Unveiling the diagnostic accuracy of PMCT: Detection of pneumonia considering postmortem changes and time intervals

• This study investigated the diagnostic accuracy of PMCT for detection of pneumonia. • 212 lung lobes of 53 patient were available for analysis in this retrospective cohort. • There is a very weak positive correlation between the PTI and severity of GDA. • PMCT is not sensitive for the detection of pneumonia, but specificity is high. • PMCT performed slightly better in subgroups with a short PMI and less extensive GDA. Postmortem CT (PMCT) faces challenges in assessing lung parenchyma due to images being acquired in expiratory state, leading to varying severity of pulmonary edema redistribution with gravity-dependent attenuation ranging from ground glass to full opacification. This retrospective study assessed the effect of gravity-dependent attenuation and the postmortem time interval (PTI) on the diagnostic accuracy of PMCT for detecting acute pneumonia. Deceased patients who underwent PMCT and autopsy were included. Consensus evaluations by two radiologists and two pathologists re-examined images and histological samples of separate lung lobes. Scores were assigned for radiological and histological findings, including the presence of acute pneumonia, gravity-dependent attenuation severity, and pulmonary edema. PTI was calculated and correlated with gravity-dependent attenuation severity. Crosstabs were created to calculate diagnostic parameters. Fifty-seven patients were included, with four excluded and 44 fully opacified lung lobes. 168 lung lobes remained for analysis. The average PTI was 22 hours and 47 min. A weak correlation was observed between PTI and gravity-dependent attenuation severity (τb = 0.125, p = 0.016). Acute pneumonia prevalence was 24,4 %, with sensitivity and specificity of PMCT for all lung lobes at 31,71 % and 85,83 %, respectively. PMCT performed better in subgroups with none or slight gravity-dependent attenuation and in patients scanned within 16 hours after death. Interpretation of lung parenchyma with PMCT is challenging. Statistical power was limited due to a limited sample size. PMCT is more suited for excluding acute pneumonia than detecting its presence. Prolonging PTI should be avoided, as increasing gravity-dependent attenuation severity over time limits PMCT sensitivity.