Severe gastric impaction secondary to a gastric polyp in a horse

Abstract

A 13-year-old Percheron gelding was presented for refractory gastric impaction. At necropsy a pedunculated 10 cm × 11 cm × 14 cm mass, histologically identified as an inflammatory polyp, was suspected to have been partly obstructing the pylorus. This is the first report of a polyp resulting in gastric outflow obstruction in a horse.

Case description

A 13-year-old Percheron gelding was presented to the Ontario Veterinary College Health Sciences Centre (OVC-HSC) for a refractory gastric impaction. The gelding had a 6-month history of inappetence and weight loss. Over this period the gelding had been treated at home by the primary care veterinarian with various courses of antimicrobials, anti-inflammatory drugs, and gastroprotectants with minimal effect. The week prior to referral the horse was diagnosed with a gastric impaction via gastroscopy at another hospital. A complete blood cell count and serum biochemistry profile performed by the referring veterinarian at that time was unremarkable. Treatment with oral fluids, mineral oil, dioctyl sodium sulfosuccinate, and cola over several days failed to improve the animal’s clinical condition. The horse began to show signs of mild abdominal discomfort, and was, therefore, referred to the OVC-HSC.

On presentation, the gelding was dull and quiet. The horse had a body condition score of 1.5/5 with a significant reduction in fat stores and muscle mass. Heart rate, respiratory rate, and rectal temperature were within reference ranges. Mucous membranes were tacky, and skin tent was prolonged. Clinical dehydration was estimated to be 7% to 8%. Gastrointestinal sounds were significantly reduced and fecal production was scant. Digital pulses were present but mild in all 4 feet with no heat or lameness detected. There was no response to hoof testers on any foot. Venous blood gas indices (including pH, pO₂, pCO₂, BE, and HCO₃) and serum electrolyte levels (including Na⁺, K⁺, Cl⁻) on admission were unremarkable. Packed cell volume was increased at 51% (reference range: 31% to 48%); however, total plasma solids were within normal reference limits.

The gelding was treated aggressively with intravenous lactated Ringer’s solution at 4 mL/kg body weight (BW) per hour (Baxter, Mississauga, Ontario), 5 L tap water q4h, PO via an indwelling nasogastric tube; omeprazole (Gastrogard; Mérial Canada, Baie d’Urfé, Quebec), 4 mg/kg BW, q24h, PO, and flunixin meglumine (Banamine; Schering-Plough Animal Health, Pointe Claire, Quebec), 1.1 mg/kg BW, IV, q24h. The gelding was offered small amounts of a variety of feeds to help stimulate gastric motility, but the horse was completely anorexic. Parenteral nutrition supplementation was considered but not instituted at that time due to being too costly.

Gastroscopy was performed 60 h following admission to the hospital using a 3-m flexible video endoscope (3.0 m Gastroscope SIF-140; Olympus America, Centre Valley, Pennsylvania, USA). A large concretion of feed material was still present in the stomach, which obscured visualization of the glandular mucosa and a large portion of the pars esophagea. A large, irregular fleshy mass was observed but the origin could not be determined due to the size of the impaction. Based on the suspected chronicity of the gastric impaction, lack of response to treatment, and the presence of a large mass of unknown origin in the stomach, the prognosis for recovery was considered poor to grave, and the horse was euthanized.

At postmortem examination, the stomach was enlarged to approximately 4 times normal size, primarily due to dilation of the pars esophagea, and contained large quantities of firm, dry fibrous feed material (Figure 1). A single ulcerated pedunculated mass approximately 14 cm × 11 cm × 10 cm in size was identified arising from the squamous mucosa, 1 cm from the margo plicatus, on an 8 × 30 mm stalk (Figure 2). Additionally, there was multifocal-to-regionally extensive ulceration of approximately 30% of the gastric pars esophagea, associated with 3- to 4-fold fibrous thickening of the gastric wall. No other significant abnormalities were detected at necropsy.

Figure 1.

Impaction of the stomach with dry, firm, and fibrous feed material. The stomach is dilated to approximately 4 times the normal size.

Figure 2.

A single ulcerated pedunculated mass (approximately 14 cm × 11 cm × 10 cm) arising from the squamous mucosa, 1 cm from the margo plicatus.

Tissues were collected and fixed in 10% neutral buffered formalin, further dissected and embedded in paraffin wax. Sections (4 μm) were mounted on silane-treated glass slides and stained with hematoxylin and eosin (H&E).

Histopathological examination revealed that the gastric mass was composed of numerous, thick, concentric layers of fibrin, large numbers of neutrophils and eosinophils, and fewer macrophages, lymphocytes, and plasma cells (Figure 3). Numerous, large mixed colonies of Gram-negative, bacterial rods and cocci were scattered throughout the superficial fibrin layers. The deeper layers of the mass consisted of large amounts of progressively maturing granulation tissue that extended from deep within the submucosa into the pedunculated mass, forming a 700- to 850-μm dense fibrous stalk. There was diffuse ulceration of the overlying surface epithelium extending to within 40 μm of the origin of the stalk. The remaining epithelium at the base of the stalk and the adjacent gastric mucosa were markedly thickened, approximately 4- to 5-fold, and hyperplastic, often forming short 20- to 30-μm blunt projections extending into the lamina propria. Based on these findings and the absence of histological evidence of a neoplastic process the mass was identified as an inflammatory polyp.

Figure 3.

Inflammatory polyp consisting of eosinophils, neutrophils, and lymphocytes. 60× magnification. H&E stain.

Discussion

This case describes an unusual etiology for a primary gastric impaction in an adult horse, likely associated with an outflow obstruction due to a large inflammatory polyp. A gastric impaction is described as a concretion of ingesta that precludes visualization of the margo plicatus and remains in the stomach despite a minimum 16 hours of fasting (1). Gastric impactions are considered primary if they result from a pathophysiological disturbance in gastrointestinal motility related to altered motility patterns, abnormal gastric secretion, or functional gastric outflow obstructions (2). Secondary gastric impactions arise from ingestion of expandable feed stuffs, persimmon fruits, dental disease, or inadequate water intake, resulting in impaired gastric emptying due to the gastric content itself, despite otherwise normal gastric function (3,4). Primary gastric impactions in horses are reported sporadically in the literature (1,5). Gastric impactions have been reported in numerous other species including cattle (6), buffalo (7), cats (8), swine (9), and sperm whales (10).

A recent retrospective study reviewed the clinical examination findings, diagnostics, and treatment of 20 horses with primary gastric impaction (1). Similar to the case described here, inappetence was the predominant presenting complaint with signs of chronic or acute colic occurring in over half of the cases. The initial diagnosis of a gastric impaction was based on finding a large bolus of ingesta which restricted visualization of the margo plicatus following 24 h of fasting. This diagnosis was confirmed following aggressive parenteral and enteral fluid therapy and 60 h of fasting. However, it has been suggested that the only definitive method to diagnose a gastric impaction in a horse is exploratory abdominal surgery during which the stomach can be palpated (2). Direct surgical access to the equine stomach for the purpose of relieving the obstruction, however, is rarely possible, which is one reason gastrotomy was not considered in this case. Certain abnormalities may be found on palpation per rectum in cases of severe gastric distension, including displacement of the spleen or parts of the large intestine (2); however, these findings are not consistent or specific.

Aggressive fluid therapy was used in this case in an attempt to soften the mass of ingesta and potentially aid in passage of the feed material. Gastric lavage was attempted on numerous occasions; however, no fluid or feed material could be retrieved. Enteral fluid therapy alone or in combination with mineral oil or magnesium sulfate has been used to successfully resolve primary gastric impactions (1,5). In the retrospective study by Vainio et al (1), the gastric impactions in 18 of 20 horses were resolved using various quantities of enteral fluids (2 to 10 L every 2 h) and laxatives over 1 to 5 days. The time from onset of clinical signs to hospitalization and treatment ranged from 1 d to 6 mo (median 3 d). In the case reported here, the horse had a history of inappetance for at least 6 mo, although the duration of the gastric impaction was unknown. Based on the prolonged history and the marked dilation of the stomach seen at necropsy it is feasible that the impaction had been present for months. To the authors’ knowledge, there are no cases of successful resolution of longstanding gastric impactions in horses reported in the veterinary literature. Although the use of laxatives for the treatment of gastric impactions in horses has been reported (1), there does not appear to be any conclusive evidence that supports the effectiveness of laxatives in most cases. Mineral oil does not penetrate impacted feed material and therefore its use is not warranted in these cases. Cola is often administered in humans and horses with gastric impactions secondary to persimmon fruit ingestion with variable effect (3–5,11–13). The acidity and carbonation of the cola are thought to break down the fibers and tannins of the persimmon bezoar (11,12). The effectiveness of cola for treating other types of gastric impactions, as in this case, remains questionable.

Gastric masses in horses are most commonly neoplastic in origin. Squamous cell carcinoma was the most common of all gastric neoplasms reported by Taylor et al (14) in a cohort of 24 horses, with smaller numbers of leiomyoma, mesothelioma, adenocarcinoma, and lymphoma. Clinical presentation of gastric tumors is non-specific and may include a history of inappetance, weight loss, lethargy, and colic (14). These neoplasias can range from diffuse, irregular proliferations of the squamous mucosa to single, discrete masses similar to the polyp described in this case (14). All of the horses with endoscopically confirmed gastric masses in the cohort reported by Taylor et al (14) were euthanized or died shortly after diagnosis. Gastric polyps are routinely found as clinically important lesions in 2% to 3% of all gastroscopic examinations in humans (15). A gastrointestinal polyp is defined as a lesion which is elevated above the surrounding mucosa, is non-neoplastic, and is considered an incidental finding in most patients (15,16). However, gastric polyps may result in delayed gastric emptying and gastrointestinal bleeding (15,16). Inflammatory fibroid polyps are typically located deep within the mucosa and surrounding submucosa and are composed of loose connective tissue, reticular fibers, and eosinophilic infiltrate (15,16). This is similar to the composition of the polyp found in this case, except that instead of an intramural mass the polyp was definitively pedunculated. Gastric polyps are uncommonly reported in dogs and are considered benign and an incidental finding during gastric endoscopy or necropsy (17). In the present case, the stalk of the polyp was relatively close to the cardia, which allowed for visualization of the mass on gastroscopy prior to euthanasia. Based on the position of the mass relative to the bulk of the impacted feed material, it was suspected that the mass may have acted as a ball valve, causing chronic intermittent obstruction of the pylorus which may have contributed to the initial development of the impaction. However, it is also possible that a primary gastric impaction may have lead to chronic inflammation of the stomach wall and subsequent development of the polyp, which then simply exacerbated the pre-existing problem. Gastric outflow obstructions have been associated with large gastric polyps in the pyloric antrum in dogs (18).

There is a single case report in the equine veterinary literature which describes a gastric polyp in a 13-year-old Arabian gelding (19). The horse was presented with acute signs of abdominal discomfort, abdominal distension, and peritonitis. A gastrotomy revealed a large pedunculated mass arising from the pylorus resulting in complete obstruction of the proximal duodenum. The mass was histologically confirmed as a hyperplastic polyp being composed entirely of hyperplastic pyloric mucosa. This report differs from the present case with respect to presentation of clinical signs, location of the polyp, and the histological composition of the polyp. This case report is the first to describe a gastric impaction associated with an inflammatory polyp in a horse.

In conclusion, primary gastric impactions resulting from outflow obstructions are uncommon in the horse. However, a gastric impaction resulting from primary or secondary etiology should be considered as a possible differential diagnosis in patients with a prolonged history of partial to complete anorexia. Gastroscopy, a simple and relatively non-invasive procedure, may aid the clinician in the diagnosis of a gastric impaction. Gastric masses can result in gastric impactions in the horse, but this is rare. The majority of gastric masses are neoplastic in origin, but this should be confirmed by biopsy. Treatment of chronic gastric impactions may be prolonged and is often unrewarding. Intensive fluid therapy (oral and intravenous) along with supportive care, including parentral nutritional support, may result in resolution of the gastric impaction. Detecting and treating gastric impactions early in their course, before the stomach becomes severely distended and the feed mass dries out, is crucial to a successful outcome. CVJ