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Figure 1—Lateral (A) and ventrodorsal (B) radiographic views of the abdomen of a 3-year-old sexually intact female North American beaver (Castor canadensis) evaluated because of lethargy and a bloated appearance.
History A 3-year-old sexually intact female North American beaver (Castor canadensis) owned by a local zoo was found passively floating in the pool; it was unable to stand and appeared depressed. The beaver had been previously healthy, and none of the other beavers in the enclosure had any signs of illness. The beaver appeared to have an adequate nutritional status. No abnormalities were found on physical examination, aside from a bloated appearance and lethargy. There was no history or physical evidence of trauma. No definitive abnormalities were found on hematologic evaluation (Hct, WBC count, and total platelet count) and serum biochemical analysis (total protein, albumin, BUN, and creatinine concentrations), when compared with values published for this species.1,2 Abdominal radiographs were obtained (Figure 1). Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page → This report was submitted by Eric T. Hostnik, DVM, and Silke Hecht, Dr med vet; from the VCA South Shore Animal Hospital, 595 Columbian St, South Weymouth, MA 02190 (Hostnik); and the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996 (Hecht). Dr. Hostnik’s present address is Department of Radiology, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210. Address correspondence to Dr. Hecht (
[email protected]). JAVMA, Vol 246, No. 2, January 15, 2015
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Figure 2—Same radiographic images as in Figure 1. A generalized decrease in serosal margin detail, consistent with abdominal effusion, steatitis, or peritonitis, is evident. The small intestines are diffusely dilated with gas (arrowheads), consistent with paralytic ileus. The stomach is distended with a mixture of soft tissue or fluid opacity and gas (arrows). Multiple, small, amorphous gas opacities along the ventral aspect of the abdominal wall overlying the ventral margin of the stomach (asterisk) most likely represent free abdominal air (pneumoperitoneum) or gas inclusions in the gastric wall due to gastric wall necrosis or extensive ulceration.
Diagnostic Imaging Findings and Interpretation A generalized decrease in serosal margin detail, consistent with abdominal effusion, steatitis, or peritonitis (Figure 2), is evident. The small intestines are diffusely dilated with gas, and the stomach is distended with a mixture of soft tissue or fluid opacity and gas. The large intestine is displaced and obscured by dilated small intestinal segments, and no obvious large intestinal abnormalities are detected. Multiple, small, amorphous gas opacities along the ventral aspect of the abdominal wall overlying the ventral margin of the stomach are evident, most likely representing free abdominal air (pneumoperitoneum) or gas inclusions in the gastric wall due to gastric wall necrosis or extensive ulceration. Paralytic ileus was the top differential diagnosis for generalized, severely dilated intestinal loops. Mesenteric torsion was considered unlikely because of concurrent gas distension of the stomach and because an even more severe degree of intestinal distension is usually observed in cases of mesenteric torsion. With no recent history of surgery and no history of blunt force trauma, bacterial septic enteritis or peritonitis was considered the most likely underlying cause of distension of the gastrointestinal track. Possible underlying causes of spontaneous pneumoperitoneum in this patient included gastrointestinal perforation or bacterial peritonitis. Treatment and Outcome Because of the suspicion of free peritoneal gas or gastric wall necrosis, exploratory laparotomy was 186
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immediately performed via a standard midline approach. Extensive diffuse peritonitis was identified, and the stomach and small intestine were severely diffusely distended and discolored and lacked motility. The beaver was euthanized because of the poor prognosis and anticipated difficulty of intensive medical care in this nondomestic patient. Necropsy revealed fibrin strands in the peritoneal cavity, uniform gaseous distension of the gastrointestinal tract, extensive ulceration and erosion of the gastric mucosa, discoloration (dark red to gray) of the jejunum, and necrotizing colitis. Histologic examination identified surface bacteria associated with the gastric lesions, intralesional bacteria within the colon, acute diffuse fibrinous pneumonia, and acute diffuse periportal hepatitis and cholangitis. A final diagnosis of bacterial gastroenteritis with septicemia was made. Comments Aside from radiographic suspicion of pneumoperitoneum or gastric wall necrosis, paralytic (functional) ileus was the most striking finding in this patient. This condition is characterized by vascular or neuromuscular abnormalities within the intestinal wall resulting in cessation of peristaltic contractions. Although overlap with radiographic findings in obstructive ileus exists, paralytic ileus should be the primary consideration if there is extensive uniform rather than focal intestinal dilation.3 It is unknown whether the paralytic ileus was caused by septicemia or the sepsis was secondary to the ileus in this patient. The pathogenesis of paralytic ileus is still debated. Paralytic ileus is believed to result from the JAVMA, Vol 246, No. 2, January 15, 2015
activation of inhibitory neural reflex pathways and activation of inflammatory processes.4 Septic shock can severely impair gastrointestinal function. The stagnant state of the gastrointestinal tract causes an excessive accumulation of bacteria within the intestines, and the buildup of bacteria within the compromised intestinal wall is thought to contribute to translocation of bacteria.5 Studies6 in mice have shown that IV infusions of septic lymph fluid decrease both small intestinal and colonic motility. The decision for exploratory laparotomy in this patient was driven by the suspicion of free abdominal gas or gastric wall necrosis. Gas inclusions in the gastric wall (gastric pneumatosis) seen in dogs with gastric dilation and volvulus only have a positive predictive value of 41% for gastric wall necrosis, whereas incidental gas inclusions seen in the rest of the patient population were attributed to gas under pressure being forced into the submucosal tissues through a mucosal breach.7 However, considering that our patient did not have evidence of gastric dilation and volvulus or gastric outflow obstruction, gas accumulation in the gastric wall was felt to be secondary to necrosis rather than increased intragastric pressure and therefore clinically relevant. Fur-
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ther imaging such as abdominal ultrasonography or horizontal beam radiography could have been considered to confirm or rule out free abdominal gas, further evaluate the gastrointestinal tract, and obtain samples of abdominal effusion. 1. 2. 3. 4. 5. 6.
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Kitts WD, May CR, Stephenson B, et al. The normal blood chemistry of the beaver (Castor canadensis) A. Can J Zool 1958;36:279–283. Stevenson AB, Kitts WD, Wood AJ, et al. The normal blood chemistry of the beaver (Castor canadensis) B. Can J Zool 1959;37:9–14. Riedesel EA. The small bowel. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 6th ed. St Louis: Elsevier Saunders, 2013;789–811. De Winter BY. Study of the pathogenesis of paralytic ileus in animal models of experimentally induced postoperative and septic ileus. Verh K Acad Geneeskd Belg 2003;65:293–324. Dowling PM. Motility disorders. In: Silverstein DC, Hopper K, eds. Small animal critical care medicine. St Louis: Elsevier, 2009;562–565. Königsrainer I, Turck MH, Eisner F, et al. The gut is not only the target but a source of inflammatory mediators inhibiting gastrointestinal motility during sepsis. Cell Physiol Biochem 2011;28:753–760. Fischetti AJ, Saunders HM, Drobatz KJ. Pneumatosis in canine gastric dilatation-volvulus syndrome. Vet Radiol Ultrasound 2004;45:205–209.
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