Distinction between saltwater drowning and freshwater drowning by assessment of sinus fluid on post-mortem computed tomography
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To evaluate the difference in sinus fluid volume and density between saltwater and freshwater drowning and diagnose saltwater drowning in distinction from freshwater drowning.
Ninety-three drowning cases (22 saltwater and 71 freshwater) were retrospectively investigated; all had undergone post-mortem CT and forensic autopsy. Sinus fluid volume and density were calculated using a 3D-DICOM workstation, and differences were evaluated. Diagnostic performance of these indicators for saltwater drowning was evaluated using a cut-off value calculated by receiver operating characteristic (ROC) analysis.
The median sinus fluid volume was 5.68 mL in cases of saltwater drowning (range 0.08 to 37.55) and 5.46 mL in cases of freshwater drowning (0.02 to 27.68), and the average densities were 47.28 (14.26 to 75.98) HU and 32.56 (−14.38 to 77.43) HU, respectively. While sinus volume did not differ significantly (p = 0.6000), sinus density was significantly higher in saltwater than freshwater drowning cases (p = 0.0002). ROC analysis for diagnosis of saltwater drowning determined the cut-off value as 37.77 HU, with a sensitivity of 77 %, specificity of 72 %, PPV of 46 % and NPV of 91 %.
The average density of sinus fluid in cases of saltwater drowning was significantly higher than in freshwater drowning cases; there was no significant difference in the sinus fluid volume.
• Sinus fluid density of saltwater drowning is significantly higher than freshwater drowning.
• Cut-off value was 37.77 HU based on the ROC analysis.
• The cut-off value translated to 91 % NPV for diagnosis of saltwater drowning.
KeywordsDrowning Freshwater Saltwater Paranasal sinuses Computed tomography
Multi-detector computed tomography
Digital imaging and communication in medicine
Receiver operating characteristic
Positive predictive value
Negative predictive value
When a dead body is found in or around water, drowning must be considered as a cause of death. Common macroscopic findings of drowning are froth in the airway, waterlogged and over-distended lungs, pleural effusion, fluid collection in the stomach, and reduced spleen mass, among others [1, 2, 3]. However, these findings are absent in some drowning cases because the body is found long after death or has decomposed. In these cases, microscopic findings such as diatoms in the lungs, spleen, kidneys, and bone marrow serve as a basis for diagnosis of drowning [1, 2, 3]. Moreover, forensic pathologists need to specify where and why drowning occurred. Evidence of diatoms in the submerging fluid and in the victim’s body represents the current gold standard for diagnosing type of drowning . Biochemical and immunohistochemical approaches for differential diagnosis between saltwater and freshwater drowning have also been described [5, 6, 7].
In forensic medicine, post-mortem computed tomography (CT) has become common [8, 9, 10, 11]. Various CT findings of drowning have been reported, and one of the most notable findings is fluid accumulation in the maxillary or sphenoid sinuses [12, 13]. Lo Re G. et al.  also diagnosed drowning when fluids were present in the paranasal sinuses of drowned bodies. To differentiate non-drowned and drowned cadavers, an evaluation of differences in the density of the blood vessels (the resorption of freshwater in the lung results in hypodensity of the blood, representing haemodilution), and numerous other signs of drowning, including the density of the airway contents in HU, have been reported [12, 15]. Previously, we found that sinus fluid volume is significantly greater and sinus fluid density is significantly lower in drowning cases than in non-drowning cases . Although these findings can help forensic pathologists distinguish between drowning and non-drowning, they cannot provide information concerning the scene of drowning. No reported studies have suggested that differences in the density of sinus fluid content could be used to differentiate between freshwater and saltwater drowning. Therefore, in this study, we examined differences on post-mortem CT between saltwater and freshwater drowning cases.
Materials and methods
CT and autopsy
An eight-channel multi-detector row CT (MDCT) scanner (Aquilion 8; Toshiba Medical Systems, Tokyo, Japan) was used for all examinations. All subjects were scanned in a body bag while fully clothed. No contrast material was administered. In all cases, the CT scan was taken from the head to the pelvis in the helical mode (tube voltage, 120 kVp; installed mode tube current; rotation time, 0.75 sec; table speed, 14 mm per rotation; helical beam pitch, 0.875; collimations, 2.0 mm; reconstruction interval, 0).
In all cases, a forensic autopsy was performed shortly after the CT scan by a forensic pathologist with more than 30 years of experience.
All 2.0-mm slice CT image data were sent to a three-dimensional DICOM workstation (Ziostation version 188.8.131.52; Ziosoft, Tokyo, Japan). Areas of fluid in the maxillary and sphenoid sinuses on axial images were extracted manually for each slice. No multiplanar reconstruction (MPR) images were used during this process. The workstation automatically calculated the volume data and average density of the extracted fluid areas during three-dimensional volume rendering reconstruction.
Normality tests indicated that the fluid volume was not, but the fluid density was, normally distributed. Therefore, statistical significance was evaluated by the Mann–Whitney U-test and Student’s t-test, respectively. A p-value of less than 0.05 was considered to indicate a significant difference. Receiver operating characteristic (ROC) analysis was performed to determine the cut-off level, from the point on the ROC curve closest to (0, 1); i.e. the point nearest to the top left corner of the graph, and the Youden index. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for a diagnosis of saltwater drowning were calculated based on this cut-off value.
When investigating drowning cases, the scene of drowning must be determined. Histopathological, biochemical, and immunohistochemical approaches have been described [4, 5, 6, 7, 17, 18, 19, 20], but the feasibility of drowning site determination by post-mortem CT has not been investigated. Here, we demonstrate that the density of fluid accumulated in the maxillary and sphenoid sinuses was significantly higher in saltwater drowning cases than in freshwater drownings.
In our previous study, we determined that sinus fluid volume following drowning was significantly greater than in cases that had died of other causes . While the volume distribution might be presumed to depend on the composition of fluid among drowning cases, this study established that there was no significant difference in the volume between saltwater and freshwater drowning. Thus, it is not possible to presume the scene of drowning based on the fluid volume.
As the density of saltwater is higher than that of freshwater, CT attenuation values for sinus fluids following drowning would be expected to reflect this difference. Nonetheless, the validity of CT image analysis for distinguishing these fluids had not been investigated in drowning victims. This study has revealed that maxillary and sphenoid sinus fluid density as determined by post-mortem CT in saltwater drowning cases is higher than following freshwater drowning. Usumoto et al.  reported that the pleural effusion resulting from seawater drowning was characterised by a higher concentration of sodium and chloride ions compared to freshwater drowning. These differences are presumed to also be present in the paranasal sinuses and can probably partially explain the differences in fluid density. In the ROC analysis for diagnosis of saltwater drowning, the candidate cut-off value was 37.77 HU, which translated to 77 % sensitivity, 72 % specificity, 46 % PPV, and 91 % NPV. Therefore, saltwater drowning is highly unlikely when the sinus fluid density of a drowning victim is less than 37.77 HU on post-mortem CT. If a victim found in the sea or coast has sinus fluid less dense than 37.77 HU, the possibility that the victim may have drowned at another place must be considered. We also evaluated the average density of the extracted fluid areas, but did not consider differences in the density of regions within the same area. When differences were large, evaluating only the average density could constitute a methodological bias.
In our study, all diagnostic indicators of saltwater drowning were inadequate except for NPV. Christe et al.  reported that the froth in the airways, emphysema aquosum and mosaic patterns in the lung on CT were all suggestive of freshwater drowning. Ambrosetti et al.  reported that the measurement and comparison of blood-density values inside cardiac chambers may be reliable because any differences should be caused by differences in the pathophysiological mechanism underlying freshwater versus saltwater drowning; using these data could increase diagnostic performance.
Cases with pronounced decomposition were excluded from our study because saprogenous exudate would be miscible with water and affect sinus fluid density. Infant cases were also excluded because their paranasal sinuses are still unformed. As a result of the exclusion, the youngest case in this study was 19 years old; his sinuses could be assumed to be mature.
The freshwater drowning cases in this study drowned at various scenes. Differences in drowning location may be associated with differences in sinus fluid volume and density, even among freshwater drowning cases. However, we did not examine the differences in fluid volume and density among these locations because the number of drownings at each type of location was too small to be assessed statistically. This is thus a subject for future investigation.
Reproducibility of the volume and density values was not perfect because areas of fluid in the maxillary and sphenoid sinuses were extracted manually. Additionally, the volume and density values were not compared with values collected at autopsy because these data were not available for all cases.
The average density of sinus fluid in cases of saltwater drowning was significantly higher than in freshwater drowning cases, while there was no significant difference in the sinus fluid volume.
The scientific guarantor of this publication is Prof. Tadashi Ishibashi. The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article. The authors state that this work has not received any funding. No complex statistical methods were necessary for this paper. Institutional Review Board approval was obtained. Written informed consent was obtained from all subjects (patients) in this study. Methodology: Retrospective, diagnostic or prognostic study, performed at one institution.
- 1.Dolinak D, Matshes E, Lew E (eds) (2005) Forensic pathology principles and practice. Elsevier, AmsterdamGoogle Scholar
- 2.Tsokos M (ed) (2005) Forensic pathology reviews volume 3. Humana Press, New YorkGoogle Scholar
- 3.Saukko P, Knight B (eds) (2004) Knight’s forensic pathology, 3rd edn. Edward Arnold, LondonGoogle Scholar