Evaluation of the mediastinal-thoracic volume ratio on postmortem computed tomography

Abstract

Objectives: The aim of this study was to measure the mediastinal-thoracic volume ratio (CTR_VOL) on PMCT as a more accurate version of traditional CTR, in order to assess the terminal positional relationship between the heart and lungs in the different causes of death with regard to age, gender, BMI, cardiomegaly, and lung expansion.

Materials: Two hundred fifty consecutive postmortem cases with pre-autopsy PMCT and full forensic autopsy were retrospectively evaluated. The lungs and the mediastinum were manually segmented on the PMCT data and the correspondent volumes were estimated in situ. CTR_VOL was calculated as the ratio of the mediastinal to the thoracic volume. The volume measurements were repeated by the same rater for the evaluation of the intrarater reliability. Age, gender, body weight and height, heart weight at autopsy, and cause of death were retrieved from the autopsy reports. Presence of lung expansion was radiologically evaluated in situ.

Results: CTR_VOL was positively associated with age and BMI but not with gender and was higher for cardiomegaly compared to normal hearts, lower for asphyxiation-related deaths compared to cardiac deaths and intoxications, and lower for cases with lung expansion. The intrarater reliability was excellent for the calculated volumes of both lungs and mediastinum.

Conclusion: The results of the present study support CTR_VOL as a tool to assess the relationship between the heart and lungs in situ, which differs significantly between the studied cause of death categories.

Keywords: Cardiothoracic ratio; Cause of death; Postmortem computed tomography; Segmentation; Three-dimensional (3D); Virtopsy.

Fig. 1

Study flow chart

Fig. 2

3D Slicer environment presenting the final 3D models of two cases after segmentation of the right lung (green), the left lung (orange). and mediastinum (red). On the top: Case evaluated without lung expansion on PMCT; the lungs do not touch each other at the anterior mediastinal space. Heart weight was normal at autopsy. CTR_VOL was calculated 25.3%. On the bottom: Case evaluated as positive for lung expansion; the lungs touch each other anteriorly. Heart weight was normal at autopsy. CTR_VOL was calculated 14.7%

Fig. 3

3D Slicer environment with the PMCT data of a male with cause of death hanging, normal heart weight at autopsy, and no lung expansion on PMCT: Segmentation of the right lung (green), the left lung (yellow), the mediastinum (red) with the final 3D model. Hilus, vessels, and whole pulmonary tissue independent of internal livors or edema were included in the pulmonary volume. Paracardial fat tissue was included in the mediastinal volume measurements. CTR_VOL% was calculated 25.6% in this case

Fig. 4

Left on the top: Boxplots depicting CTR_VOL with regard to cardiomegaly. CTR_VOL was greater for cardiomegaly compared to normal hearts (Welch’s t-test: p < 0.001). Right on the top: CTR_VOL with regard to lung expansion. CTR_VOL was lower in lung expansion compared to no expansion (Welch’s t-test: p < 0.001). On the bottom: CTR_VOL with regard to cardiomegaly in the distinct lung expansion groups. CTR_VOL was greater for cardiomegaly compared to normal hearts within the distinct lung expansion groups (within both expansion and no expansion: Student’s t-test: p < 0.001). CTR_VOL was lower in lung expansion compared to no expansion within the distinct heart groups (within both cardiomegaly and normal hearts: Student’s t-test: p < 0.001)

Fig. 5

On the top: Boxplots depicting CTR_VOL in the different cause of death groups. Differences were found between cardiac deaths and all other causes of death, between intoxication and drowning, and between intoxication and hanging (pairwise post hoc: all p < 0.05). In the middle: CTR_VOL in the two cause of death categories independently of lung expansion or cardiomegaly. CTR_VOL was lower for “asphyxiation” compared to “cardiac-intoxication” (Student’s t-test: p < 0.001). Left on the bottom: CTR_VOL in the two cause of death categories with regard to lung expansion. CTR_VOL was lower for “asphyxiation” compared to “cardiac-intoxication” within the both lung expansion groups (within both expansion groups: Student’s t-test: p < 0.001). Right on the bottom: CTR_VOL in the two cause of death categories with regard to cardiomegaly. CTR_VOL was lower for “asphyxiation” compared to “cardiac-intoxication” within the distinct heart groups (within both heart groups: Student’s t-test: p < 0.001)

Fig. 6

CTR_VOL variations with regard to cause of death category (“cardiac-intoxication” or “asphyxiation”), presence of cardiomegaly, and lung expansion—same-colored cells indicate statistically significant differences of CTR_VOL between the groups, e.g., yellow-colored cells: CTR_VOL was significantly larger in the group with normal weighted hearts and no lung expansion (N = 61, 0.28 ± 0.05) compared to the group with normal weighted hearts and presence of lung expansion (N = 37, 0.21 ± 0.04). CTR_VOL was significantly larger in “cardiac-intoxication” compared to “asphyxiation,” in cardiomegaly compared to normal weighted hearts and in no lung expansion compared to presence of lung expansion, respectively. CTR_VOL was larger for cardiomegaly compared to normal hearts and larger for “cardiac-intoxication” compared to “asphyxiation” for both present and absent lung expansion. CTR_VOL was smaller for lung expansion compared to no lung expansion and larger for “cardiac-intoxication” compared to “asphyxiation” in both cardiomegaly and normal hearts. CTR_VOL was larger for cardiomegaly compared to normal hearts and smaller for lung expansion compared to no lung expansion in both “cardiac-intoxication” and “asphyxiation.”