Computed Tomographic Findings in Injured Free-Living Gopher Tortoises (Gopherus polyphemus)
Abstract
Free-living turtles and tortoises commonly present to veterinary facilities for trauma. The superimposition of shell structures and lack of diffuse adipose tissue limits plain radiographic assessment of tissue damage; computed tomography (CT) is more sensitive in detecting these lesions. The purpose of this study was to retrospectively document common CT lesions associated with trauma. This retrospective study evaluated medical records and CT findings of 131 wild gopher tortoises (Gopherus polyphemus) with trauma that presented to the Zoological Medicine Service, University of Florida, from 2015 to 2020. The most common injury was carapacial fractures, which were detected in 115 tortoises (88%), followed by coelomic involvement (n = 88, 67%), soft tissue intra-coelomic non-pulmonary lesions (n = 76, 58%), plastron fractures (n = 67, 51%), extra-coelomic soft tissue lesions (n = 61, 47%), pulmonary lesions (n = 59, 45%), appendicular fractures (n = 56, 43%), vertebral lesions (n = 38, 29%), and skull fractures (n = 8, 6%). CT is helpful for effectively evaluating and managing mild to moderate trauma in gopher tortoises because it allows the identification of significant internal injuries that can affect release to the wild if untreated. In this retrospective study, it was essential for assessing spinal traumas, as well as identifying lung collapse and pectoral and pelvic fractures.
Introduction
The most common reason for presentation of free-living chelonians to veterinary facilities is trauma, primarily due to vehicles, dog attacks, and lawn mowers (Brown and Sleeman, 2002; Fleming, 2008; Schrader et al., 2010; Rivas et al., 2014; Bercier, 2015; Sack et al., 2017). Injury to gopher tortoises (Gopherus polyphemus) in Florida, USA, is of major concern because of their declining population due to habitat loss and their role as a keystone species (McCoy et al., 2006).
Trauma assessment in chelonians has traditionally been performed with plain radiography. Computed tomography (CT), however, has previously been used for evaluation of skeletal injuries in chelonians and has been proven superior to plain radiography in the detection and diagnosis of lesions (Gumpenbergr and Henninger, 2001; Abou-Madi et al., 2004). Several other benefits of CT include differentiation of fluid and soft tissues, ability to perform reconstructions, and use of intravenous contrast to enhance soft-tissue detail. A CT is particularly helpful for complex chelonian shell fractures because it allows assessment of severity, displacement of bone, involvement of the vertebrae, and abnormalities of the vertebral canal (Kiefer and Pees, 2011). The use of CT, therefore, enhances the ability of the clinician to assess the extent of the injury, accurately evaluate internal lesions, and confirm lesions in vital skeletal structures. Ultimately, the information obtained from CT is used for diagnostic and therapeutic purposes.
Currently, a lack of information is available regarding CT lesions associated with trauma in gopher tortoises. The main objective of this study is to retrospectively document CT lesions in gopher tortoises with trauma.
Materials and Methods
Animals
The medical records of injured gopher tortoises presented to the Zoological Medicine Service, University of Florida (Gainesville, FL, USA), between January 2015 and October 2020 were reviewed. For inclusion in this study, we required they be free-living, had lesions consistent with trauma, a whole-body CT, and known final disposition (i.e., euthanasia, spontaneous death, alive nonreleasable, released). All medical records of gopher tortoises presented during the study period were reviewed, but only the ones that fit the inclusion criteria were included in the analysis. Approval by the Institutional Animal Care and Use Committee of the University of Florida was not required.
Medical records
Medical record information was collected by a single operator (AC). The collected patient information included accession number, admission date, sex, probable cause (i.e., road traffic accident, animal attack, equipment-induced, unknown), trauma type (i.e., blunt vs. bite), days in hospital, final disposition (i.e., euthanasia, spontaneous death, alive, nonreleasable, released), and date of death (if applicable). The etiology of trauma was based on the previous radiology interpretation report. If this information was missing, a board-certified veterinary radiologist (FVG) attempted to determine the etiology of trauma via CT evaluation (Fig. 1). Admitting clinicians also decided the cause of trauma based on gross findings (e.g., evidence of presumptive tooth marks). If sex was not noted in the medical records, the shape of the plastron and presence of follicles or eggs were evaluated on CT.
Citation: Journal of Herpetological Medicine and Surgery 35, 4; 10.5818/JHMS-D-24-00002
CT technique
Scans were performed using a 160-slice (Aquilion Prime) multidetector row, helical CT unit (Toshiba Medical Systems, Inc., Tustin, CA, USA) with the tortoises in ventral recumbency. Scans were performed in helical acquisition mode with a slice thickness of 0.5 mm; pitch of 0.8, 100 mA, 120 kVp; tube rotation time of 0.5 sec; and a 512 × 512 matrix. Tortoises were usually restrained in place with a radiolucent box.
Images were reconstructed into transverse, sagittal, and dorsal planes using soft tissue or bone algorithms. In some cases, tridimensional reconstructions were also available. The slice thickness of the reformatted images was variable, ranging between 0.5 and 5 mm, and the display field of view was tailored to patient size. Three tortoises received contrast solution (600 mg/kg iohexol; Omnipaque, 300 mg Iodine/mL; GE Healthcare, Inc., Cork, Ireland) via subcarapacial sinus. Images were acquired approximately 8 to 20 sec after contrast administration.
CT image review
Categorization of CT lesions included carapace, plastron, thoracic limb, pelvic limb, skull, vertebral column, coelomic cavity (presence of free fluid or gas attenuation), and soft tissue involvement (i.e., intra-coelomic nonpulmonary, pulmonary, or extra-coelomic). The CT was evaluated for primarily traumatic lesions (Table 1). The carapace was further categorized as vertebral, costal, marginal, nuchal, and supracaudal scutes (Fig. 2). The plastron was further categorized as gular, intergular, axillary, humeral, pectoral, abdominal, femoral, and anal scutes (Fig. 2). The vertebral column was further categorized as cervical, dorsal, sacral, and caudal vertebrae with or without the presence of pneumorrhachis (presence of gas in the spinal canal) or luxation. Results included in this study originated from the previous reports at the initial time of the assessment.
Citation: Journal of Herpetological Medicine and Surgery 35, 4; 10.5818/JHMS-D-24-00002
Statistical analysis
For the descriptive analysis, categorical data was collected from existing medical records and tabulated using Excel (Microsoft Corporation, Redmond, WA, USA). A Kolmogorov-Smirnov test was performed to evaluate normality in body weight distribution and urolith size distribution.
Results
Animals
Between January 1, 2015, and October 7, 2020, 316 free-living gopher tortoises were evaluated by the zoological medicine service. A total of 131 (41%; 77 female, 54 male) met the inclusion criteria for this study. Weights were found to be normally distributed using a Kolmogorov-Smirnov test and ranged from 0.13 kg to 7.21 kg with a mean ± 1 SD of 2.59 ± 1.39 kg. The majority (66%) of tortoises presented between May to October. A total of 86 (66%) and 45 (34%) presented for blunt and animal-bite trauma, respectively. Eighty-five (65%) gopher tortoises were nonreleasable (i.e., euthanasia [n = 57], spontaneous death [n = 11], or alive nonreleasable [n = 17]), whereas 46 (35%) were released. On average, released gopher tortoises were hospitalized for 68 days (2 to 321 days). Euthanized gopher tortoises were hospitalized for an average of 18 days (1 to 273 days). Nonreleasable gopher tortoises were hospitalized an average of 125 days (8 to 438 days). Tortoises that spontaneously died were hospitalized on average 23 days (2 to 98 days).
CT lesions
Specific lesion location is summarized in Table 2. The most common injury was carapacial fractures, which were detected in 115 tortoises (88%), followed by coelomic involvement (n = 88, 67%), soft tissue intra-coelomic nonpulmonary lesions (n = 76, 58%), plastron fractures (n = 67, 51%), extra-coelomic soft tissue lesions (n = 61, 47%), pulmonary lesions (n = 59, 45%), appendicular fractures (n = 56, 43%), vertebral lesions (n = 38, 29%), and skull fractures (n = 8, 6%; Figs. 3–7). Among all gopher tortoises with appendicular fractures, pelvic limb lesions (n = 30, 54%) were slightly more frequent than thoracic limb lesions (n = 27, 48%). Out of 38 tortoises with vertebral lesions, pneumorrhachis (n = 17, 45%) and spinal luxation (n = 9, 24%) were noted. Of 88 tortoises with coelomic involvement, pneumocoelom (n = 67, 76%) and coelomic effusion (n = 37, 42%) were commonly identified lesions. Of 76 tortoises with soft tissue intra-coelomic nonpulmonary lesions, most were considered incidental, nontraumatic (n = 71, 93%) including uroliths (n = 65, 86%), cholecystolithiasis (n = 4, 3%), renal mineralization (n = 2, 1.5%), and mineralized gastrointestinal contents (n = 22, 16.8%). Urolith was the most predominant nontraumatic soft tissue intra-coelomic nonpulmonary lesion (n = 65, 86%).
Citation: Journal of Herpetological Medicine and Surgery 35, 4; 10.5818/JHMS-D-24-00002
Citation: Journal of Herpetological Medicine and Surgery 35, 4; 10.5818/JHMS-D-24-00002
Citation: Journal of Herpetological Medicine and Surgery 35, 4; 10.5818/JHMS-D-24-00002
Citation: Journal of Herpetological Medicine and Surgery 35, 4; 10.5818/JHMS-D-24-00002
Citation: Journal of Herpetological Medicine and Surgery 35, 4; 10.5818/JHMS-D-24-00002
Urolith sizes were found not to be normally distributed by a Kolmogorov-Smirnov test and had a mean diameter of 4.7 mm, a median diameter of 4 mm, a range of 1.4 mm–20 mm, and an interquartile range of 2.4 mm–6 mm. Of 61 tortoises with extra-coelomic soft tissue lesions, the most common lesion was subcutaneous emphysema (n = 37, 61%).
Only three tortoises (2%) were administered contrast, improving the visualization of the intra-coelomic organs and coelomic effusion in two of them. In the third case, inadequate absorption of the contrast and organ contrast enhancement was noted. No additional lesions were detected on postcontrast images as compared with precontrast images in these animals.
Discussion
This study retrospectively documented CT lesions in gopher tortoises associated with trauma. Our findings indicate that CT is helpful for evaluating traumatic lesions in gopher tortoises.
Not surprisingly, carapace and plastron fractures were common among traumatized gopher tortoises. Shell fractures have been reported previously as a common traumatic lesion in chelonians (Bennet and Mehler, 2006). Shell trauma ranges from simple abrasions to complex fractures with organ exposure (Sack et al., 2017). These injuries are due to the anatomical location of the shell and its function protecting vital organs. As demonstrated in this study, complex carapace fractures often involve vertebral damage due to the relationship of the shell to the spine (Hedley and Kubiak, 2015). Appendicular lesions were also frequent. Previous literature evaluating skeletal injuries in chelonians showed many appendicular fractures can be missed using plain film radiography (Abou-Madi et al., 2004). Therefore, CT is likely a better diagnostic tool.
Soft tissue intra-coelomic nonpulmonary lesions were identified in many tortoises. The majority, however, were incidental, nontraumatic, and likely did not affect outcome. The main type was uroliths. In periods of dehydration, such as associated with trauma, urates may build up and form uroliths. In a previous study evaluating uroliths in client-owned chelonians, a single, large urolith was visualized in most chelonians that received imaging. Most chelonians evaluated, however, were Mojave desert tortoises (Gopherus agassizii), a congeneric species from a significantly more xeric environment (Keller et al., 2015). Although urolith sizes were not given in that study, all of the uroliths in an earlier, smaller study of desert tortoises found uroliths of at least 30 mm in diameter, which was larger than the stones in any of our tortoises (Homer et al., 1983). Multiple, small uroliths were more common in the present study, of a size less likely to be clinically relevant.
The location of the lungs immediately ventral to the carapace means penetrating fractures often are associated with pulmonary trauma. If left untreated, the lungs do not reinflate, leading to permanent atelectasis, as well as bacterial and fungal pneumonias (McArther et al., 2004).
The use of contrast may be beneficial for identification of intracoelomic lesions, such as coelomic effusion, and improves visualization of coelomic organs. However, in this study, it was used only in three cases via injection in the subcarapacial sinus, effective only in two cases. The subcarapacial sinus, however, is not without risk. A previous report described accidental intrathecal injection in gopher tortoises following subcarapacial sinus venipuncture (Quesada et al., 2010). An additional report discusses extravasation of contrast media following subcarapacial venipuncture (Rockwell et al., 2022). Therefore, use of other routes such as the brachial and jugular veins may be safer.
Limitations are found with this retrospective study. The slice thickness of the CT scans was not standardized. Additionally, the decision to use a CT scan for evaluation of injured gopher tortoises was based on clinician, physical examination findings, and budget. Therefore, not all gopher tortoises with trauma received a CT scan. Additional limitations include limited gopher tortoises receiving contrast and lack of other clinical evaluations.
In conclusion, CT is helpful for effectively evaluating and managing mild to moderate trauma in gopher tortoises because it allows the identification of significant internal injuries that can affect release to the wild if untreated. In this retrospective study, it was essential for assessing spinal traumas, as well as identifying lung collapse and pectoral and pelvic fractures.
Disclaimer
The authors have no conflicts to disclose.
Computed tomographic tridimensional reconstructions (A, C, E) and computed tomography transverse images in a bone window (B, D, F) of a gopher tortoise (Gopherus polyphemus) with blunt trauma due to suspected auto collision (A, B) and a gopher tortoise with penetrating trauma due to dog bites (C-F). (A, B) A well-defined, sharply margined fracture extending from the lateral margin of the left marginal scutes, at a level of the pelvic limbs, and extending rightward across midline through the left costal, vertebral, and right costal scutes. (C–E) Multifocal, well-defined, sharply margined, depression fractures with variable degree of comminution along the carapace and plastron affecting multiple scutes. Bandage material is seen surrounding the tortoises on the transverse images.
Computed tomographic tridimensional reconstruction of a gopher tortoise (Gopherus polyphemus) carapace (A) and plastron (B). (A) Scute pattern is characterized as vertebral (V), costal (C), marginal (M), nuchal (N), and supracaudal (S) scutes. (B) Scute pattern is characterized as gular (G), humeral (H), pectoral (P), abdominal (Ab), femoral (F), anal (An), and intergular (not pictured) scutes.
Computed tomographic transverse image in a (A) soft tissue window (postcontrast), (C) (without contrast), (B, D, F) computed tomography transverse images in a bone window and dorsal reformat in a bone window (E) of several gopher tortoises (Gopherus polyphemus). (A) A moderate amount of coelomic effusion (asterisk) is seen. Contrast medium can be seen in the cranial coelomic vessels. (B) A moderate amount of pneumocoelom is seen mostly within the dorsal aspect of the coelomic cavity (star). Right-sided carapacial and plastral fractures are also seen (arrows). (C, D) A large amount of intravascular gas is seen within the hepatic parenchyma (arrowhead), and a small amount of gas is seen throughout the coelomic cavity. (C) A presumed large soft tissue hyperattenuating pericardiac hematoma is also noted (broad arrow). In addition, multiple carapacial and plastral fractures are also seen (arrows). (E, F) A moderate amount of intravascular gas is noted within the right kidney (arrowhead). Carapacial vertebral scute fractures are also seen (arrows), as well as pneumorrhachis (broad arrow). Bandage material is seen surrounding the tortoises (B, D).
Computed tomographic transverse image in a bone window (A) and computed tomography tridimensional reconstruction (B) of a gopher tortoise (Gopherus polyphemus) with bilateral thoracic limb wounds (arrows). Computed tomographic postcontrast sagittal reformat (C) and transverse image (D) in a soft tissue window of a gopher tortoise with a large neck laceration (arrow heads). A mild amount of coelomic effusion also occurs (asterisks).
Computed tomographic maximum intensity projection reconstructions in a bone window of two gopher tortoises (Gopherus polyphemus). (A) Bilateral scapular fractures are noted (arrows), with the left fracture being comminuted; multiple left-sided carapacial fractures are also seen (arrow heads). (B) Bilateral iliac wing fractures are visible (arrows). Bandage material is seen surrounding the tortoises.
Computed tomographic sagittal reformats in a bone window (A, C, E) and computed tomography transverse images in a bone window (B, D, F) of three gopher tortoises (Gopherus polyphemus) with vertebral trauma. (A, B) Dorsal vertebral luxation with mild ventral displacement of the vertebral column (broad arrow); (C, D) dorsal minimally displaced vertebral fracture is appreciated (broad arrow). (E, F) A comminuted and ventrally displaced dorsal vertebral fracture is seen (broad arrow). Note the presence of pneumorrhachis in all cases (arrows). Bandage material is seen surrounding the tortoises (A, B, E, F).
Computed tomographic transverse images in a bone window of the four gopher tortoises (Gopherus polyphemus) with dorsal spinal fractures that were ultimately released. (A, C, D) Minimal displacement of these fractures (arrows). (B) Left-sided transverse process fracture that did not involve the spinal canal is visible (arrowhead). (C) Presence of pneumorrhachis is noted. (A, B) Bandage material is seen surrounding the tortoises.
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