BACKGROUND AND PURPOSE:Head and neck squamous cell carcinoma associated with human papillomavirus infection represents a distinct tumor entity. We hypothesized that diffusion phenotypes based on the histogram analysis of ADC values reflect distinct degrees of tumor heterogeneity in human papillomavirus-positive and human papillomavirus-negative head and neck squamous cell carcinomas.

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Objectives: The aim of this study was to establish diagnostic reference levels (DRLs) in the field of dental maxillofacial and ear-nose-throat (ENT) practices using cone beam CT (CBCT) in Switzerland. Methods: A questionnaire was sent to owners of CBCTs in Switzerland; to a total of 612 institutions. The answers were analyzed for each indication, provided that enough data were available. The DRLs were defined as the 75th percentile of air kerma product distribution (PKA). Results: 227 answers were collected (38% of all centers). Third quartile of PKA values were obtained for five dental indications: 662 mGy cm² for wisdom tooth, 683 mGy cm² for single tooth implant treatment, 542 mGy cm² for tooth position anomalies, 569 mGy cm² for pathological dentoalveolar modifications, and 639 mGy cm² for endodontics. The standard field of view (FOV) size of 5 cm in diameter x 5 cm in height was proposed. Conclusions: Large ranges of FOV and PKA were found for a given indication, demonstrating the importance of establishing DRLs as well as FOV recommendations in view of optimizing the present practice. For now, only DRLs for dental and maxillofacial could be defined; because of a lack of ENT data, no DRL values for ENT practices could be derived from this survey.

Although rare, masses and mass-like lesions of developmental and genetic origin may affect the paediatric craniofacial skeleton. They represent a major challenge in clinical practice because they can lead to functional impairment, facial deformation and disfigurement. The most common lesions include fibrous dysplasia, dermoid cysts, vascular malformations and plexiform neurofibromas. Less common lesions include torus mandibularis and torus palatinus, cherubism, nevoid basal cell carcinoma syndrome, meningoencephalocele and nasal sinus tract. This article provides a comprehensive approach for the evaluation of children with masses or mass-like lesions of developmental and genetic origin affecting the craniofacial skeleton. Typical findings are illustrated and the respective roles of computed tomography (CT), cone beam CT (CBCT), magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) sequences and ultrasonography (US) are discussed for the pre-therapeutic assessment, complex treatment planning and post-treatment surveillance. Key imaging findings and characteristic clinical manifestations are reviewed. Pitfalls of image interpretation are addressed and how to avoid them.Teaching points • Masses of developmental and genetic origin may severely impair the craniofacial skeleton. • Although rare, these lesions have characteristic imaging features. • CT, MRI and ultrasonography play a key role in their work-up. • Recognition of pivotal imaging pearls and diagnostic pitfalls avoids interpretation errors.

BACKGROUND AND PURPOSE: Controversy exists as to whether ADC histograms are capable to distinguish human papillomaviruspositive (HPV1) from human papillomavirus-negative (HPV-) oropharyngeal squamous cell carcinoma. We investigated how the choice of b-values influences the capability of ADC histograms to distinguish between the two tumor types.MATERIALS AND METHODS: Thirty-four consecutive patients with histologically proved primary oropharyngeal squamous cell carcinoma (11 HPV1 and 23 HPV-) underwent 3T MR imaging with a single-shot EPI DWI sequence with 6 b-values (0, 50, 100, 500, 750, 1000 s/mm 2 ). Monoexponentially calculated perfusion-sensitive (including b¼0 s/mm 2 ) and perfusion-insensitive/true diffusion ADC maps (with b $ 100 s/mm 2 as the lowest b-value) were generated using Matlab. The choice of b-values included 2 b-values (ADC b0-1000 , ADC b100-1000 , ADC b500-1000 , ADC b750-1000 ) and 3-6 b-values (ADC b0-750-1000 , ADC b0-500-750-1000 , ADC b0-50-100-1000 , ADC b0-50-100-750-1000 , ADC b0-50-100-500-750-1000 ). Readers blinded to the HPV-status contoured all tumors. ROIs were then copied onto ADC maps, and their histograms were compared.RESULTS: ADC histogram metrics in HPV1 and HPV-oropharyngeal squamous cell carcinoma changed significantly depending on the b-values. The mean ADC was lower, and skewness was higher in HPV1 than in HPV-oropharyngeal squamous cell carcinoma only for ADC b0-1000, ADC b0-750-1000 , and ADC b0-500-750-1000 (P , .05), allowing distinction between the 2 tumor types. Kurtosis was significantly higher in HPV1 versus HPV-oropharyngeal squamous cell carcinoma for all b-value combinations except 2 perfusioninsensitive maps (ADC b500-1000 and ADC b750-1000 ). Among all b-value combinations, kurtosis on ADC b0-1000 had the highest diagnostic performance to distinguish HPV1 from HPV-oropharyngeal squamous cell carcinoma (area under the curve ¼ 0.893; sensitivity ¼ 100%, specificity ¼ 82.6%). Acquiring multiple b-values for ADC calculation did not improve the distinction between HPV1 and HPV-oropharyngeal squamous cell carcinoma. CONCLUSIONS:The choice of b-values significantly affects ADC histogram metrics in oropharyngeal squamous cell carcinoma. Distinguishing HPV1 from HPV-oropharyngeal squamous cell carcinoma is best possible on the ADC b0-1000 map.ABBREVIATIONS: AJCC ¼ American Joint Committee on Cancer; AUC ¼ area under the curve; HNSCC ¼ head and neck squamous cell carcinoma; HPV1 ¼ human papillomavirus positive; HPV-¼ human papillomavirus negative; OPSCC ¼ oropharyngeal squamous cell carcinoma