esophageal NEOPLASIA AND PERIESOPHAGEAL MASSES

Esophageal neoplasia occurs uncommonly in dogs and cats. Malignant tumors of the esophagus include squamous cell carcinoma, osteosarcoma, fibrosarcoma, and undifferentiated carcinoma.

Esophageal neoplasia is discussed in detail in Chapter 11. Spirocerca lupi will be described in this section. Mass lesions arising from the periesophageal tissues may cause esophageal obstruction by com­pressing the walls of the esophagus. This type of obstruction is somewhat more common in cats than in dogs. Anterior mediastinal lymphoma is most common. Other causes include thymic masses, lymphadenopathy, and lung masses. I have observed a cat with a periesophageal stricture and pleural effusion that had an undifferentiated sar­coma (based on cytologic analysis of the effusion).

The endoscopic appearance associated with periesophageal compression includes normal mucosa and collapsed walls. The characteristic sign is an inability to dilate the esophagus with air. It is often also difficult to advance the endoscope through the narrowed esophageal lumen.

Clinical Signs

Esophageal tumors usually occur in older patients. Many dogs and cats with primary esophageal tumors are asymptomatic until quite late in the course of the disease. The diagnosis is often initially made as an inciden­tal finding on survey thoracic radiographs that are made for some other reason.When clinical signs do develop, they primarily include slowly progressive regurgitation and inappetence.

Mediastinal lymphoma occurs most commonly in young cats. Regurgitation occurs when the mass becomes large enough to compress the esophagus. Other potential signs include dyspnea from pleural effusion, a noncompressible cranial thorax, and Horner's syndrome. Diagnosis and treatment are discussed in Chapter 11.

Spirocerca Lupi

S. lupi is a nematode parasite of dogs in the south­ern United States. There is a developmental period of 6 months. The parasite lives in the wall of the esophagus. The parasite lays eggs that pass into the lumen of the esophagus and subsequently pass through the GI tract and out of the body in the feces. Coprophagic beetles ingest eggs, which then hatch and encyst in the beetle. This stage is infec­tive for dogs. Birds and rodents may act as transport hosts. Following ingestion, the encysted larvae are freed and migrate through the wall of the stomach and the aorta to the esophagus, where they mature. Larval migration and worm nodules in the esopha­gus can cause aortic aneurysms, spondylosis in adja­cent vertebral bodies, esophageal granulomas, and esophageal neoplasia. Fibrosarcoma and osteosar­coma of the esophagus are often associated with S. lupi.An interesting feature of the spondylosis is that it forms immediately below vertebral bodies, with no bridging to another vertebral body until the dis­ease is very advanced. Hypertrophic osteopathy has been reported in cases of esophageal fibrosarcoma with and without pulmonary metastasis.

Diagnosis of S. lupi esophageal granulomas may be made by lesion appearance and location. Ova may occasionally be identified in the feces. In one recent report of seven cases, ova were found in the feces of only two of the dogs. Six dogs had signs of esophageal disease, and one dog did not. Four dogs had evidence on thoracic radiographs of a caudodor- sal mediastinal mass. Two of these dogs had spondyli­tis of midthoracic vertebrae.

Disophenol had been the only anthelmintic proven effective against the adult stage of S. lupi. It is not effective against larval stages. Further, it is no longer available. Doramectin (Dectomax, Pfizer Animal Health) has now been shown to be effec­tive in treatment of S. lupi. Treatment before doramectin became available was limited to surgi­cal excision of the esophageal granulomas.

In the study cited here, doramectin was adminis­tered at a dosage of 90 μg∕lb SQ every 2 weeks for three treatments. Endoscopy was then performed at 2, 4, and 6 weeks after treatment. Six weeks after treatment, clinical signs had resolved in six dogs. The esophageal lesions were completely resolved in four of the dogs and reduced in size in the other three dogs. Two dogs with incomplete resolution were subsequently treated with doramectin admin­istered orally at 225 μg∕lb daily for 6 weeks. Esophageal nodules resolved in all dogs, as con­firmed by endoscopy, and there was no recurrence at 3 years. No adverse clinical signs were noted.