Diagnosis of atlanto-occipital dissociation: Standardised measurements of normal craniocervical relationship in finless porpoises (genus Neophocaena) using postmortem computed tomography

Abstract

Due to the different craniocervical structures in humans and cetaceans, a standardised method assessing the normal craniocervical relationship in cetaceans is lacking, causing difficulties in defining the presence of atlanto-occipital dissociation (AOD) in cetaceans. The present study aimed to 1) describe a novel standardised method of determining the normal craniocervical relationships, and 2) define the 95% accuracy range of the normal craniocervical relationship in finless porpoises (genus Neophocaena), that allowed AOD diagnosis. Fifty-five out 83 stranded or by-caught finless porpoise carcasses were analyzed in term of their craniocervical relationship in dorsal-ventral and medial-lateral dimension, using postmortem computed tomography measurements. The normal craniocervical relationship in both dorsal-ventral (mean BD/OV: 0.87 ± 0.24 [2 SD]) and medial-lateral dimension (mean VR/VL: 0.98 ± 0.17 [2 SD]) was first defined. The 95% accuracy ranges of the normal craniocervical relationship in dorsal-ventral (0.63–1.11) and medial-lateral dimension (0.82–1.15) were proposed. The baseline ranges could facilitate AOD assessment, and provide an objective means of record for AOD related injury and death of cetaceans caused by anthropogenic trauma. The technique developed may be applied to live cetaceans with abnormal craniocervical relationship to aid diagnosis and guide corrective therapy.

Postmortem Neuroimaging of Cetacean Brains Using Computed Tomography and Magnetic Resonance Imaging

“…Virtopsy using postmortem computed tomography (PMCT) and postmortem magnetic resonance (PMMR) imaging (PMMRI) has been implemented in the pioneering virtopsydriven cetacean stranding response program in Hong Kong (HK) waters, to provide vital or additional information for conventional necropsy (Kot et al, 2016(Kot et al, , 2018(Kot et al, , 2019(Kot et al, , 2020Chan et al, 2017;Yuen et al, 2017). Stranded cetacean carcasses found in HK waters are often badly degraded (Jefferson et al, 2002) as high temperature and humidity accelerate autolysis (Klein et al, 2016), hampering stranding response personnel and veterinarians in the documentation of postmortem findings and tissue sampling (Tsui et al, 2020).…”

Virtopsy as a Revolutionary Tool for Cetacean Stranding Programs: Implementation and Management

“…Virtopsy provided numerous unique findings that could supplement and might even partially replace conventional necropsy. In this study, atlanto-occipital dissociation was commonly observed in PMCT of the stranded cetaceans Kot et al, 2018a). Skeletal anomalies, including osteolytic lesions in vertebra suggestive of spondylolysis or spondylolisthesis, physeal plate fractures or misalignment, and intramedullary bone islands, were also noted in some cases (Kot et al, 2016).…”

“…PMMRI was performed with a GE SIGNA Explorer 1.5 Tesla MR scanner (General Electric Company, Wisconsin, United States) or a 0.25 Tesla Esaote Vet MR Grande scanner (Esaote Biomedica, Genoa, Italy). Details of scanning parameters may refer to previous publications (Kot et al, 2016(Kot et al, , 2018a(Kot et al, , 2019(Kot et al, , 2020aYuen et al, 2017). Datasets were saved in DICOM 3.0 format.…”

“…Discussions regarding the modification of stranding response protocol to accommodate virtopsy, including concerns over manpower, logistics, equipment, and safety, were followed by the standardisation of virtopsy protocols. Standardised virtopsy protocols and techniques for PM pathological diagnosis were adhered to Yuen et al, 2017;Kot et al, 2018aKot et al, , 2019Kot et al, , 2020a. Pitfalls encountered were addressed with corrective measures to ensure the structural and practical management of the first Cetacean Virtopsy Stranding Response Programme (CVSRP) in the world.…”

Why to Study Opossums?

“…Like other animals of native, wild or migratory fauna, opossum are protected by the Brazilian environmental crimes law which prohibits killing, persecuting, hunting, catching or using these animals in any other way without a permit or authorization from the competent authority (Brasil, 1998). From this point of view, postmortem computed tomography (PMCT) is a valuable tool for identification and documentation of osteological structures in wild animals (Kot et al, 2018).…”