An endodermal cyst: the result of a congenital intestinal malformation

Abstract

A midline exploratory laparotomy on a 1-year-old, neutered male, West Highland terrier with a history of lethargy, anorexia, and intermittent vomiting revealed a cranial abdominal cyst. The lining of the excised cyst was histologically identical with that of the small intestine and may have represented an uncommon intestinal malformation.

A 1-year-old, 7-kg, neutered male, West Highland terrier was presented because of intermittent vomiting for the preceding 24 h (day 1). When examined, the dog was depressed, lethargic, and anorexic, and exhibited mild discomfort on palpation of the cranial region of the abdomen. No other abnormal findings were apparent. Differential diagnoses included gastritis due to dietary indiscretion or to a foreign body causing intestinal obstruction. The dog was treated for gastritis with famotidine (Pepcid; Merck Frosst, Kirkland, Quebec), initially 0.8 mg/kg bodyweight (BW), IV, followed by 1.4 mg/kg BW, PO, q12h for 4 d. The owner was instructed to withhold food and water for 24 h and then to begin feeding small amounts of water and a bland diet.

On day 3, the dog was returned to the clinic because of continued lethargy and anorexia. Physical examination revealed mild depression, slight hypothermia (37.9°C), and approximately 8% dehydration. Heart rate, capillary refill time, and respiratory rate were within normal limits. Differential diagnoses included gastritis, gastric ulcer, pancreatitis, and intestinal obstruction. A urine sample was submitted for urinalysis, and a blood sample for a complete blood cell (CBC) count and a biochemical profile. Plain abdominal radiographs were taken, followed by left lateral and dorsoventral radiographs at 15-min intervals after administration of contrast medium (Hypaque-M; Sanofi Winthrop, Markham, Ontario), 2.5 mL/kg BW, PO.

Results from the CBC count and urinalysis were unremarkable. Serum biochemical results indicated mild hypochloremia (chloride 95 mmol/L; reference range, 101 to 119 mmol/L), consistent with loss due to vomiting. The plain abdominal radiographs revealed a large, gas-distended stomach. The upper gastrointestinal contrast radiographs confirmed an enlarged stomach with a roughened mucosa. The sequential contrast radiographs indicated delayed gastric emptying and prolonged small intestinal retention time.

On the basis of contrast radiography, the tentative diagnosis was gastritis and gastric ulceration. The dog was hospitalized and treated with electrolytes (Plasmalyte 148; Baxter Corporation, Toronto, Ontario) at a rate of 72 mL/h, IV, reduced to 27 mL/h after 4 h. Sucralfate (Sulcrate; Hoechst Marion Roussel, Laval, Quebec), 14 mL/kg BW, PO, and metoclopramide (Reglan; Wyeth-Ayerst, St. Laurent, Quebec), 0.35 mg/kg BW, SC, were administered q8h. As the dog remained anorectic the following morning (day 4) and vomited 1 h after forced feeding, both sucralfate and metoclopramide treatments were continued q8h.

Vomiting continued on day 5, and a midline laparotomy was performed. A large fluid-filled structure (8 cm in diameter) was discovered cranial to the pylorus, between the common bile duct and the lesser curvature of the stomach. A syringe was used to remove 75 mL of a green-brown fluid from the structure. Possible differential diagnoses were a choledochal or an omental cyst. After incision and drainage, the cyst was marsupialized to the body of the stomach. Recovery was uneventful, and the dog was discharged on day 6.

On the evening of day 6, the dog had become recumbent and weak, and exhibited discomfort when handled. When examined at an emergency clinic, the dog had pale mucous membranes and was moderately hypothermic (36.6°C). Postoperative hypothermia was diagnosed, and the dog was treated with electrolytes (Plasmalyte-148; Baxter Corporation), 18 mL/h, IV, and warmed. Oxymorphone (Numorphan; Dupont Merck Pharma, Vaughan, Ontario), 0.1 mg/kg BW, IV, and ampicillin, 15 mg/kg BW, IV, were administered. The dog was hospitalized at the original clinic and was closely monitored during days 7 and 8. The dog's appetite improved; however, 2 episodes of vomiting occurred. The dog was discharged on day 9, and no further vomiting was observed between days 9 and 13, when the dog was reexamined. On day 13, the dog was bright and responsive, and was reported to be very active with a voracious appetite.

The dog returned to the clinic on day 28 because of repeated vomiting during the preceding 24 h. Appetite and bowel movements were normal. The dog was bright and responsive, and no abnormal findings were apparent. The possibility of recurrence of the cyst was considered. Intermittent vomiting continued for the next 5 d.

On day 33, a 2nd exploratory surgery was conducted. Many adhesions had formed between the liver, duodenum, and stomach. Blunt dissection between the liver and stomach exposed a cystic structure that was fibrotic and contained little fluid. Two ligatures were tied around the cranial margin of the cyst, where it appeared to be arising from the tip of the left middle lobe of the liver. The area between the ligatures was incised, freeing the cranial aspect of the cyst, which then was bluntly dissected from the surrounding tissues, caudally, to its point of marsupialization on the stomach. The structure was then resected from the stomach, placed in 10% buffered formalin, and submitted for histopathologic examination. During resection, it was apparent that fibrosis from the marsupialization had caused partial pyloric occlusion, so a Y-U pyloroplasty was performed. Postoperative pain was controlled with morphine (Morphine sulfate injection USP; Sabex, Boucherville, Quebec), 0.35 mg/kg BW, IM, and ampicillin, 20 mg/kg BW, IV, q6h, was administered. The dog recovered well and the excision was considered curative. One year postoperatively, the animal was healthy, with no recurrence of symptoms.

Histopathologic examination indicated that the cystic structure had a lining identical with that of the small intestine; that is, a single simple columnar layer of epithelium, attenuated in areas where it had become stretched. Beneath this was a submucosal layer that was surrounded by a layer of smooth muscle identical with muscularis mucosa. While there was extensive fibrous tissue deposition and early granulation tissue, no significant inflammation existed. As this structure existed in isolation and not as a diverticulum of the small intestine, it was best described as an endodermal cyst. However, other less likely differential diagnoses that must be considered include omental cyst, choledochal cyst, or pancreatic pseudocyst. Classification of such structures is based on the histological appearance of the cyst lining and wall.

Omental cysts form when abnormalities in omental lymphatic tissue cause obstruction of lymphatics (3). Such cysts do not share a wall with the intestine (3). In humans, they may be either congenital or traumatic and usually cause no clinical signs (3). While an omental cyst was included in the list of differential diagnoses, histopathologic examination did not support this diagnosis, as the walls of omental cysts have no muscular layer (3).

Choledochal cysts probably originate from an embryologic weakness in the bile duct wall (3). Generally, dilation of the common bile duct occurs proximal to the cyst, while distally it is narrower (3). While the cystic structure in this case appeared intimately associated with the biliary tree, it was not part of the common bile duct. In human patients, these cysts often present clinically as a triad of pain, jaundice, and a mass in the right upper quadrant of the abdomen (3). In this case, jaundice did not occur and serum bilirubin was not elevated. Finally, choledochal cysts have little or no epithelial lining and are generally composed of fibrous tissue with occasional smooth muscle or elastic fibers (3).

Pancreatic pseudocysts are also reported in dogs and humans. Affected dogs display anorexia, depression, vomition, and pyrexia (4). In humans, these cysts are a common complication of acute pancreatitis (5). They are generally located in the dorsal part of the abdominal cavity, adherent to the stomach and some distance away from the parietal wall (4,5). The endodermal cyst in this case did not adhere to the stomach. Furthermore, pseudocysts consist of a fibrous sac without an epithelial lining (4,5).

This endodermal cyst, found in close association with the duodenum, biliary tree, and pyloric portion of the stomach, most likely represents a congenital foregut intestinal malformation that may have arisen by enteric duplication or as a diverticulum of the foregut (6). Almost all duplications are caused by failure of normal recanalization; as a result, 2 lumina form (1,6). Duplications are a rare developmental malformation in humans and are uncommon in animals (1,7). They generally occur as juxtaintestinal, cyst-like formations on the mesenteric side of the intestine (1,6,7). General characteristics include fusion between the wall of the duplication cyst and the adjoining segment of the intestinal tract, a shared tunica muscularis between the cyst and the adjoining normal bowel, and a similar or heterotopic epithelial lining of the lumen of the cyst (6,7). The cyst in this case did not lie on the mesenteric side of the intestine, nor was it intimately associated with the duodenum. It seems more likely that the cyst originated from a true intestinal diverticulum. In order to become an isolated structure, this diverticulum must have undergone stenosis at its origin, becoming discontinuous with the lumen of the gut.

Intestinal diverticular malformations are rare congenital anomalies that occur in the small intestines of dogs and cats and cause clinical signs, most frequently vomiting (2), as in this case. In contrast, human intestinal diverticula seldom cause clinical disease and are more often reported as an incidental finding at autopsy (8,9).

The endodermal cyst in this case may have developed with the liver and the pancreas, to which it was closely associated. Embryologic diverticuli arise from the foregut (6). The hepatic diverticulum is the primordium of the liver; gall bladder; and biliary duct system, and the pancreas is formed by fusion of the dorsal and ventral pancreatic buds, which originate from the endodermal lining of the foregut (6).

Regardless of its exact origin, the endodermal cyst probably originated either directly or indirectly from the foregut, from which it became separated because of stenosis at its point of origin. The epithelial lining continued to secrete, resulting in fluid accumulation and a cystic enlargement. The dog was asymptomatic until the size and location of the cyst resulted in compression of adjacent structures (2). Vomiting occurred due to pyloric occlusion.