CT compared with MRI. VAs showed a propensity for homogeneous isodensity on CT, whereas, by contrast, they exhibited a propensity for heterogeneous hyperdensity on CE-CT. VAs also showed a propensity for homogeneous intermediate signal intensity when performing T1-weighted imaging (T1WI), heterogeneous high signal intensity when performing short tau inversion recovery MRI, and heterogeneous high signal intensity when performing fat-saturated CE-T1WI. The CI curves of VAs were found to exhibit a specific pattern: Of the 29 CI curves, 23 (79.3%) showed early weak enhancement, followed by a plateau leading up to 400-600 sec. An imaging-based diagnostic diagram was ultimately formulated. This diagram can act as an aid for radiologists when they are expecting to find a VA, and hopefully serve the purpose of simplifying the diagnostic process. Taken together, the findings of the present study indicated that DCE-MRI may be considered a useful tool for the diagnosis of VAs.

Characteristic Mean Kurtosis Values in Simple Diffusion Kurtosis Imaging of Dentigerous Cysts.

We evaluated the usefulness of simple diffusion kurtosis (SD) imaging, which was developed to generate diffusion kurtosis images simultaneously with an apparent diffusion coefficient (ADC) map for 27 cystic disease lesions in the head and neck region. The mean kurtosis (MK) and ADC values were calculated for the cystic space. The MK values were dentigerous cyst (DC): 0.74, odontogenic keratocyst (OKC): 0.86, ranula (R): 0.13, and mucous cyst (M): 0, and the ADC values were DC: 1364 × 10-6 mm2/s, OKC: 925 × 10-6 mm2/s, R: 2718 × 10-6 mm2/s, and M: 2686 × 10-6 mm2/s. The MK values of DC and OKC were significantly higher than those of R and M, whereas their ADC values were significantly lower. One reason for the characteristic signal values in diffusion-weighted images of DC may be related to content components such as fibrous tissue and exudate cells. When imaging cystic disease in the head and neck region using SD imaging, the maximum b-value setting at the time of imaging should be limited to approximately 1200 s/mm2 for accurate MK value calculation. This study is the first to show that the MK values of DC are characteristically higher than those of other cysts.

Bone quality and quantity of the anterior maxillary trabecular bone in dental implant sites.

OBJECTIVES: The aim of this study was to investigate the characteristics of implant sites on the edentulous alveolar ridge in the anterior maxilla. We studied the bone quantity and quality of implant sites at the anterior maxilla using CT images for the 33 implant sites on patients who underwent dental implant therapy in our Department since 2006. MATERIALS AND METHODS: Computed tomography (CT) images of 33 patients (20 women: 13 men) encompassing 33 implant sites were chosen and examined. The recipient sites for implant placement were determined based on CT data using an implant planning software (Simplant 11.0). The mean bone density values in Hounsfield unit (HU) were recorded using Simplant for both the simulated implant areas and the trabecular bone width. We classified the edentulous alveolar ridge and bone quality according to a classification based on Lekholm and Zarb (1985). RESULTS: Incisors had higher bone densities than canines. Women had lower bone densities than men. Canines displayed greater trabecular bone density and alveolar bone widths than incisors. No maxillary sites were judged to have a bone quality of 1 in this group. Quality 3 accounted for 69.7% of the total samples. CONCLUSIONS: An assessment of bone quality in the anterior alveolar ridge may well reflect age-related systemic pathological conditions and should be used in dental implant treatment planning to avoid associated risk factors.

Test-retest reliability of MRI-based disk position diagnosis of the temporomandibular joint.

This study evaluated the test-retest reliability for determining the temporomandibular joint (TMJ) disk position, diagnosed using magnetic resonance imaging (MRI). These assessments were done as a base-line measurement for a prospective cohort study, which examines the risk factors for precipitation and progression of temporomandibular disorders. Fifteen subjects (mean age, 24.2 ± 0.94 years; male/female = 8/7) were recruited from the students of Okayama University Dental School. Sagittal MR TMJ images were taken with a 1.5-T MR scanner (Magneton Vision, Siemens) in close and maximal open positions twice at about 1-week (6-11 days) interval. The images were displayed using 200% magnification on a computer screen with a commercially available image software package (OSIRIS, UIN/HCUG). Three calibrated examiners diagnosed the disk positions using the standardized criteria. The disk position of each joint was classified as normal, anterior disk displacement with or without reduction, and others. The first and second disk position diagnoses were compared, and the test-retest reliability level was calculated using the kappa index. The second disk position diagnosis was consistent with the first in 27 out of 30 joints. The calculated kappa value representing the test-retest reliability level between the first and second disk position diagnosis was 0.812. These results indicated that the test-retest reliability of MRI-based diagnosis of TMJ disk positions at about 1-week interval was substantially high, even though they were not completely consistent.

Collision tumor of small cell carcinoma and squamous cell carcinoma of the maxillary sinus: Case report.

A collision tumor refers to the coexistence of two diagnostically distinct tumors in a common anatomic space. Collision tumors are rare in the oral and maxillofacial region. The present study reported on the case of an 82-year-old female with a collision tumor in the maxillary sinus consisting of small cell carcinoma (SmCC) and squamous cell carcinoma (SCC). Computed tomography (CT) imaging revealed a mass in the right maxillary sinus. The lesion exhibited heterogeneous low signal intensity (SI) on T1-weighted imaging (T1WI), high SI on short T1 inversion recovery and heterogeneous solid enhancement on contrast-enhanced T1WI. The histopathology result of a biopsy specimen confirmed SmCC. After the patient received a course of chemoradiotherapy, follow-up CT revealed a residual tumor. In a second surgery, a remaining tumor and histopathology revealed SCC with no evidence of SmCC. The final diagnosis was a collision tumor made up of SCC and SmCC.

Influence of mesiodens on adjacent teeth and the timing of its safe removal.

Purpose: To focus on the effects of the presence of mesiodens on adjacent teeth and to investigate the timing of its safe removal. Materials and Methods: Cone-beam computed tomography examinations, obtained at Okayama University Hospital over a three-year period, were inspected. Data were recorded including the number of mesiodens; associated abnormalities; and the relationship with neighboring structures. Depending on multiple factors, the risk of developing complications due to early extraction of a mesiodens was divided into three categories: high, medium, and low risk. Results: A total of 5,958 cone-beam computed tomography exams were obtained, 460 patients aged 3-85 years were diagnosed with a total of 568 mesiodens, 382 (67.3%) of which were discovered in young patients (age <10 years), and 333 (87.2%) of these were associated with abnormalities. Regarding the risk categories, 11 (1.9%) were considered to be in the high-risk, five (0.9%) in the medium-risk and 552 (97.2%) in the low-risk categories. Moreover, eight out of 11 high-risk mesiodens were extracted and no post-operative complications have been seen. Conclusion: As the results showed that no postoperative complications were seen in all the extracted cases of high-risk mesiodens, this indicates the possibility of safe extraction at an early age which could reduce related future complications.

Corticomotor plasticity induced by tongue-task training in humans: a longitudinal fMRI study.

Corticomotor pathways may undergo neuroplastic changes in response to acquisition of new motor skills. Little is known about the motor control strategies for learning new tongue tasks. The aim of this study was to investigate the longitudinal effect of novel tongue-task training on corticomotor neuroplasticity. Thirteen healthy, right-handed men, aged 24-35 years (mean age ± SD: 27.3 ± 0.3 years), performed a training task consisting of standardized tongue protrusion onto a force transducer. The tongue task consisted of a relax-protrude-hold-relax cycle with 1.0 N as the target at the hold phase lasting for 1.5 s. Subjects repeated this task for 1 h. Functional magnetic resonance imaging was carried out before the tongue-task training (baseline), 1-h after the training, and one-day and one-week follow-up. During scanning, the subjects performed tongue protrusion in blocks interspersed with rest. A region-of-interest (ROI) approach and an explorative search were implemented for the analysis of corticomotor activity across conditions. All subjects completed the tongue-task training (mean success rate 43.0 ± 13.2%). In the baseline condition, tongue protrusion resulted in bilateral activity in regions most typically associated with a motor task including medial frontal gyrus (supplementary motor area [SMA]), precentral gyrus (tongue motor cortex), putamen, thalamus, and cerebellum. The ROI analysis revealed increased activity in the precentral gyrus already 1 h post-training. One day after the training, increased activity was observed in the precentral gyrus, SMA, putamen, and cerebellum. No increase was found 1 week after training. Correlation analyses between changes in success rates and changes in the numbers of voxels showed robust associations for left Area 4a in primary motor cortex 1 h, 1 day, and 1 week after the tongue-task training and for the left Area 4p in primary motor cortex and the left lateral premotor cortex 1 day after the training. In the unrestricted analysis, increased activity was found in the parahippocampal gyrus 1 h after the tongue-task training and remained for a week. Decreased activity was found in right post-central and middle frontal gyri 1 h and 1 week post-training. The results verified the involvement of specific corticomotor areas in response to tongue protrusion. Short-term tongue-task training was associated with longer-lasting (up to 1 week) changes in motor-related brain activity. The results suggested that primary motor areas are involved in the early and late stages, while other motor areas mainly are engaged in the later stage of corticomotor neuroplasticity of the tongue.

Tooth Movement Efficacy of Retraction Spring Made of a New Low Elastic Modulus Material, Gum Metal, Evaluated by the Finite Element Method.

The aim of this study was to evaluate the tooth movement efficacy of retraction springs made of a new ß-titanium alloy, "gum metal", which has a low Young's modulus and nonlinear super elasticity. Using double loop springs incorporated into an archwire made of gum metal (GUM) and titanium molybdenum alloy (TMA), the maxillary anterior teeth were moved distally to close an extraction space. The long-term movements were simulated by the finite element method. Its procedure was constructed of two steps, with the first step being the calculation of the initial tooth movement produced by elastic deformation of the periodontal ligament, and in the second step, the alveolar socket was moved by the initial tooth movement. By repeating these steps, the tooth moved by accumulating the initial tooth movement. The number of repeating calculations was equivalent to an elapsed time. In the GUM and TMA springs, the anterior teeth firstly tipped lingually, and then became upright. As a result of these movements, the canine could move bodily. The amount of space closure in GUM spring was 1.5 times that in TMA spring. The initial tipping angle of the canine in the GUM spring was larger than that in the TMA spring. The number of repeating calculations required for the bodily movement in the GUM spring was about two times that in the TMA spring. It was predicted that the speed of space closure in the GUM spring was smaller than that in the TMA spring.

Assessment of Hounsfield unit in the differential diagnosis of odontogenic cysts.

OBJECTIVES: The purpose of this study was to evaluate the usefulness of Hounsfield unit (HU) assessment with multislice-CT in the differentiation of radicular cysts (RCs), dentigerous cysts (DCs) and odontogenic keratocysts (OKCs). METHODS: In total, 307 odontogenic cysts (RCs, DCs and OKCs) were included in this study. Cysts with lesion diameter <10 mm, cysts with artefacts affecting measurement of HU values, cysts involving infection and recurrent cysts were regarded as exclusion criteria. Images were acquired in three different types of CT scanners: Aquilion ONE, Discovery CT750 HD and SOMATOM Definition Flash. Differences in HU values among scanners and among types of odontogenic cysts were assessed using one-way analysis of variance; multiple comparisons were performed post hoc, using the Tukey-Kramer honestly significant difference test. RESULTS: In total, 164 cysts were analysed in this study (64 RCs, 57 DCs and 43 OKCs). Regardless of the type of lesion, the Aquilion ONE scanner demonstrated a significant difference in HU value, compared with the Discovery CT750 HD scanner. Regardless of CT scanner model, HU values significantly differed between DCs and OKCs (p < 0.0001), as well as between OKCs and RCs (p < 0.0001). CONCLUSIONS: HU values were found to vary among CT scanners and should always be associated with other lesion imaging features while interpreting and elaboration diagnostic hypothesis. Notably, the results suggested that OKCs might be able to be differentiated from DCs and RCs by using HU values.

Dynamic contrast-enhanced MRI as a predictor of programmed death ligand-1 expression in patients with oral squamous cell carcinoma.

Immune checkpoint inhibitors (ICIs) targeting programmed death ligand-1 (PD-L1) are highly promising therapies for oral squamous cell carcinoma (OSCC). The assessment of PD-L1 expression may help predicting the therapeutic effect of ICIs and, thus, benefit patient selection. Contrast index (CI) parameters derived from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) have been proven as efficient to assess microvessel density (MVD) in OSCC. The present study aimed to determine the correlation between DCE-MRI parameters and MVD and between DCE-MRI parameters and PD-L1 expression to determine whether DCE-MRI could be used non-invasively to evaluate PD-L1 expression in patients with OSCC. A total of 21 patients with primary OSCC who had undergone a 3T MRI scan, including DCE-MRI, were included in the present study, and CI curve-derived parameters were examined. The MVD and PD-L1 expression in the surgically resected specimens were analyzed using immunohistochemistry (IHC) staining for CD31 and IHC staining for PD-L1, respectively. The results demonstrated that the expression levels of these markers were correlated with DCE-MRI parameters. PD-L1 expression levels were found to be significantly correlated with the maximum CI (CI-max; P=0.007), peak CI (CI-peak; P=0.007), maximum CI gain (CI-gain; P=0.006) and MVD (P=0.001) values. The mean CI-max, CI-peak, CI-gain and MVD values were significantly higher in tumors with high PD-L1 expression (P<0.05). MVD levels were also significantly correlated with the time of CI-max (T-max; P=0.003) and CI-gain (P=0.037). The mean CI-gain was significantly increased, and the mean T-max was significantly shorter in high MVD tumors (P<0.05 and P<0.01, respectively). In summary, the findings from the present study confirmed the correlation between CI parameters, derived from DCE-MRI, and MVD, and suggested that these parameters may be correlated with PD-L1 expression in OSCC tumor cells.

Application of diffusion-weighted magnetic resonance imaging in the diagnosis of odontogenic lesions: a systematic review.

OBJECTIVES: This systematic literature review addresses the use of diffusion-weighted magnetic resonance imaging (DWI) and apparent diffusion coefficient (ADC) for the evaluation of benign maxillomandibular odontogenic lesions. STUDY DESIGN: Databases were searched, and original research studies or case report manuscripts up to April 2019 were included, using the keyword "diffusion," combined with the keywords "maxillofacial pathology," "oral pathology," "odontogenic tumors," "dental tissue neoplasms," "odontogenic cysts," and the histologic denomination of benign odontogenic lesions, according to the World Health Organization classification. Only English language articles and studies pertaining to DWI were selected. RESULTS: Fifteen investigations (11 original articles and 4 case reports) of distinct benign odontogenic lesions were included. Most studies did not include exclusively odontogenic lesions in their samples. CONCLUSIONS: It is too early to reach a conclusion that DWI and ADC can provide useful information in the differentiation of the histologic type of some benign odontogenic lesions on the basis of available data in the literature.

Incidental findings in the thyroid gland on computed tomography images of the oral and maxillofacial region.

The numbers of abnormal findings incidentally detected in adjacent regions are increasing with advances in imaging modalities. The present study aimed to examine the prevalence and characteristics of incidental findings in the thyroid gland on computed tomography (CT) images of the oral and maxillofacial region. CT scans of the oral and maxillofacial region in patients obtained between January 2012 and December 2016 were retrospectively reviewed. Images that revealed incidental findings in the thyroid gland, including nodules, were recorded, together with the sizes and characteristics of the findings. The Japan Association of Breast and Thyroid Sonology (JABTS) guidelines were used for classification. The rate of descriptions of these findings in the radiographic interpretation reports were also examined. Of the 1,135 patients examined, 326 (28.7%) had several types of incidental findings. In particular, 169 (14.9%) of the 1,135 patients had nodules >5 mm in diameter, for which further careful examination is recommended in the JABTS guideline. The description rate for nodules >5 mm in diameter in the radiographic interpretation reports was 30.8% (52/169 patients), of whom 17.3% (9/52 patients) were referred to the endocrinology department for further careful examination. Incidental findings in the thyroid gland were relatively common on CT images of the oral and maxillofacial region. Oral radiologists tend to focus specifically on the oral and maxillofacial region during diagnosis on oral and maxillofacial CT images, but should pay the same careful attention to observe adjacent regions, such as the thyroid gland.

Fourth molar: A retrospective study and literature review of a rare clinical entity.

PURPOSE: The prevalence of supernumerary teeth has been reported to be between 0.1% and 3.8%. The aim of this study was to determine the prevalence, clinical significance, and associated pathologies of fourth molars based on a retrospective study and a literature review. MATERIALS AND METHODS: A 5-year retrospective prevalence study was conducted at the Department of Oral Diagnosis and Dentomaxillofacial Radiology of Okayama University Hospital, Okayama, Japan. The study involved extracting data from the digital records of patients from January 1, 2013 through December 31, 2017. The sampling frame included all patients who had panoramic radiographs, cone-beam computed tomography (CT), and multislice CT images during the period under review. RESULTS: A total of 26,721 cases were reviewed and 87 fourth molars were identified. The prevalence of fourth molars in the 5-year study at Okayama was calculated as 0.32%. The mean age of patients with a fourth molar was 30.43 years, and the male-to-female ratio was 1:0.98. The vast majority of cases were in the maxilla (92%) and had normal shapes (89.7%); furthermore, 82.8% of cases were unerupted. CONCLUSION: The prevalence of fourth molars in the study population was found to be 0.32%, and fourth molars occurred with approximately equal frequency in males and females. Fourth molars were more common in the maxilla and were predominantly unerupted and small.

Application of diffusion-weighted magnetic resonance imaging in the diagnosis of salivary gland diseases: a systematic review.

OBJECTIVES: The aim of this systematic literature review was to focus on the use of diffusion-weighted magnetic resonance imaging (DWI) in the evaluation of salivary gland diseases. STUDY DESIGN: Databases were searched, and original research manuscripts up to 2018 were identified by using the keywords "diffusion" combined with "salivary gland," "salivary gland neoplasm," "sialadenitis," "parotid gland," "submandibular gland," "sublingual gland," "minor salivary gland," "salivary gland fistula," "salivary gland calculi," "salivary ducts," "xerostomia," and "sialorrhea." Only English language manuscripts and studies pertaining to DWI were selected. RESULTS: In all, 66 investigations regarding various salivary gland diseases, such as neoplasms, postirradiation changes, and inflammatory and autoimmune diseases, were included. Most study objectives involved the use of the apparent diffusion coefficient (ADC) in differentiating between benign lesions and malignant neoplasms. Histologic features of evaluated samples were heterogeneous. CONCLUSIONS: DWI may improve the differential diagnosis of salivary gland diseases, particularly in distinguishing between benign and malignant neoplasms. A unique ADC cutoff value could not be established because of the heterogeneity of the methods applied for ADC assessment and the heterogeneity of the diseases. DWI and the ADC are valuable tools in the diagnosis of salivary gland disease.

Oropharyngeal adenoid cystic carcinoma invading the mandibular bone through the mandibular foramen.

Adenoid cystic carcinoma (ACC) is a rare epithelial tumor of the head and neck region, and one of the most common malignant tumors of the salivary glands. ACC is a slow-growing tumor characterized by perineural invasion and often has a high-recurrence rate. We describe a case of oropharyngeal ACC invading the mandibular bone through the mandibular foramen that showed a rare pattern of origin and invasion. A 70-year-old woman complained of noise and pain around the right temporomandibular joint. Osteomyelitis was suspected on the initial imaging examinations, although the findings were slightly atypical. However, a mass was observed in the right oropharyngeal wall on subsequent imaging examinations, and mandibular bone invasion, rather than osteomyelitis, was additionally suspected. The mass in the right oropharyngeal wall and right mandible was surgically excised. On postoperative histopathological examination, the mass was finally diagnosed as ACC. As tumor cells were also observed around the inferior alveolar nerve, mandibular bone invasion through the mandibular foramen was suspected. An oropharyngeal ACC invading the mandibular bone through the mandibular foramen is extremely rare. The present case suggests that bone invasion should be considered carefully with several imaging examinations when a malignant tumor such as ACC is observed around the jaw bone.

A case of sublingual adenoid cystic carcinoma involving the mandible presenting as a "skip lesion".

Adenoid cystic carcinoma (ACC) is a slowly growing malignant neoplasm with a propensity for perineural invasion. Microscopic invasion of ACC often prevents its detection on computed tomography (CT) or magnetic resonance imaging (MRI). We herein report a rare case of sublingual ACC presenting as a "skip lesion" that rapidly infiltrated the mandible after tumor resection. A 64-year-old man presented to Okayama University Hospital with an 18-month history of swelling in the right floor of the mouth. Clinical examination displayed an ulcerated swollen mass in that region. An enhanced mass was detected in the right sublingual space on CT and MRI. Bone surface erosion was observed at the inferior border of the mandible, but continuity with the sublingual mass or mass around that lesion was not detected by imaging. Sublingual tumor resection and selective neck dissection were performed by the pull-through method. Histopathologically, the surgical margins were free of cancer cells, and the tumor was diagnosed as ACC. Continuity with the sublingual mass and mandibular bone was not detected intraoperatively. However, marked bone resorption was detected in the anterior mandible 3 months after the operation. Biopsy was performed, and the findings indicated the same histological type of sublingual ACC. This case suggests that a malignant tumor close to the jaw bone requires the clinician to consider the possibility of bone invasion and to observe a wide region surrounding the tumor using imaging examination.