Radiological Society of North America Chest CT Classification System for Reporting COVID-19 Pneumonia: Interobserver Variability and Correlation with RT-PCR

de Jaegere, Tom M.H.; Krdzalic, Jasenko; Fasen, Bram A.C.M.; Kwee, Robert M.

PURPOSE: To evaluate the Radiological Society of North America (RSNA) chest CT classification system for reporting COVID-19 pneumonia. MATERIALS AND METHODS: Chest CT scans of consecutive patients with suspected COVID-19 were retrospectively and independently evaluated by two chest radiologists and a fifth-year radiology resident using the RSNA chest CT classification system for reporting COVID-19 pneumonia. Interobserver agreement was evaluated by calculating weighted kappa (ĸ) coefficients. Proportion of patients with real-time reverse transcriptase polymerase chain reaction (RT-PCR) confirmed COVID-19 in each of the four chest CT categories ("typical", "indeterminate", "atypical", and "negative" features for COVID-19) was calculated. RESULTS: Ninety-six patients (61 males, median age 70 years [range 29-94]) were included, of whom 45 had RT-PCR confirmed COVID-19. The number of patients assigned to chest CT categories "typical", "indeterminate", "atypical", and "negative" by the three readers ranged from 18-29, 26-43, 19-31, and 5-8 respectively. □ coefficient between the chest radiologists was 0.663 (95% confidence interval [CI]: 0.565-0.761). □ coefficients between the chest radiologists and the fifth-year radiology resident were 0.570 (95% CI: 0.443-0.696) and 0.564 (95% CI: 0.451-0.678). Proportion of patients with RT-PCR confirmed COVID-19 in the chest CT categories "typical", "indeterminate", "atypical", and "negative" for the three readers ranged from 76.9%-96.6%, 51.2%-64.1%, 2.8%-5.3%, and 20-25%, respectively. CONCLUSION: The RSNA chest CT classification system for reporting COVID-19 pneumonia has moderate to substantial interobserver agreement. However, the proportion of RT-PCR confirmed COVID-19 cases in the categories "atypical appearance" and "negative for pneumonia" is non-negligible.