The Hyperdense Right Hemidiaphragm Sign: A Novel Radiological Indicator of Diffuse Fatty Liver Infiltration on Non-Enhanced CT.

Objectives The primary objective of this study is to describe and evaluate the diagnostic performance of the hyperdense right hemidiaphragm sign (HRHS) as a novel radiological indicator for diffuse fatty infiltration of the liver on non-enhanced CT (NECT) scans. This includes assessing its sensitivity, specificity, positive predictive value, and negative predictive value, and comparing these metrics with other established NECT signs. Methods This cross-sectional multicenter retrospective study included all patients over 12 years of age who underwent both abdominal MRI and NECT scans of the abdomen within a period not exceeding six months at two tertiary hospitals (The Royal Hospital and Armed Forces Hospital, Muscat, Sultanate of Oman) between January 2010 and December 2022. Two readers reviewed the NECT scan images for the following signs: HRHS, liver density of less than 10 HU compared to the spleen, absolute liver density of <40 HU, and hyperattenuated intrahepatic vessels. The drop in signal on the out-phase sequence compared to the in-phase sequence on MRI was used as the gold standard reference for diagnosing diffuse fatty infiltration of the liver. Data were analyzed using IBM SPSS Statistics for Windows, Version 26.0 (Released 2019; IBM Corp., Armonk, NY, USA) and MedCalc software (MedCalc Software Ltd., Oostende, Belgium), with sensitivity, specificity, and positive and negative predictive values calculated for each NECT sign. Results A total of 340 patients were included in this study, with a mean age of 54 years. Among these patients, 45 were diagnosed with diffuse fatty infiltration of the liver by MRI. Thirty-six patients were identified as positive for fatty liver infiltration on unenhanced CT based on the criterion of the HRHS, with a sensitivity of 91%, specificity of 99%, positive predictive value of 94%, and negative predictive value of 99%. In contrast, 45 patients were positive using the criterion of liver density less than 10 HU compared to the spleen, yielding a sensitivity of 83%, a specificity of 98%, a positive predictive value of 88%, and a negative predictive value of 97%. Using the criterion of absolute liver density <40 HU, 30 patients were positive, with a sensitivity of 72%, specificity of 98%, positive predictive value of 90%, and negative predictive value of 96%. Lastly, 20 patients were positive using the criterion of hyperattenuated intrahepatic vessels, with a sensitivity of 51%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 93%. Conclusions The proposed qualitative evaluation using the HRHS for diffuse fatty infiltration of the liver on NECT scans demonstrates the highest sensitivity compared to other previously described NECT signs.