Abstract

Virtopsy has emerged as an effective and non-invasive imaging technique to augment conventional necropsy procedures for better insight into pathological and biological profile investigation in stranded cetaceans.¹ Postmortem change and decomposition begin to occur immediately upon death and are always present at necropsy and on postmortem computed tomography (PMCT). Comprehensive knowledge of the PMCT features of postmortem change and the stages of decomposition is important when interpreting PMCT because these processes may be mistaken for pathologic processes or injury.

Anatomical cross-sectional imaging reference guides on stranded common and striped dolphins head and thorax CT and MRI were,^2,3 however, only descriptions of bi-dimensional anatomy listed among corresponding anatomical cross-sections, CT and MRI scans. In veterinary medicine, there are only a few reports documenting chronological radiographic postmortem changes in the abdomen and thorax of dogs.^4,5 To the best of our knowledge, the formal literature is devoid of any reference to such PMCT features in deceased cetaceans. The study aimed to review the PMCT features of postmortem change and decomposition in deceased cetaceans with necropsy correlation.

Between March 2014 and October 2016, a total of 160 cetacean deaths were confirmed in the Hong Kong waters, Bohai waters and Yangtze river. Whole body virtopsies of 104 carcasses were performed and analyzed for pathologic findings. Five cetacean species (45 males, 53 females, 6 unknown sex; calf to adult; 50–272.5 cm in length) were included, with the carcass code ranging from 2–4. PMCT was performed using a 16-slice multi-detector row Toshiba Alexion^TM CT system or Somatom Definition 64 slices Dual Energy CT system. Post processing of virtopsy images was performed with the built-in software and/or TeraRecon Aquarius workstation (San Mateo, California). Computed tomographic findings were compared with subsequent necropsy findings.

Livor mortis increased the attenuation of vasculature and dependent tissues on PMCT. It may also produce a hematocrit effect with fluid levels evident in the great vessels and cardiac chambers from dependent layering of erythrocytes^6,7 in most beached freshly deceased carcasses or euthanized beached cetaceans. In contrast, decomposition through autolysis, putrefaction, and animal predation posed significant alterations on whole body PMCT features. Autolysis alters the attenuation of the brain quickly after death, with effacement of cerebral sulci and ventricles and loss of gray-white matter differentiation. Putrefaction induced a pattern of gas in carcasses that began intravascularly and proceeded to gaseous distension of all anatomic spaces, organs, and soft tissues. Pleural and peritoneal spaces may contain small volume of transudate, which could account for the presence of putrefactive fluid or liquefied fat. PMCT attenuation of the solid visceral organs such as liver, spleen and kidneys may not change until advanced stages of decomposition when the organs begin to fragment, degenerate, and liquefy. To conclude, knowledge of the spectrum of postmortem change and decomposition in PMCT is essential for virtopsy interpretation, which can then lead to successful pathological and biological profile investigation of deceased cetaceans.

Acknowledgements

This project was financially supported by the Hong Kong Research Grants Council [Grant number: UGC/FDS17/M07/14]. The authors would like to thank the Agriculture, Fisheries and Conservation Department of the Hong Kong SAR Government for the continuous support in this project. Sincere appreciation is also extended to veterinarians, staff and volunteers from Ocean Park Hong Kong, Ocean Park Conservation Foundation Hong Kong, and Tung Wah College for paying great effort on the stranding response and necropsy in this project. Special gratitude is owed to technicians and radiographers from Hong Kong Veterinary Imaging Center and Department of Radiology in Zhongnan Hospital Wuhan University for operating the CT units for this research.

* Presenting author

Literature Cited

1.  Kot BCW, Fernando N, Gendron S, Heng HG, Martelli P. 2016. The virtopsy approach: Bridging necroscopic and radiological data for death investigation of stranded cetaceans in the Hong Kong waters. Proceeding of 47th International Association for Aquatic Animal Medicine. Virginia Beach, VA, USA.

2.  Alonso-Farré JM, Gonzalo-Orden M, Barreiro-Vázquez JD, Ajenjo JM, Barreiro-Lois A, Llarena-Reino M, Degollada E. 2014. Cross-sectional anatomy, computed tomography and magnetic resonance imaging of the thoracic region of common dolphin (Delphinus delphis) and striped dolphin (Stenella coeruleoalba). Anat Histol Embryol. 43:221–229.

3.  Alonso-Farré JM, Gonzalo-Orden M, Barreiro-Vázquez JD, Barreiro-Lois A, André M, Morell M, Llarena-Reino M, Monreal-Pawlowsky T, Degollada E. 2015. Cross-sectional anatomy, computed tomography and magnetic resonance imaging of the head of common dolphin (Delphinus delphis) and striped dolphin (Stenella coeruleoalba). Anat Histol Embryol. 44:13–21.

4.  Heng HG, Selvarajah GT, Lim HT, Ong JS, Lim J, Ooi JT. Serial postmortem abdominal radiographic findings in canine cadavers. Forensic Sci Int. 2009;192:43–47.

5.  Heng HG, Selvarajah GT, Lim HT, Ong JS, Lim J, Ooi JT. Serial postmortem thoracic radiographic findings in canine cadavers. Forensic Sci Int. 2009;188:119–124.

6.  Dirnhofer R, Jackowski C, Vock P, Potter K, Thali MJ. 2006. VIRTOPSY: minimally invasive, imaging-guided virtual autopsy. Radiographics. 26:1305–1333.

7.  Thali MJ, Yen K, Schweitzer W, Vock P, Boesch C, Ozdoba C, Schroth G, Ith M, Sonnenschein M, Doernhoefer T, Scheurer E, Plattner T, Dirnhofer R. 2003. Virtopsy, a new imaging horizon in forensic pathology: virtual autopsy by postmortem multislice computed tomography (MSCT) and magnetic resonance imaging (MRI)-a feasibility study. J Forensic Sci. 48:386–403.