DISCUSSION

Esophageal tumors account for less than 0.5% of all canine neoplasms.¹ Most esophageal tumors occur in older animals, and they are often malignant. The most commonly reported primary esophageal tumors are sarcomas (osteosarcoma and fibrosarcoma), squamous cell carcinoma, and leiomyosarcoma; benign tumors such as leiomyoma and plasmacytoma occur less often.² Metastatic tumors are three times more common than primary esophageal tumors and occur through local invasion from the stomach, thymus, thyroid, and heart base as well as from mammary adenocarcinoma and lymphoma.¹ In dogs, the most common primary esophageal tumors are osteosarcoma and fibrosarcoma, particularly in areas where Spirocerca lupi is endemic (Africa, Asia, southeastern United States) because neoplastic transformation of S. lupi granulomas frequently occurs.³ In cats, the most common primary esophageal tumor is squamous cell carcinoma.⁴

Leiomyomas are benign tumors of smooth muscle origin arising in the gastrointestinal tract. The well-defined, round-to-ovoid masses are thinly encapsulated and expansile, usually with no ulceration of the overlying mucosa.⁵ Most (80%) arise intramurally from the muscularis propria (deep muscular layer), with a smaller percentage being pedunculated and arising from the muscularis mucosae. Esophageal leiomyomas are usually individual, slow-growing tumors, although multiple tumors can occur. In dogs, leiomyomas are most commonly found in the stomach at the gastroesophageal junction, and incidence increases with age.⁵ In people, leiomyomas occur most frequently in the esophagus and account for two-thirds of all benign esophageal tumors.⁶

Clinical signs

Clinical signs of esophageal tumors are most commonly due to luminal obstruction or motility dysfunction causing regurgitation and dysphagia. Other signs include weight loss, pain, and aspiration pneumonia. In some cases, respiratory signs may be the only signs.^1,9 The history of dyspnea, coughing, and panting seen in this case is speculated to be due to minor episodes of aspiration secondary to dysphagia.

Esophageal tumors smaller than 2 cm seldom produce clinical signs.¹⁰ Leiomyomas at the gastroesophageal junction can be an incidental finding in asymptomatic patients at necropsy.⁵ However, in one dog, an esophageal leiomyoma just proximal to the lower esophageal sphincter was associated with megaesophagus and hypomotility.⁹ Large intra-abdominal leiomyomas and leiomyosarcomas have been reported to cause hypoglycemia in dogs as a paraneoplastic syndrome, likely because of the production of insulinlike growth factors.¹¹ In people with esophageal leiomyomas, 15% to 50% of patients are asymptomatic, with no direct correlation between tumor size and the severity of symptoms.⁶

Diagnosis

Thoracic radiographs may reveal a homogeneous mass in the region of the esophagus, with gas retention and dilatation proximal to the lesion. The mass may also appear calcified.^1,6,9 A barium esophagogram typically reveals a rounded or lobulated, smoothly elevated filling defect. CT can identify the tumor's size and location as well as invasiveness. Esophagoscopy reveals a submucosal tumor over which the mucosa is usually freely movable. Lumen narrowing is common, while stenosis and obstruction are rare. In people, endoscopic ultrasonography is also commonly used for diagnosis.

Definitive diagnosis is provided by histologic examination, but endoscopic biopsies are contraindicated with leiomyomas, as they increase the risk of complications and mucosal perforation during surgery.⁶ Endoscopic fine-needle aspiration is effective for obtaining a firm diagnosis and does not affect surgical outcome.¹² Leiomyoma can be presumptively diagnosed based on endoscopic examination and CT results that indicate a well-defined, round-to-ovoid encapsulated mass, with no ulceration of the overlying mucosa or evidence of local invasion.