COMPUTED TOMOGRAPHIC AND CROSS-SECTIONAL ANATOMY OF THE NORMAL PACU (COLOSSOMA MACROPONUM) Author(s): Alaina Carr, D.V.M., Dipl. A.C.V.R., E. P. Scott Weber, III, V.M.D., M.Sc., Chris J. Murphy, Ph.D., Dipl. A.C.V.O. and Alison Zwingenberger, Dipl. A.C.V.R., Dipl. E.C.V.D.I. Source: Journal of Zoo and Wildlife Medicine, 45(1):184-189. 2014. Published By: American Association of Zoo Veterinarians DOI: http://dx.doi.org/10.1638/2013-0108R1.1 URL: http://www.bioone.org/doi/full/10.1638/2013-0108R1.1
BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research.
Journal of Zoo and Wildlife Medicine 45(1): 184–189, 2014 Copyright 2014 by American Association of Zoo Veterinarians
COMPUTED TOMOGRAPHIC AND CROSS-SECTIONAL ANATOMY OF THE NORMAL PACU (COLOSSOMA MACROPONUM) Alaina Carr, D.V.M., Dipl. A.C.V.R., E. P. Scott Weber III, V.M.D., M.Sc., Chris J. Murphy, Ph.D., Dipl. A.C.V.O., and Alison Zwingenberger, Dipl. A.C.V.R., Dipl. E.C.V.D.I.
Abstract: The purpose of this study was to compare and define the normal cross-sectional gross and computed tomographic (CT) anatomy for a species of boney fish to better gain insight into the use of advanced diagnostic imaging for future clinical cases. The pacu (Colossoma macropomum) was used because of its widespread presence in the aquarium trade, its relatively large body size, and its importance in the research and aquaculture settings. Transverse 0.6-mm CT images of three cadaver fish were obtained and compared to corresponding frozen cross sections of the fish. Relevant anatomic structures were identified and labeled at each level; the Hounsfield unit density of major organs was established. The images presented good anatomic detail and provide a reference for future research and clinical investigation. Key words: Anatomy, Colossoma, computed tomography, fish, pacu.
BRIEF COMMUNICATION A great number of fish species play an important role in veterinary medicine, commercial aquaculture, laboratory animal medicine, educational ambassadorship at public aquaria and zoos, stock replenishment and recreational fishing, and for hobbyists (koi ponds and display aquaria). Fish owners (commercial, public, and private) are increasingly relying on veterinary diagnostics and care to support and maintain the overall health of their aquatic animal stocks, especially as some individuals can represent a significant financial investment. Specifically, the pacu (Colossoma macropomum) is an important aquaculture species for many of the reasons stated above; its growth rate and nutritional characteristics make it useful as a food source; it is a practical lab animal for many different types of research, including toxicology; and it is often found in recreational settings and public aquariums.6,8 Intracoelomic diseases, especially those affecting the kidneys, gonads, and swim bladder, are relatively common in fish. Radiography and ultrasonography are used as first-line diagnostic imaging tools, but use of more advanced imaging techniques, such as computed From the University of California–Davis Veterinary Medical Teaching Hospital (Carr), Department of Surgical and Radiological Sciences (Murphy, Zwingenberger); the Department of Ophthalmology & Vision Sciences (Murphy); and the Department of Medicine and Epidemiology (Weber), One Garrod Drive, Davis, CA 95616, USA. Correspondence should be directed to Dr. Zwingenberger ([email protected]).
tomography (CT) and magnetic resonance imaging, is increasingly common in the research and clinical setting for morphologic studies and diagnosis of piscine disease processes.2,9 In fish, CT has been used to diagnose spinal fractures, to assess swim bladder pathology, and to aid in characterization of renal, hepatic, and coelomic neoplasia.1,3–5,7,12 There are many references available regarding CT anatomy and imaging protocols for fish; however, to the authors’ knowledge, information related to the pacu specifically is less widely available.10 The objective of this study was to clearly define the cross-sectional gross and CT appearance of the coelomic organs in the pacu for clinical use and to provide a reference for research studies. Three pacu were obtained for a separate research study that required CT of the skull and eyes. The fish were transported to the CT facility in large water-filled tubs and then euthanatized immediately prior to CT using an overdose of the anesthetic tricaine methanesulfonate (300 ppm) in a 1 : 1 ratio with water buffered with sodium bicarbonate (Tricaine-S, Western Chemical, Ferndale, Washington 98248, USA). Each fish was placed on the CT table in ventral recumbency; a short radiolucent plastic trough was used to keep the patient upright and straight. A 16-slice helical CT was used (GE Lightspeed 16, General Electric Co., Milwaukee, Wisconsin 53217, USA). The initial images were obtained at 120 kVp and 80 mAs, with a 2.5-mm slice thickness in a bone algorithm. Subsequently, iopamidol positive contrast (Isovue 200, Bracco Diagnostics, Princeton, New Jersey 08543, USA) was administered per os and per vent using a 12-
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CARR ET AL.—COMPARISON OF CT AND GROSS FISH ANATOMY
Figure 1. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 1, brain; 2, sclera; 3, vitreous; 4, lens; 5, intrachoroidal fat; and 6, operculum.
185
Figure 3. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 10, epaxial musculature; 11, vertebral spinous process; 12, vertebral neural arch; 13, spinal cord; 15, vertebral hemal arch; 16, descending aorta; 17, posterior cardinal vein; 18, anterior kidney; 19, pharynx; 20, sinus venosus; 21, hepatic vein; and 22, liver.
French feeding tube (Tyco Healthcare Group LP, Mansfield, Massachusetts 02048, USA) in order to fill the gastrointestinal tract with contrast. Between 4 and 10 ml of contrast was administered for each patient. The acquisition was repeated immediately following contrast administration. Images were reformatted into 0.6-mm slice thickness. A complete dissection of the coelomic cavity was performed in one of the fish within 24 hr of the imaging (the patient was kept in a freezer at 208C in the interim). A second fish was frozen at 208C for approximately 2 wk and was then cut into transverse sections of approximately 1-inch in thickness. The cut sec-
tions were then photographed for correlation of gross anatomic findings with CT images. On review of the CT images, the window-level was set for bone and soft tissue as needed for evaluation. Images for publication were selected based on their correlation to the gross anatomic images and overall clarity. For evaluation of the density of each organ, three different locations were selected within each organ (cranial, mid, and
Figure 2. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 6, operculum; 7, primary lamellae of the gills; 8, bulbus arteriosus; 9, pectoral girdle musculature; 10, epaxial musculature; 11, vertebral spinous process; 12, vertebral neural arch; 13, spinal cord; and 14, vertebral body.
Figure 4. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 10, epaxial musculature; 11, vertebral spinous process; 14, vertebral body; 16, descending aorta; 17, posterior cardinal vein; 22, liver; 23, dorsal fin musculature; 24, swim bladder; 25, esophagus; and 26, gall bladder.
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Figure 5. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 22, liver; 24, swim bladder; 25, esophagus; 26, gall bladder; 27, ductus pneumaticus; 28, stomach; 29, intestine; and 30, pyloric cecae.
Figure 6. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 16, descending aorta; 17, posterior cardinal vein; 22, liver; 24, swim bladder; 26, gall bladder; 28, stomach; 29, intestine; 30, pyloric cecae; 31, coelomic fat; 32, rib; and 33, intercostal musculature.
Figure 7. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 22, liver; 24, swim bladder; 26, gall bladder; 27, ductus pneumaticus; 28, stomach; 29, intestine; 31, coelomic fat; 32, rib; 33, intercostal musculature; and 34, spleen.
CARR ET AL.—COMPARISON OF CT AND GROSS FISH ANATOMY
187
Figure 8. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 22, liver; 24, swim bladder; 26, gall bladder; 27, ductus pneumaticus; 28, stomach; 29, intestine; 31, coelomic fat; 34, spleen; and 35, pelvic fin musculature.
caudal), and a small region of interest was drawn to measure the Hounsfield units (HU). This was repeated for each organ and performed in each patient separately. The HU value was then averaged for each fish individually and for the group as a whole. Overall the methods employed for the pacu fish yielded excellent imaging detail. The administration of positive contrast into the gastrointestinal tract was only partially successful and did not completely fill the entire tract in all fish. Gonadal tissue was only visible on the CT images in one fish (pacu 2, which was female, based on gross dissection). This fish was used for the initial gross dissection (therefore, transverse gross segments were not available for review). The other two fish were not sexually mature, and therefore sex was not determined at the time of the study; the high standard deviation for the gonadal tissue HU measurements is attributed to the low sample size. Figures 1–11 show the gross and CT images (prior to and after contrast administration, where applicable). Figure 12 is a sagittal reformatted image of a fish with reference lines noting the location of Figures 1–11. Table 1 lists the average HU for each organ that could be measured in these three fish. CT provided good anatomic detail, and there was good correlation between the CT images and the gross specimens. The large amount of intracoelomic fat in these patients provided good contrast with the major organs and clear visualization of the major cardiovascular structures, liver, spleen, kidneys, and gastrointestinal tract. The intracoelomic organs and musculature had HU densities within the expected normal ranges
for soft tissue structures. The CT studies were fast and easy to perform; with sedation it was postulated that these images would be relatively simple to duplicate in live fish using the techniques described in previous studies.1,5,7 Of the diagnostic imaging modalities available for use in fish, CT has distinct advantages over radiography and ultrasound. Given that some fish species have only a small amount of intracoelomic fat, radiographic detail can be poor, and evaluation of the coelom on survey images may be limited to the shape and position of the swim bladder, severely limiting the types of pathology that can be detected.11 Additionally, obtaining orthogonal images in some patients is difficult, as dorsoventral positioning can be challenging as a result of
Figure 9. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 22, liver; 24, swim bladder; 26, gall bladder; 28, stomach; 31, coelomic fat; 34, spleen; and 36, gonad.
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Figure 10. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 16, descending aorta; 26, gall bladder; 29, intestine; 31, coelomic fat; and 37, posterior kidney.
Figure 11. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 38, urinary bladder; 39, anus; and 40, anal fin musculature.
Figure 12. Sagittal reformatted image of a fish with denotation of the anatomic location of Figures 1–11.
CARR ET AL.—COMPARISON OF CT AND GROSS FISH ANATOMY
Table 1. organs.
Hounsfield units (HU) of intracoelomic
Average HU
Liver Spleen Anterior kidney Posterior kidney Coelomic fat Gonads Gall bladder Epaxial musculature Heart Brain
Standard deviation
83.6 65.4 49.4 46.3 109.2 67.2 29.2 52.1 47.6 37.3
17.6 9.8 2.8 2.0 1.5 38.8 2.3 5.4 3.3 1.6
body morphology.11 Overall, CT limits anatomic superimposition and has superior soft tissue contrast compared to radiography. When compared to ultrasound, CT image acquisition is much faster than the typical ultrasonographic exam and is more repeatable with diminished operator variability. Ultrasound is often limited to coelomic organs, affording incomplete evaluation of the skeletal and cardiovascular organs.11 This current study found that the instillation of positive contrast into the gastrointestinal tract to be a useful technique, but caution is necessary when administering the contrast in order to avoid inadvertent introduction of contrast into the coelomic cavity. It is hoped that the information presented in this article will provide a useful reference both for clinical patients and for further research studies.
LITERATURE CITED 1. Bakal, R. S., N. E. Love, G. A. Lewbart, and C. R. Berry. 1998. Imaging a spinal fracture in a Kohaku koi (Cyprinus carpio): techniques and case history report. Vet. Radiol. Ultrasound 39: 318–321.
189
2. Frank, L. 2009. Digital fish library. http://www. digitalfishlibrary.org. Accessed 26 July 2013. 3. Garland, M. R., L. P. Lawler, B. R. Whitaker, I. D. F. Walker, F. M. Corl, and E. K. Fishman. 2002. Modern CT applications in veterinary medicine. Radiographics 22: 55–62. 4. Gumpenberger, M., O. Hochwartner, and G. Loupal. 2004. Diagnostic imaging of a renal adenoma in a red oscar (Astronotus ocellatus Cuvier, 1829). Vet. Radiol. Ultrasound 45: 139–142. 5. Lewbart, G. A., G. Spodnick, N. Barlow, N. E. Love, F. Geoly, and R. S. Bakal. 1998. Surgical removal of an undifferentiated abdominal sarcoma from a koi carp (Cyprinus carpio). Vet. Rec. 143: 556–558. 6. Lopes, R. B., L. C. Paraiba, P. S. Ceccarelli, and V. Tornisielo. 2006. Bioconcentration of trichlorfon insecticide in pacu (Piaractus mesopotamicus). Chemosphere 64: 56–62. 7. Pees, M., K. Pees, and I. Kiefer. 2010. The use of computed tomography for assessment of the swim bladder in koi carp (Cyprinus carpio). Vet. Radiol. Ultrasound 51: 294–298. 8. Pullela, S. V. S. 1997. Aquaculture of Pacu (Piarctus mesopotamicus) and a Comparison of its Quality: Microbial, Sensory and Proximate Composition. Virginia Polytechnic Institute and State Univ., Blacksburg, Virginia. 9. Rowe, T. Digital morphology. http://www. digimorph.org. Accessed 26 July 2013. 10. Tyson, R., N. E. Love, G. Lewbart, and R. Bakal. 1999. Techniques in advanced imaging of fish. Proc. Am. Assoc. Zoo Vet. 1999: 201–202. 11. Weber, E. P. S., C. Weisse, T. Schwarz, C. Innis, and A. Kilde. 2009. Anesthesia, diagnostic imaging, and surgery of fish. Comp. Contin. Educ. Vet. 31: E1– E9. 12. Weisse, C., E. P. S. Weber, Z. Matzkin, and A. Kilde. 2002. Surgical removal of a seminoma from a black sea bass. J. Am. Vet. Med. Assoc. 221: 280–283. Received for publication 22 May 2013
BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research.
Journal of Zoo and Wildlife Medicine 45(1): 184–189, 2014 Copyright 2014 by American Association of Zoo Veterinarians
COMPUTED TOMOGRAPHIC AND CROSS-SECTIONAL ANATOMY OF THE NORMAL PACU (COLOSSOMA MACROPONUM) Alaina Carr, D.V.M., Dipl. A.C.V.R., E. P. Scott Weber III, V.M.D., M.Sc., Chris J. Murphy, Ph.D., Dipl. A.C.V.O., and Alison Zwingenberger, Dipl. A.C.V.R., Dipl. E.C.V.D.I.
Abstract: The purpose of this study was to compare and define the normal cross-sectional gross and computed tomographic (CT) anatomy for a species of boney fish to better gain insight into the use of advanced diagnostic imaging for future clinical cases. The pacu (Colossoma macropomum) was used because of its widespread presence in the aquarium trade, its relatively large body size, and its importance in the research and aquaculture settings. Transverse 0.6-mm CT images of three cadaver fish were obtained and compared to corresponding frozen cross sections of the fish. Relevant anatomic structures were identified and labeled at each level; the Hounsfield unit density of major organs was established. The images presented good anatomic detail and provide a reference for future research and clinical investigation. Key words: Anatomy, Colossoma, computed tomography, fish, pacu.
BRIEF COMMUNICATION A great number of fish species play an important role in veterinary medicine, commercial aquaculture, laboratory animal medicine, educational ambassadorship at public aquaria and zoos, stock replenishment and recreational fishing, and for hobbyists (koi ponds and display aquaria). Fish owners (commercial, public, and private) are increasingly relying on veterinary diagnostics and care to support and maintain the overall health of their aquatic animal stocks, especially as some individuals can represent a significant financial investment. Specifically, the pacu (Colossoma macropomum) is an important aquaculture species for many of the reasons stated above; its growth rate and nutritional characteristics make it useful as a food source; it is a practical lab animal for many different types of research, including toxicology; and it is often found in recreational settings and public aquariums.6,8 Intracoelomic diseases, especially those affecting the kidneys, gonads, and swim bladder, are relatively common in fish. Radiography and ultrasonography are used as first-line diagnostic imaging tools, but use of more advanced imaging techniques, such as computed From the University of California–Davis Veterinary Medical Teaching Hospital (Carr), Department of Surgical and Radiological Sciences (Murphy, Zwingenberger); the Department of Ophthalmology & Vision Sciences (Murphy); and the Department of Medicine and Epidemiology (Weber), One Garrod Drive, Davis, CA 95616, USA. Correspondence should be directed to Dr. Zwingenberger ([email protected]).
tomography (CT) and magnetic resonance imaging, is increasingly common in the research and clinical setting for morphologic studies and diagnosis of piscine disease processes.2,9 In fish, CT has been used to diagnose spinal fractures, to assess swim bladder pathology, and to aid in characterization of renal, hepatic, and coelomic neoplasia.1,3–5,7,12 There are many references available regarding CT anatomy and imaging protocols for fish; however, to the authors’ knowledge, information related to the pacu specifically is less widely available.10 The objective of this study was to clearly define the cross-sectional gross and CT appearance of the coelomic organs in the pacu for clinical use and to provide a reference for research studies. Three pacu were obtained for a separate research study that required CT of the skull and eyes. The fish were transported to the CT facility in large water-filled tubs and then euthanatized immediately prior to CT using an overdose of the anesthetic tricaine methanesulfonate (300 ppm) in a 1 : 1 ratio with water buffered with sodium bicarbonate (Tricaine-S, Western Chemical, Ferndale, Washington 98248, USA). Each fish was placed on the CT table in ventral recumbency; a short radiolucent plastic trough was used to keep the patient upright and straight. A 16-slice helical CT was used (GE Lightspeed 16, General Electric Co., Milwaukee, Wisconsin 53217, USA). The initial images were obtained at 120 kVp and 80 mAs, with a 2.5-mm slice thickness in a bone algorithm. Subsequently, iopamidol positive contrast (Isovue 200, Bracco Diagnostics, Princeton, New Jersey 08543, USA) was administered per os and per vent using a 12-
184
CARR ET AL.—COMPARISON OF CT AND GROSS FISH ANATOMY
Figure 1. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 1, brain; 2, sclera; 3, vitreous; 4, lens; 5, intrachoroidal fat; and 6, operculum.
185
Figure 3. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 10, epaxial musculature; 11, vertebral spinous process; 12, vertebral neural arch; 13, spinal cord; 15, vertebral hemal arch; 16, descending aorta; 17, posterior cardinal vein; 18, anterior kidney; 19, pharynx; 20, sinus venosus; 21, hepatic vein; and 22, liver.
French feeding tube (Tyco Healthcare Group LP, Mansfield, Massachusetts 02048, USA) in order to fill the gastrointestinal tract with contrast. Between 4 and 10 ml of contrast was administered for each patient. The acquisition was repeated immediately following contrast administration. Images were reformatted into 0.6-mm slice thickness. A complete dissection of the coelomic cavity was performed in one of the fish within 24 hr of the imaging (the patient was kept in a freezer at 208C in the interim). A second fish was frozen at 208C for approximately 2 wk and was then cut into transverse sections of approximately 1-inch in thickness. The cut sec-
tions were then photographed for correlation of gross anatomic findings with CT images. On review of the CT images, the window-level was set for bone and soft tissue as needed for evaluation. Images for publication were selected based on their correlation to the gross anatomic images and overall clarity. For evaluation of the density of each organ, three different locations were selected within each organ (cranial, mid, and
Figure 2. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 6, operculum; 7, primary lamellae of the gills; 8, bulbus arteriosus; 9, pectoral girdle musculature; 10, epaxial musculature; 11, vertebral spinous process; 12, vertebral neural arch; 13, spinal cord; and 14, vertebral body.
Figure 4. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 10, epaxial musculature; 11, vertebral spinous process; 14, vertebral body; 16, descending aorta; 17, posterior cardinal vein; 22, liver; 23, dorsal fin musculature; 24, swim bladder; 25, esophagus; and 26, gall bladder.
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Figure 5. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 22, liver; 24, swim bladder; 25, esophagus; 26, gall bladder; 27, ductus pneumaticus; 28, stomach; 29, intestine; and 30, pyloric cecae.
Figure 6. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 16, descending aorta; 17, posterior cardinal vein; 22, liver; 24, swim bladder; 26, gall bladder; 28, stomach; 29, intestine; 30, pyloric cecae; 31, coelomic fat; 32, rib; and 33, intercostal musculature.
Figure 7. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 22, liver; 24, swim bladder; 26, gall bladder; 27, ductus pneumaticus; 28, stomach; 29, intestine; 31, coelomic fat; 32, rib; 33, intercostal musculature; and 34, spleen.
CARR ET AL.—COMPARISON OF CT AND GROSS FISH ANATOMY
187
Figure 8. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 22, liver; 24, swim bladder; 26, gall bladder; 27, ductus pneumaticus; 28, stomach; 29, intestine; 31, coelomic fat; 34, spleen; and 35, pelvic fin musculature.
caudal), and a small region of interest was drawn to measure the Hounsfield units (HU). This was repeated for each organ and performed in each patient separately. The HU value was then averaged for each fish individually and for the group as a whole. Overall the methods employed for the pacu fish yielded excellent imaging detail. The administration of positive contrast into the gastrointestinal tract was only partially successful and did not completely fill the entire tract in all fish. Gonadal tissue was only visible on the CT images in one fish (pacu 2, which was female, based on gross dissection). This fish was used for the initial gross dissection (therefore, transverse gross segments were not available for review). The other two fish were not sexually mature, and therefore sex was not determined at the time of the study; the high standard deviation for the gonadal tissue HU measurements is attributed to the low sample size. Figures 1–11 show the gross and CT images (prior to and after contrast administration, where applicable). Figure 12 is a sagittal reformatted image of a fish with reference lines noting the location of Figures 1–11. Table 1 lists the average HU for each organ that could be measured in these three fish. CT provided good anatomic detail, and there was good correlation between the CT images and the gross specimens. The large amount of intracoelomic fat in these patients provided good contrast with the major organs and clear visualization of the major cardiovascular structures, liver, spleen, kidneys, and gastrointestinal tract. The intracoelomic organs and musculature had HU densities within the expected normal ranges
for soft tissue structures. The CT studies were fast and easy to perform; with sedation it was postulated that these images would be relatively simple to duplicate in live fish using the techniques described in previous studies.1,5,7 Of the diagnostic imaging modalities available for use in fish, CT has distinct advantages over radiography and ultrasound. Given that some fish species have only a small amount of intracoelomic fat, radiographic detail can be poor, and evaluation of the coelom on survey images may be limited to the shape and position of the swim bladder, severely limiting the types of pathology that can be detected.11 Additionally, obtaining orthogonal images in some patients is difficult, as dorsoventral positioning can be challenging as a result of
Figure 9. Comparison of gross (left) and precontrast computed tomography (CT) (right) anatomy. Key: 22, liver; 24, swim bladder; 26, gall bladder; 28, stomach; 31, coelomic fat; 34, spleen; and 36, gonad.
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Figure 10. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 16, descending aorta; 26, gall bladder; 29, intestine; 31, coelomic fat; and 37, posterior kidney.
Figure 11. Comparison of gross (left), precontrast computed tomography (CT) (middle), and postcontrast CT (right) anatomy. Key: 38, urinary bladder; 39, anus; and 40, anal fin musculature.
Figure 12. Sagittal reformatted image of a fish with denotation of the anatomic location of Figures 1–11.
CARR ET AL.—COMPARISON OF CT AND GROSS FISH ANATOMY
Table 1. organs.
Hounsfield units (HU) of intracoelomic
Average HU
Liver Spleen Anterior kidney Posterior kidney Coelomic fat Gonads Gall bladder Epaxial musculature Heart Brain
Standard deviation
83.6 65.4 49.4 46.3 109.2 67.2 29.2 52.1 47.6 37.3
17.6 9.8 2.8 2.0 1.5 38.8 2.3 5.4 3.3 1.6
body morphology.11 Overall, CT limits anatomic superimposition and has superior soft tissue contrast compared to radiography. When compared to ultrasound, CT image acquisition is much faster than the typical ultrasonographic exam and is more repeatable with diminished operator variability. Ultrasound is often limited to coelomic organs, affording incomplete evaluation of the skeletal and cardiovascular organs.11 This current study found that the instillation of positive contrast into the gastrointestinal tract to be a useful technique, but caution is necessary when administering the contrast in order to avoid inadvertent introduction of contrast into the coelomic cavity. It is hoped that the information presented in this article will provide a useful reference both for clinical patients and for further research studies.
LITERATURE CITED 1. Bakal, R. S., N. E. Love, G. A. Lewbart, and C. R. Berry. 1998. Imaging a spinal fracture in a Kohaku koi (Cyprinus carpio): techniques and case history report. Vet. Radiol. Ultrasound 39: 318–321.
189
2. Frank, L. 2009. Digital fish library. http://www. digitalfishlibrary.org. Accessed 26 July 2013. 3. Garland, M. R., L. P. Lawler, B. R. Whitaker, I. D. F. Walker, F. M. Corl, and E. K. Fishman. 2002. Modern CT applications in veterinary medicine. Radiographics 22: 55–62. 4. Gumpenberger, M., O. Hochwartner, and G. Loupal. 2004. Diagnostic imaging of a renal adenoma in a red oscar (Astronotus ocellatus Cuvier, 1829). Vet. Radiol. Ultrasound 45: 139–142. 5. Lewbart, G. A., G. Spodnick, N. Barlow, N. E. Love, F. Geoly, and R. S. Bakal. 1998. Surgical removal of an undifferentiated abdominal sarcoma from a koi carp (Cyprinus carpio). Vet. Rec. 143: 556–558. 6. Lopes, R. B., L. C. Paraiba, P. S. Ceccarelli, and V. Tornisielo. 2006. Bioconcentration of trichlorfon insecticide in pacu (Piaractus mesopotamicus). Chemosphere 64: 56–62. 7. Pees, M., K. Pees, and I. Kiefer. 2010. The use of computed tomography for assessment of the swim bladder in koi carp (Cyprinus carpio). Vet. Radiol. Ultrasound 51: 294–298. 8. Pullela, S. V. S. 1997. Aquaculture of Pacu (Piarctus mesopotamicus) and a Comparison of its Quality: Microbial, Sensory and Proximate Composition. Virginia Polytechnic Institute and State Univ., Blacksburg, Virginia. 9. Rowe, T. Digital morphology. http://www. digimorph.org. Accessed 26 July 2013. 10. Tyson, R., N. E. Love, G. Lewbart, and R. Bakal. 1999. Techniques in advanced imaging of fish. Proc. Am. Assoc. Zoo Vet. 1999: 201–202. 11. Weber, E. P. S., C. Weisse, T. Schwarz, C. Innis, and A. Kilde. 2009. Anesthesia, diagnostic imaging, and surgery of fish. Comp. Contin. Educ. Vet. 31: E1– E9. 12. Weisse, C., E. P. S. Weber, Z. Matzkin, and A. Kilde. 2002. Surgical removal of a seminoma from a black sea bass. J. Am. Vet. Med. Assoc. 221: 280–283. Received for publication 22 May 2013
