OBJECTIVES/HYPOTHESIS: Inverted papillomas (IPs) are benign tumors of the sinonasal tract with a malignant transformation potential. Predicting the transformation propensity of IPs and corresponding risk factors has long been a challenge. In this study, we aimed to use radiographic findings on magnetic resonance imaging (MRI) and computed tomography (CT) to help differentiate IP from IP-transformed squamous cell carcinomas (IP-SCC).STUDY DESIGN: Retrospective cohort study.METHODS: A retrospective analysis was performed at two institutions comparing IP (n=76) and IP-SCC (n=66) tumors, evaluating preoperative radiographic imaging with corresponding surgical pathology reports. The presence of a convoluted cerebriform pattern (CCP) using postcontrast T1-weighted and T2-weighted MRI was evaluated. Using MRI diffusion-weighted imaging (DWI), we calculated the apparent diffusion coefficient (ADC) value of each tumor. We also determined the tumor origin, attachment sites, and presence of bony erosion using CT imaging.RESULTS: Benign IPs had a higher prevalence of CCP on MRI compared to IP-transformed SCC (P=.0001. The mean value ADC of malignant IP-SCC (ADCb0,1000 =1.12*10-3 mm2 /s) was significantly lower than that of benign IPs (ADCb0,1000 =1.49*10-3 mm2 /s, P=.002). IP-SCC tumors were more likely to be have orbital wall attachment (P=.002) and bony erosion (P<.0001) compared to IPs.CONCLUSIONS: Evaluation of CCP and DWI with ADC values on MRI are promising qualitative and quantitative methods to help differentiate benign IP tumors from their transformed malignant counterparts. Malignant IP-SCCs are associated with a loss of CCP and lower ADC values. Findings of orbital wall involvement and bony erosion on CT may also help determine presence of malignancy.LEVEL OF EVIDENCE: 4 Laryngoscope, 2018.
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