Gastric Polyp

A gastric polyp is a protrusion of the gastric mucosa into the lumen of the stomach, typically discovered incidentally during upper gastrointestinal endoscopy or at necropsy. These lesions are generally benign, but some may have malignant potential. Gastric polyps are classified histologically into several types, including hyperplastic (or regenerative) polyps, adenomatous polyps, inflammatory polyps, and fundic gland polyps. In veterinary medicine, hyperplastic polyps are the most common, particularly in dogs, while adenomatous polyps are less frequent but carry a higher risk of malignant transformation. Gastric polyps can be solitary or multiple, sessile or pedunculated, and may cause clinical signs due to mechanical obstruction, ulceration, or bleeding. They are distinct from gastric carcinoma, which is a malignant epithelial neoplasm, and from gastrointestinal stromal tumors (GISTs), which arise from the muscularis propria. The clinical significance of gastric polyps lies in their potential to cause chronic vomiting, hematemesis, and weight loss, and in the need to differentiate them from malignant lesions.

The exact etiology of gastric polyps in dogs and cats is not fully understood, but several factors are implicated. Chronic inflammation of the gastric mucosa, often due to Helicobacter spp. infection, gastritis, or chronic use of non-steroidal anti-inflammatory drugs (NSAIDs), is considered a major predisposing factor. Hyperplastic polyps are thought to arise from excessive mucosal regeneration in response to chronic injury. Adenomatous polyps may develop from dysplastic changes in the gastric epithelium, potentially linked to genetic mutations (e.g., in the APC gene, similar to familial adenomatous polyposis in humans). Inflammatory polyps are associated with chronic inflammatory bowel disease or eosinophilic gastritis. Fundic gland polyps, though rare in animals, may be associated with prolonged proton pump inhibitor (PPI) therapy in humans, but this has not been confirmed in veterinary patients. No specific viral or bacterial agent has been directly implicated as a cause of gastric polyps, but Helicobacter pylori infection is a known risk factor for gastric adenocarcinoma and may also contribute to polyp formation. Genetic predisposition is suspected in certain breeds, such as the Boxer and other brachycephalic breeds, which are prone to gastric tumors. Environmental factors, including dietary carcinogens and exposure to nitrosamines, may also play a role, though evidence is limited.

Gastric polyps are relatively uncommon in dogs and cats compared to other gastric lesions. They are more frequently diagnosed in dogs than in cats. In dogs, the mean age at diagnosis is around 8-10 years, with no strong sex predilection, though some studies suggest a slight male predominance. Certain breeds appear to be overrepresented, including the Boxer, Bulldog, and other brachycephalic breeds, possibly due to their higher incidence of chronic gastritis. In cats, gastric polyps are rare, but when they occur, they are often associated with chronic inflammatory conditions. The prevalence of gastric polyps in the general canine population is estimated to be less than 1% based on endoscopic and necropsy studies. However, in a study of dogs undergoing endoscopy for chronic vomiting, gastric polyps were found in approximately 2-3% of cases. There is no known geographic or seasonal variation. The clinical significance of gastric polyps lies in their potential to cause morbidity and, in the case of adenomatous polyps, progression to adenocarcinoma, although the malignant transformation rate is low.

The pathophysiology of gastric polyps involves a complex interplay of chronic mucosal injury, inflammation, and dysregulated cellular proliferation. In hyperplastic polyps, chronic gastritis leads to mucosal damage and subsequent regenerative hyperplasia of the gastric foveolar epithelium. This results in elongation and branching of the gastric pits, with an increased number of mucus-secreting cells. The polyps are typically well-differentiated and lack significant cellular atypia. In contrast, adenomatous polyps arise from dysplastic changes in the gastric epithelium, characterized by loss of normal cellular maturation, nuclear atypia, and increased mitotic activity. These polyps have malignant potential and can progress to adenocarcinoma over time. Inflammatory polyps are composed of granulation tissue and inflammatory cells, often in response to chronic inflammation or foreign body reactions. Fundic gland polyps, when they occur, are derived from the gastric fundic glands and are usually benign. The mechanical effects of polyps, such as obstruction of the pyloric outflow tract or gastric outlet, can lead to gastric dilation, delayed emptying, and vomiting. Ulceration of the polyp surface can cause gastrointestinal bleeding, leading to anemia and hematemesis. Additionally, large polyps may undergo torsion or infarction, causing acute abdominal pain.

Several factors predispose animals to the development of gastric polyps. Chronic gastritis, particularly due to Helicobacter spp. infection, is a significant risk factor. The use of non-steroidal anti-inflammatory drugs (NSAIDs) can cause gastric mucosal injury and inflammation, promoting polyp formation. Inflammatory bowel disease (IBD) and food allergies can lead to chronic gastric inflammation. Genetic predisposition is suggested by breed predilections, such as in Boxers and other brachycephalic breeds. Age is a risk factor, with older animals being more commonly affected. Concurrent endocrine diseases, such as hypothyroidism or hyperadrenocorticism, may alter gastric mucosal integrity and immune responses. Dietary factors, including high-fat diets or diets containing carcinogens, may contribute. Additionally, chronic stress and environmental factors may exacerbate gastric inflammation. In cats, chronic kidney disease and the associated uremic gastritis may predispose to polyp formation, although this is not well-documented.

Clinical signs of gastric polyps are often nonspecific and may be absent in small polyps. When present, they include chronic intermittent vomiting, which may be postprandial and can contain blood (hematemesis). Regurgitation may occur if the polyp causes esophageal irritation or obstruction. Weight loss and decreased appetite are common, especially with larger polyps or malignant transformation. Melena or hematochezia may be observed if there is significant gastrointestinal bleeding, leading to anemia and lethargy. In cases of pyloric obstruction, signs of gastric outflow obstruction, such as projectile vomiting and abdominal distension, may be seen. Physical examination findings are often unremarkable, but palpation of a cranial abdominal mass may be possible in large polyps. Chronic blood loss can result in pale mucous membranes and signs of weakness. In advanced cases, signs of systemic illness, such as fever and dehydration, may be present.

Differential diagnoses for gastric polyps include gastric adenocarcinoma, lymphoma, gastrointestinal stromal tumors (GISTs), leiomyoma, leiomyosarcoma, inflammatory polyps, and foreign body granulomas. Gastric adenocarcinoma is a malignant epithelial neoplasm that often presents with weight loss, vomiting, and anemia; it is more infiltrative and may cause gastric wall thickening. Lymphoma, particularly in cats, can present as a mass or diffuse infiltration. GISTs arise from the muscularis propria and are typically more vascular and larger. Leiomyomas are benign smooth muscle tumors that may be indistinguishable from polyps on endoscopy. Inflammatory polyps are associated with chronic inflammation and may resolve with treatment of the underlying cause. Foreign body granulomas can mimic polyps but are usually associated with a history of ingestion. Other conditions such as chronic gastritis, gastric ulceration, and gastric dilation-volvulus should also be considered. Definitive diagnosis requires histopathology.

The diagnostic approach to gastric polyps begins with a thorough history and physical examination. If gastric disease is suspected, baseline blood work (CBC, serum biochemistry, urinalysis) and abdominal radiographs are recommended. Radiographs may reveal a soft tissue mass or gastric wall thickening, but are often unremarkable. Abdominal ultrasonography is more sensitive for detecting gastric masses and can assess wall thickness and regional lymph nodes. However, the gold standard for diagnosis is upper gastrointestinal endoscopy, which allows direct visualization of the polyp and biopsy. Endoscopic findings include a sessile or pedunculated mass, which may be erythematous or ulcerated. Multiple biopsies should be taken from the polyp and surrounding mucosa. If endoscopy is not available, surgical exploration and full-thickness biopsy may be necessary. Histopathology is essential to classify the polyp type and assess for malignancy. Advanced imaging such as CT or MRI may be used for staging if malignancy is suspected.

Laboratory findings in gastric polyps are often nonspecific. Complete blood count (CBC) may reveal anemia (regenerative or non-regenerative) due to chronic blood loss, with decreased hematocrit and hemoglobin. Microcytic hypochromic anemia may be seen with iron deficiency. Serum biochemistry may show hypoalbuminemia due to protein-losing enteropathy, particularly if there is significant mucosal inflammation. Electrolyte imbalances, such as hypokalemia and hyponatremia, may occur with chronic vomiting. Liver enzymes may be mildly elevated if there is concurrent hepatic disease. Urinalysis is usually unremarkable. Specific biomarkers such as canine pancreatic lipase immunoreactivity (cPLI) or feline pancreatic lipase immunoreactivity (fPLI) may be normal. Fecal occult blood testing may be positive. In cases of Helicobacter infection, serology or PCR may be positive, but this is not specific for polyps.

Radiography: Abdominal radiographs may show a soft tissue mass in the gastric area, but this is often not visible. In cases of gastric outflow obstruction, gastric dilation may be evident. Ultrasonography: Abdominal ultrasound can reveal a focal mass arising from the gastric wall, with variable echogenicity. The gastric wall may be thickened, and Doppler ultrasound can assess vascularity. Endoscopy: This is the primary imaging modality for gastric polyps. It allows direct visualization of the polyp, assessment of its size, shape, and location, and enables biopsy. Polyps appear as smooth, round, or lobulated masses protruding into the lumen. They may be sessile or pedunculated, and the overlying mucosa may be erythematous, ulcerated, or normal. CT and MRI: These are useful for staging if malignancy is suspected, as they can assess local invasion, lymph node involvement, and metastasis. They are not routinely used for simple polyps.

Cytology: Fine needle aspiration (FNA) of gastric polyps is rarely performed due to the difficulty of targeting the lesion percutaneously. Endoscopic brushing or FNA may be attempted, but cytology is often inconclusive due to the low cellular yield and the presence of inflammatory cells. Histopathology: This is the gold standard for diagnosis. Hyperplastic polyps show elongated, branching gastric pits with an increased number of mucus-secreting cells, but with normal cellular maturation and no significant atypia. Adenomatous polyps exhibit dysplastic changes, including nuclear hyperchromasia, pleomorphism, and increased mitotic activity. Inflammatory polyps are composed of granulation tissue and inflammatory cells. Fundic gland polyps show cystic dilation of the fundic glands. Special stains, such as immunohistochemistry for Ki-67, may be used to assess proliferative activity. If malignancy is suspected, additional stains for cytokeratin and vimentin may help differentiate epithelial from mesenchymal tumors.

Treatment of gastric polyps depends on the type, size, and clinical signs. Small, asymptomatic polyps may be managed conservatively with regular monitoring. However, if the polyp is causing clinical signs, is large, or is suspected to be adenomatous, surgical removal is recommended. Endoscopic polypectomy is the preferred method for pedunculated polyps, using a snare and electrocautery. For sessile polyps, endoscopic mucosal resection (EMR) may be attempted, but surgical resection may be necessary. In cases of multiple polyps or diffuse polyposis, partial gastrectomy may be required. Medical management includes treatment of underlying gastritis with proton pump inhibitors (e.g., omeprazole at 0.7-1.0 mg/kg PO q12h) or H2 blockers (e.g., famotidine at 0.5-1.0 mg/kg PO q12h). If Helicobacter infection is confirmed, a combination of amoxicillin (20 mg/kg PO q12h), clarithromycin (7.5 mg/kg PO q12h), and omeprazole (1 mg/kg PO q12h) for 14 days may be used. Supportive care includes antiemetics (e.g., maropitant at 1 mg/kg SC q24h), fluid therapy, and nutritional support. In cases of gastrointestinal bleeding, blood transfusion may be necessary. Follow-up endoscopy is recommended to monitor for recurrence.

The prognosis for gastric polyps is generally good, especially for hyperplastic and inflammatory polyps, which are benign and have a low risk of malignant transformation. Surgical or endoscopic removal is often curative. However, adenomatous polyps have a higher risk of progressing to adenocarcinoma, and the prognosis depends on the degree of dysplasia and the completeness of excision. If malignant transformation has occurred, the prognosis is guarded, with a median survival time of several months to a year, depending on the stage. Recurrence is possible, especially if the underlying inflammatory condition is not managed. Regular monitoring with endoscopy is recommended for animals with a history of gastric polyps.

After removal of a gastric polyp, follow-up endoscopy is recommended within 3-6 months to assess for recurrence and to evaluate the healing of the biopsy site. If the polyp was benign and completely excised, annual monitoring may be sufficient. For adenomatous polyps, more frequent monitoring (every 3-6 months) is advised. Serial blood work, including CBC and serum biochemistry, should be performed to monitor for anemia and electrolyte imbalances. If the animal is on long-term acid suppressants, periodic monitoring of renal function and electrolytes is recommended. Management of underlying conditions, such as chronic gastritis or Helicobacter infection, is essential to prevent recurrence. Owners should be educated on the signs of gastric disease, such as vomiting, and to seek veterinary attention promptly.

Pearls: 1. Gastric polyps are often incidental findings; however, if clinical signs are present, they should be biopsied to rule out malignancy. 2. Endoscopic polypectomy is a safe and effective treatment for pedunculated polyps. 3. Always biopsy the surrounding mucosa to assess for concurrent gastritis or dysplasia. 4. In dogs with chronic vomiting, consider gastric polyps as a differential, especially in older brachycephalic breeds. 5. If a polyp is large or ulcerated, consider the possibility of bleeding and anemia. Pitfalls: 1. Do not assume a polyp is benign without histopathology; adenomatous polyps can be malignant. 2. Avoid using NSAIDs in animals with gastric polyps, as they can exacerbate inflammation and bleeding. 3. Do not overlook the possibility of multiple polyps; perform a thorough endoscopic examination. 4. In cats, gastric polyps are rare, but if present, they may be associated with inflammatory bowel disease; investigate accordingly. 5. Failure to treat underlying Helicobacter infection may lead to recurrence.

For gastric polyps, the primary treatment is surgical or endoscopic removal. Medical therapy is adjunctive and aimed at managing gastritis and reducing gastric acid secretion. Proton pump inhibitors: Omeprazole at 0.7-1.0 mg/kg PO q12h (dogs) and 0.7-1.0 mg/kg PO q12h (cats) for 2-4 weeks. H2 receptor antagonists: Famotidine at 0.5-1.0 mg/kg PO q12h (dogs and cats) for 2-4 weeks. Antiemetics: Maropitant at 1 mg/kg SC q24h (dogs) or 1 mg/kg PO q24h (dogs) for up to 5 days; for cats, 1 mg/kg SC q24h. Sucralfate at 0.5-1 g PO q8h (dogs) and 0.25-0.5 g PO q8h (cats) can be used as a cytoprotectant. If Helicobacter infection is confirmed, a triple therapy protocol: Amoxicillin 20 mg/kg PO q12h, Clarithromycin 7.5 mg/kg PO q12h, and Omeprazole 1 mg/kg PO q12h for 14 days. For gastrointestinal bleeding, consider blood transfusion if anemia is severe. Always adjust dosages in patients with renal or hepatic impairment. Avoid concurrent use of NSAIDs and corticosteroids.

There is limited evidence-based literature specifically on gastric polyps in veterinary medicine. Most information is extrapolated from human medicine and small case series. A retrospective study by Gualtieri et al. (2000) described the endoscopic and histopathologic features of gastric polyps in dogs, finding that hyperplastic polyps were the most common and that they were often associated with chronic gastritis. Another study by Willard et al. (2005) reported that gastric polyps in dogs were frequently incidental findings and that surgical removal was curative. In cats, gastric polyps are rare, but a case report by Trepanier et al. (2003) described a feline gastric polyp associated with inflammatory bowel disease. Consensus guidelines from the ACVIM on chronic gastritis recommend biopsy of any gastric mass to rule out neoplasia. The World Small Animal Veterinary Association (WSAVA) guidelines for gastrointestinal endoscopy emphasize the importance of histopathology for diagnosis. Overall, the evidence suggests that gastric polyps are benign in most cases, but adenomatous polyps carry a risk of malignancy, and complete excision is recommended.