The contents of this page were provided by Dr. Brian Kot.
Applications of virtopsy on stranded cetaceans
Veterinary clinical and diagnostic sciences have experienced revolutionary changes in different fields, in contrast, death investigation still utilizes the century-old scalpel-based necropsy of a carcass. Although conventional X-rays have been used in the investigation of some dead cetaceans (Brook, 1994; Butti et al., 2007), multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) seem to lag behind in their postmortem application (Alonso‐Farré et al., 2014; Alonso‐Farré et al., 2015).‘Virtual autopsies’ using various radiological techniques like MDCT and MRI, named virtopsy, joining conventional dissection methods, are being introduced to the field of forensic medicine worldwide in human medicine (Dirnhofer et al., 2006; Franckenberg et al., 2015). Virtopsy has the advantages of being observer-independent, non-subjective, non-invasive, digitally storable and transferable in facilitating a second-opinion by another forensic expert or institute placed anywhere in the world. Veterinary virtual necropsy has been previously performed in lynx (Thali et al., 2007), dog (Heng et al., 2009), red kangaroo (Lee et al., 2011) and fox (Franckenberg et al., 2015). This chapter will describe the unique contribution of virtopsy to cetacean stranding investigation.
16-slice or 64 slice MDCT is used for postmortem investigation of cetaceans. The scan is operated at 100-120kV, 60-150mA, and 1mm slice thickness. Scan field of view is ranged from 183mm to 430mm. As a result of intrinsic limitation of the machine, maximum weight and height of the deceased cetaceans are limited to under 250 kg and less than 72 cm in diameter respectively. Anatomy that lies beyond the maximum gantry diameter, for instance the dorsal fin, shall be truncated prior to CT scanning. Additional mechanical support may be required for overweighed carcasses. Whole body CT scan of the deceased cetaceans can facilitate holistic summarization of pathological findings and are always suggested. In case of freshly deceased carcasses, additional examination of brain, thorax and spine can be performed using 0.25 Tesla or 3 Tesla MRI unit. Post processing of virtopsy images is performed with the built-in software and/or TeraRecon Aquarius workstation (San Mateo, California) (Tsui & Kot, 2016).
Time needed with virtopsy incorporated in stranding response procedures ranged from 6-13 hours (Figure 1) (Tsui & Kot, 2015). Although virtopsy appearance of trauma and organ diseases appears not to be differed markedly from their clinical appearances, proper diagnosis on stranded cetacean virtopsy required special training on radiology, forensic medicine and marine mammal medicine (Kot et al., 2016). Most of the radiological findings, pertaining to head and neck, heart and vascular, thorax, abdomen, vertebral column and pectoral limbs, corresponded to necroscopic findings (Kot et al., 2015). MDCT is useful in diagnosing fatal hemorrhage, organ herniation, and pathological gas collection (Figure 2), as well as determining the number, shapes and characteristics of the fractures sites and the direction of external force (Figure 3 & 4) (Kot et al., 2015; Yuen et al., 2016). MRI is effective in evaluating soft tissue lesions, musculoskeletal injuries, integrity of spinal cord and brain herniation.
Apart from pathological findings, the merit of virtopsy extends to the life history investigation of the deceased cetaceans. Assessment of cranial measurements using CT three-dimensional volume rendered images (3DVRI) may provide additional morphometrical information to identify sex, age, evolutionary history, geographical variation and sexual dimorphism (Figure 5) (Yuen et al., 2016). Radiological assessment of the degree of epiphyseal fusion/ossification at postcranial skeleton also allows individual age-at-death estimation, supplementing the data obtained by dental growth layer group pattern (Figure 6) (Wong et al., 2016). Gradual increment of postmortem gas accumulation in the brain (Figure 2), pleural cavity, mediastinum, cardiac chambers (Figure 7), esophagus, subcutaneous tissue, gastrointestinal tract (Figure 8), liver, spleen, kidney, blood vessels and musculatures could be quantified with MDCT, which might gain invaluable insight to the individual death interval.
Virtopsy is a perspective, potentially powerful tool, providing non-invasive and objective measurements to supplement the necroscopic findings for cetacean death and life history investigation. Virtopsy could also facilitate veterinary personnel to perform image-guided target specimen necropsy and sampling for histology and toxicology. The calibrated 3-D documentation and analysis of virtopsy findings would lead to qualitative improvements in conventional necropsy, since the digitally stored data might be recalled at any time to provide fresh, intact topographic and anatomic-clinical information.
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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.
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Heng HG, Selvarajah GT, Lim HT, Ong JS, Lim J, Ooi JT. 2009. Serial postmortem thoracic radiographic findings in canine cadavers. Forensic Sci Int 188: 119-124.
Kot BCW, Chu J, Fernando N, Gendron S, Heng HG, Martelli P. 2015. Can necropsy go bloodless: Applicability of virtopsy as a routine procedure in stranded cetaceans in the Hong Kong waters. Proceedings of 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, CA, USA, 13-18 December.
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.
Lee KJ, Sasaki M, Miyauchi A, Kishimoto M, Shimizu J, Iwasaki T, Miyake Y, Yamada K. 2011. Virtopsy in a red kangaroo with oral osteomyelitis. J Zoo Wildl Med 42: 128-130.
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.
Thali MJ, Kneubuehl BP, Bolliger SA, Christe A, Koenigsdorfer U, Ozdoba C, Spielvogel E, Dirnhofer R. 2007. Forensic veterinary radiology: ballistic-radiological 3D computertomographic reconstruction of an illegal lynx shooting in Switzerland. Forensic Sci Int 171: 63-66.
Tsui CL, Kot BCW. 2015. Cetacean stranding response program with virtopsy as an integral part in Hong Kong: Pitfalls in management. Proceedings of 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, CA, USA, 13-18 December.
Tsui CL, Kot BCW. 2016. Role of image reformation techniques in postmortem computed tomography imaging of stranded cetaceans. Proceeding of 47th International Association for Aquatic Animal Medicine, Virginia Beach, VA, USA.
Wong KHC, Lam CSC, Ling APH, Tsui CL, Wong BLY, Kot BCW. 2016. Utilization of computed tomography in assessing fusion pattern of vertebral non-epiphyseal suture in indo-pacific finless porpoise (Neophocaena phocaenoides) in the Hong Kong waters. Proceeding of 47th International Association for Aquatic Animal Medicine, Virginia Beach, VA, USA.
Yuen HLA, Tsui CL, Kot BCW. 2016. Preliminary assessment of cranial cervical dislocation in stranded cetaceans using multislice computed tomography. Proceeding of 47th International Association for Aquatic Animal Medicine, Virginia Beach, VA, USA.
Yuen, HLA., Tsui, CL., Kot, BCW. In press. Accuracy and reliability of cetacean cranial morphometrics using computed tomography three-dimensional volume rendered images. PloS ONE.