Lateral Teardrop Sign: A New Distinguishing Feature of Anteroposterior Projection of Chest Radiograph

Introduction: The posteroanterior (PA) projection is the standard view for chest radiographs with the alternative of anteroposterior (AP) chest view. Proper identification of the projection of any chest radiograph is critical to the interpretation and eventual inferences made. The teardrop sign in radiology is a well‑known feature that is observed wherever two or more bones are projected over one another. This article aims to introduce a lateral teardrop sign seen on AP projections of the chest and to assess its prevalence and predictive value as a distinguishing parameter between AP and PA views of the chest radiograph. Methodology: This retrospective observational study was conducted at the outpatient X‑ray unit of the Department of Radiology, University College Hospital, Ibadan. Chest radiographs with AP and PA projections acquired between August 25, 2021, and July 15, 2022, were retrieved from the Picture Archival Communication System and assessed for the presence of lateral teardrop sign. Data were analyzed using the Statistical Package for the Social Sciences (SPSS) version 25. Results: Two hundred and seven radiographs were retrieved and analyzed. These included radiographs of 106 (51.2%) males and 101 (48.8%) females. Eighty‑eight (42.5%) were taken in the AP projection while 119 (57.5%) were PA. Only 46 (22.2%) of these radiographs showed the lateral teardrop sign. Of the 46 radiographs showing the sign, 45 (97.8%) were AP constituting 51.1% of all AP radiographs. One hundred and eighteen (73.3%) of radiographs without the sign were PA. A negative and positive predictive value of 73.5% and 98.9% were calculated, respectively, for the lateral teardrop sign, with a sensitivity of 67.2% and specificity of 99.2%. Conclusion: Even though there are already existing parameters used to differentiate between AP and PA views, the presence of lateral teardrop sign can be a useful addition in the identification and distinguishing of AP radiographs.