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Case Report: Suspected Choledochal Cyst in a DSH cat

Note: This article was published in the Journal of Feline Medicine and Surgery, October 2010: 12 (10)  pp. 814-7.

A nine year old female neutered DSH cat was presented to the referring vet with a history of polyphagia, weight loss and urinating in the house. Her demeanour had also changed, with her becoming nervous and clingy over the previous few days.

Clinical Findings

fig. 1 - lateral radiograph showing displacement of normal viscera

fig. 2 - caudal displacement of viscera by mass

On clinical examination she was quiet but alert and underweight (BCS 2/5). Vital parameters were within normal limits but the mucous membranes were notably jaundiced. In addition, a large, firm, non-painful mass was palpable in the cranial abdomen.

Routine haematology was unremarkable but serum biochemistry revealed moderate elevations in ALT 609(reference range: 0-120)U/l, ALKP 326 (1-170)U/l and bilirubin 118 (0-12)U/l. Significant hypoalbuminaemia was also noted 20 (25-39)g/l.

Conscious radiographs of the abdomen (figs. 1 & 2) revealed a homogenous soft tissue opacity within the cranial abdomen, obscuring and displacing the normal abdominal structures caudodorsally. At this point the cat was referred for further investigations.  Repeat haematology revealed marked leucocytosis 36 (5.5-19.5)x109/l with mature neutrophilia. Serum biochemistry confirmed persistence of the previous findings. Clotting times (PT and APTT) were within normal limits.

fig. 3 — ultrasonograph illustrating large, cystic structure within the cranial abdomen.

fig. 4 - ultrasound of gall bladder

Abdominal ultrasonography revealed a large cystic structure (~10cm diameter) just caudal to the liver. This consisted of a hyperechoic wall of variable thickness containing hypoechoic flocular material (fig. 3).  An additional smaller cystic lesion (~5cm diameter) was noted within the liver parenchyma, consisting of a thicker hyperechoic wall with infolding projections (fig. 4), which was assumed to be the gall bladder.  The abdominal organs were otherwise unremarkable.  Ultrasound-guided needle aspiration of both cystic structures yielded a colourless but slightly cloudy fluid which was submitted for bacteriology cytology and protein assay. This revealed it to be a highly proteinaceous fluid with mixed bacterial growth. No inflammatory or neoplastic cells were found.

Treatment

fig. 5 - intraoperative view inside cyst

The cat was stabilised with medical management; – intravenous fluid therapy and antibiotics (amoxiclav and metronidazole I.V.) prior to exploratory midline coeliotomy. A large, fluid-filled structure was confirmed within the cranial abdomen. This was found to be juxtaposed to the caudal edge of the liver and attached to the common bile duct. The gall bladder was also enlarged and the hepatic and cystic ducts were tortuous and distended. The liver parenchyma was diffusely firm but friable. The pancreas was oedematous. A small stab incision was made in the cyst and suction used to empty it of its contents (fig. 5).  This confirmed the presence of a colourless, slightly cloudy fluid as previously. However, more concentrated, bile-like fluid was also present in the dependant portion of the cyst. The wall of the cyst was thick (~3mm) with the consistency of normal feline small intestine, and appeared to be contiguous with the wall of the common bile duct. Examination within the cyst revealed potential communications with the duodenum distally and the biliary tree proximally.  However, both stomas were small, atresic and could not be catheterised. Given the cyst appeared to arise from the common bile duct, en-mass resection was not considered a viable option. Therefore, subtotal resection of the cyst wall was performed. After closing the stomas at either end with Prolene purse-string sutures, the structure was omentalised;  the original cystostomy incision was partially closed, and the remaining cavity was packed with an omental pedicle.  Interrupted stay-sutures were placed at the stoma to keep the pedicle in place. Inspissated bile was removed from the gall bladder, before the biliary tract was diverted via a standard cholecystojejunostomy.  Biopsies of the pancreas, liver and cyst wall were taken for histopathology.  The abdomen was lavaged with sterile saline and closed in a routine manner.

The cat made an unremarkable recovery from anaesthesia and she remained bright with a good appetite. However, repeat serum biochemistry revealed significant deterioration of her hypoalbuminaemia 13 (25-39)g/L with a concurrent drop in her ionised calcium levels 0.97 (1.20-1.32)mmol/l. Intravenous colloid therapy was instigated to maintain oncotic pressure and serum calcium levels were closely monitored. Over the ensuing days, her albumin levels gradually improved, her serum calcium levels normalised and her bilirubinaemia resolved. Despite persistence of a suboptimal body condition score she continues to make steady clinical improvement.

Histopathology of the cyst wall revealed mature fibrous connective tissue with scattered clusters of well-differentiated glandular structures consistent with bile ducts/ductules. In addition, one of the sections was lined on one side by small, multi-loculated cystic structures covered by a single layer of well-differentiated cuboidal to attenuated epithelial cells. Hepatic and pancreatic sections revealed chronic, active neutrophilic cholangitis with concurrent chronic lymphoplasmacytic pancreatitis respectively.

Discussion

Extra-hepatic solitary cysts of the biliary system are rarely found in dogs and cats. Most cysts are multifocal and linked to polycystic disease, usually affecting the kidneys or liver. In contrast, biliary cystadenomas are often solitary but these are found within the liver parenchyma.2,4

fig. 6a - normal biliary anatomy

Although uncommon, cystic disease of the biliary tract is described in humans. These cystic dilations of the bile duct are referred to as choledochal cysts and usually contain bilious fluid, rich in pancreatic enzymes.1 Most cases are believed to be congenital because they predominantly occur in infants and children. However, approximately 20% are diagnosed in adults. Consequently, several theories for late-onset cyst development have been postulated, including a weakness in the wall of the common bile duct (with or without obstruction distally) and reflux of pancreatic enzymes into the common bile duct due to an anomaly of the pancreaticobiliary junction (i.e. the common bile duct joins the pancreatic duct more proximally than normal giving it similar anatomy to the cat; figs. 6a & b).1 Reflux of pancreatic enzymes is thought to weaken the wall of the common bile duct causing a cyst to form.

fig. 6b - line drawing of surgical findings

Humans often present with signs of biliary obstruction and a palpable mass in the anterior abdomen1. The cysts are divided into five types depending on their anatomical location, Type 1 being the most common and consistent with the findings in the case seen here; a cystic or fusiform dilation of the common bile duct.  Type 5 lesions, saccular dilations of the intrahepatic bile ducts (also known as Caroli’s disease) have been described in a litter of Golden retriever puppies that also had renal cysts.3

Malignant transformation of cyst tissue resulting in carcinoma formation has been described and complete cyst resection is therefore the treatment of choice in human patients.1 In the cat described here a less invasive surgical option, avoiding the need for disruption of the pancreatic duct, was chosen to minimise peri-surgical morbidity. The associated neutrophilic cholangitis and pancreatitis is likely to have resulted from ascending bacterial infection from the intestine. Given these findings, ursodeoxycholic acid and antioxidants (Hepatosyl) were used post-operatively, as well as a continuation of antibiotic therapy. So far the clinical outcome appears to be favourable. However, the long term prospects for the cat remain uncertain and close monitoring for recurrent biliary obstruction and ongoing hepatic and pancreatic disease will be continued.

As far as we are aware, a Type 1 choledochal cyst has not been previously described in the cat. It is possible that the cyst was of congenital origin and that gradual distension eventually culminated in late onset clinical signs due to biliary obstruction and ascending bacterial infection from the intestine. Alternatively, late onset cyst development associated with underlying intestinal, pancreatic or biliary pathology is also a possibility.

References:

1.Besner E., Paddock, H.N., Nguyen L.T., Kay S.M. Choledochal Cyst: A Surgical Perspective. e-medicine review, updated Sept 30 2008

2.Charles J.A., Cullen J.M., Van den Ingh T.S.G.A.M., Van Winkle T., Desmet V.J. Morphological classification of neoplastic disorders of the canine and feline liver. WSAVA Standards for Clinical and Histological Diagnosis of Canine and Feline Liver Diseases Ch9: 117-124

3.Last RD, Hill JM, Roach M, Kaldenberg T. Congenital dilation of the large and segmental intra-hepatic bile ducts (Caroli’s disease) in two Golden retriever littermates. Journal of the South African Veterinary Association 2006 77(4):210-4

4.Van den Ingh T.S.G.A.M. Morphological Classification of Biliary Disorders of the Canine and Feline Liver. WSAVA Standards for Clinical and Histological Diagnosis of Canine and Feline Liver Diseases Ch5: 61-76