History

An 11.5-year-old spayed female Cocker Spaniel (dog 1) that had an episode of immune-mediated thrombocytopenia 4 months previously was reevaluated at the North Carolina State University Veterinary Teaching Hospital. When first examined, the dog had severe thrombocytopenia, anemia, melena, and hematuria; treatment with prednisone, azathioprine, aspirin, and famotidine was initiated. At the recheck examination, the dog had soft stools and was urinating normally with no signs of hematuria; however, hepatomegaly was detected during physical examination.

Additionally, a 6-year-old castrated male Shetland Sheepdog (dog 2) was evaluated because of sudden onset of vomiting and anorexia. Clinicopathologic analyses performed by the referring veterinarian revealed markedly high liver enzyme activities (alkaline phosphatase, > 2,000 U/L [reference interval, 23 to 212 U/L]; alanine aminotransferase, 832 U/L [reference interval, 10 to 100 U/L]; and γ-glutamyltransferase, 38 U/L [reference interval, 0 to 7 U/L]) and bilirubin concentration (5.6 mg/dL; reference interval, 0 to 0.9 mg/dL).

Clinical and Gross Findings

At the recheck examination of dog 1, a serum biochemical panel revealed slight hypoalbuminemia, mild hypercholesterolemia, mild hyperbilirubinemia, markedly high alkaline phosphatase activity (3,088 U/L; reference interval, 16 to 140 U/L), moderately high alanine aminotransferase activity (381 U/L; reference interval, 12 to 54 U/L), and markedly high γ-glutamyltransferase activity (132 U/L; reference interval, 0 to 6 U/L). Abdominal ultrasonography revealed markedly hyperechoic and hyperattenuated cranial abdominal mesentery with trace peritoneal fluid around the stomach and liver near the gallbladder. The gallbladder wall measured 7.5 mm at its thickest point. A crescent-shaped hypoechoic rim (thickness, 9.0 mm) surrounded the gallbladder and conformed to the margins of the gallbladder and the borders of the liver. Differential diagnoses for the hypoechoic rim included inflammation or edema of the liver in the area close to the gallbladder or a focus of echogenic fluid dissection between the gallbladder and liver. The duodenal papilla could not be identified because of gas shadowing in the duodenum. Smears of a fine-needle aspirate sample of peritoneal fluid were prepared and stained with Wright-Giemsa stain. A preliminary microscopic examination revealed bright blue to blue-gray smooth material prominently arranged in long, dense, linear strands, some of which had a fibrillar appearance (Figure 1).

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Photomicrographs of smears prepared from peritoneal fluid aspirate samples collected from a dog that was undergoing a recheck examination following an episode of immune-mediated thrombocytopenia (dog 1; A) and a dog that was evaluated because of sudden onset of vomiting and anorexia (dog 2; B). In the smear from dog 1, large amounts of bright blue to blue-gray amorphous material are prominently arranged in long, dense, linear strands with a fibrillar-like appearance. In the smear from dog 2, the same type of material is evident but more inflammatory cells are present in the background. In both panels, Wright-Giemsa stain; bar = 100 μm.

Citation: Journal of the American Veterinary Medical Association 239, 1; 10.2460/javma.239.1.65

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For dog 2, abdominal ultrasonography was performed and a moderate volume of peritoneal fluid and diffusely hyperechoic mesentery were observed. There were formed gallbladder contents characterized by hyperechoic striations. Gallbladder margins were irregular with surrounding regions of hyperechogenic mesentery and hyperechoic hepatic tissue. Smears of a fine-needle aspirate sample of peritoneal fluid were prepared and stained with Wright-Giemsa stain. A preliminary microscopic examination revealed clumps of amorphous blue to blue-gray material, often in a linear arrangement (Figure 1).

Cytologic Findings

For dog 1, only direct smears of the aspirated peritoneal fluid sample were submitted. The specimen was mildly hemodiluted and consisted primarily of bright blue to blue-gray smooth material that was prominently arranged in long, dense, linear strands, some of which had a fibrillar appearance. There were moderate numbers of well-preserved to slightly degenerate neutrophils adjacent to the thick strands and occasionally admixed with thinner clumps of the material. No microbial agents were evident. The interpretation was extracellular smooth linear material with moderate suppurative inflammation; the specimen was most likely peritoneal bile, although aspiration of a cystic lesion or a secretory material from a nonexfoliative neoplasm could not be completely excluded. Submission of free fluid for bilirubin measurement was recommended to determine whether the cytologic findings were consistent with bile peritonitis.

For dog 2, direct smears of the aspirated peritoneal fluid sample were highly cellular and consisted of clumps of amorphous blue to blue-gray material, often in a linear arrangement. There were also inflammatory cells present, and a differential count revealed 76% slightly degenerate neutrophils and 24% activated macrophages. The cytologic findings were very similar to those for dog 1. Some of the peritoneal fluid sample was tested^a for bilirubin and yielded a positive result.

Histopathologic Findings

On the basis of the ultrasonographic and cytologic findings, an exploratory laparotomy was performed in each dog. Both dogs had a ruptured gallbladder. In dog 1, the bile was described as a thick, dark paste. Chole-cystectomies were performed in both patients, and the gallbladders were submitted, together with liver biopsy specimens, for histologic examination.

For both dogs, gross examination of the gallbladder revealed moderate to marked distention with luminal mottled yellow to dark green, viscous to gelatinous material and multifocal to coalescing serosal hemorrhage. Histopathologic findings were similar in both cases and included regions of hemorrhage and suppurative inflammation within the wall of the gallbladder, epithelial and submucosal necrosis and hyperplasia, hyperplastic cyst formation, and distention of the lumen of the gallbladder by a large amount of acellular, homogeneous, laminated to finely granular, pale basophilic material (Figure 2).

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Photomicrograph of a section of the gallbladder that was removed from dog 1. Notice that the gallbladder wall is markedly distended and disrupted by hemorrhage and pyknotic debris and that there are areas of necrosis. The lumen is markedly distended by abundant, finely granular, pale basophilic and eosinophilic material. H&E stain; bar = 100 μm.

Citation: Journal of the American Veterinary Medical Association 239, 1; 10.2460/javma.239.1.65

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For dog 1, examination of the liver biopsy specimen revealed acute, severe, multifocal to coalescing, hepatic necrosis of the tissue adjacent to the gallbladder and acute degeneration of biliary epithelium and moderate to severe hepatic atrophy and fibrosis with biliary proliferation. For dog 2, examination of the liver biopsy specimen revealed moderate biliary hyperplasia, neutrophilic cholangitis, and periportal bridging fibrosis.

Cytologic and Histologic Diagnosis

Gallbladder mucocele rupture, bile peritonitis, cholestasis, and liver inflammation and necrosis (dogs 1 and 2).

Comments

The material in the peritoneal fluid aspirate samples collected from both dogs of this report was considered to be bile released from the gallbladder as a result of rupture caused by a mucocele. The interesting finding in these cases was the abundance of blue (Wright-Giemsa–stained) material in the peritoneal fluid samples, which did not have the characteristics that are often described for the cytologic appearance of peritoneal fluid samples collected from animals with bile peritonitis, namely tan to light brown to blue-green pigment and bilirubin crystals free in the background or engulfed by macrophages.^1–3 Furthermore, the material did not have the characteristics of what has been termed as white bile in human medicine and, in dogs, what has been described cytologically as an acellular, mucinous blue-staining material that is found in the abdominal cavity as a result of a tear in the common bile duct.¹ In the dogs of this report, the stained material had prominent linear formations with discrete borders, a bright blue color, and a smooth to fibrillar texture rather than a mucinous type of appearance. It is possible that this appearance is unique to a ruptured biliary mucocele.

A mucocele is a distention of a cavity caused by an accumulation of mucus.^3–5 The mucoid material in gallbladder mucocele is generally described grossly as a green-black, bile-laden, semisolid to immobile mucoid mass.⁶ It has also been described as a thick, viscous, brownish mass that fills the gallbladder.⁵ Histologically, the mucoid material appears as a mass of acellular, homogeneous, laminated, basophilic material.⁷ The accumulation of material is due to cystic hyperplasia of the mucus-producing cells of the gallbladder.⁴ The primary cause for mucin accumulation is unknown, but predisposing factors, including decreased gallbladder motility, biliary stasis, and altered absorption of water from the gallbladder, are hypothesized to contribute to the formation of biliary sludge (a mixture of cholesterol crystals, precipitated bile pigments, and bile salts). It is possible that the sludge is a precipitating factor for the formation of the mucocele.⁴ Biliary mucoceles typically develop in older dogs,⁵ and there may be genetic predisposing factors because this disease appears to be more prevalent in some breeds, including Cocker Spaniels, Shetland Sheepdogs, and Miniature Schnauzers.^3,4 A mucocele produces pressure and induces necrosis of the gallbladder wall, which ultimately lead to rupture and peritonitis. If bacteria are present in the bile, the prognosis is worse. Bile-laden mucus may also extend into the cystic, hepatic, and common bile ducts, resulting in variable degrees of extrahepatic biliary obstruction.⁸

Prompt diagnosis of bile peritonitis is very important. Delayed treatment results in higher morbidity and mortality rates, especially if sepsis is present, which could develop following bacterial translocation from the gastrointestinal tract. If the cause of the peritonitis is a mucocele, removal of the gallbladder is the recommended procedure. Although bile peritonitis can often be diagnosed cytologically, it is important to consider that sometimes the characteristics of the material in a peritoneal fluid aspirate sample can differ from what is traditionally described. When possible, bilirubin concentration in a peritoneal fluid aspirate sample should be determined and compared with the patient's plasma bilirubin concentration to confirm the diagnosis,^9,10 a procedure that was not possible for dog 1 of this report because a sample of free fluid was not submitted. Clinical signs of bile peritonitis in dogs are not specific (eg, lethargy, anorexia, and signs of abdominal pain) but together with other common serum biochemical findings, including high concentration of bilirubin and high activities of alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, and γ-glutamyltransferase, can aid in the diagnosis.^1,2,8