Oesophageal Neoplasia

Introduction

Oesophageal neoplasia is very rare, accounting for less than 0.5% of all neoplasia in dogs. It has a higher incidence in the areas where Spirocerca lupi, a helminth parasite, is endemic in Africa and the south-eastern USA. The most commonly reported forms of neoplasm are:

• Squamous cell carcinoma - usually apparent as an annualar thickening in the middle third of the oesophagus, anterior to the heart base.
• Leiomyosarcoma
• Fibrosarcoma
• Osteosarcoma
• Plasmacytoma
• Local invasion of paraoesophageal tumours is much more common than primary oesophageal neoplasia. The most common metastatic tumours are thyroid carcinomas.
• Benign leiomyomas may occur in the caudal oesophagus and gastric cardia.
• Fibrosarcomas and osteosarcomas are the most common tumours caused by Spirocerca lupi, probably due to the production of a carcinogen by the parasite.

Signalment

Most affected animals are middle-aged or older and there is no breed or sex predilection.

Diagnosis

Clinical Signs

Signs are indicative of partial or complete upper gastro-intestinal obstruction:

• Regurgitation with hypersalivation.
• Difficulty in swallowing (dysphagia) and pain on swallowing (odynophagia). The animal will often appear to stretch its neck and make repeated efforts to swallow.
• Malnutrition due to chronic regurgitation and anorexia, resulting on poor body condition.
• As with any cause of chronic regurgitation, animals may develop aspiration pneumonia with signs of coughing, tachypnoea, dyspnoea and pyrexia.
• Hypertrophic osteopathy (Marie's disease) as a paraneoplastic syndrome, particulary in those animals with sarcomas with caused by Spirocerca lupi infection.

Diagnostic Imaging

Radiography

Plain radiographs of the chest may show a mass of soft tissue opacity associated with the oesophagus, although apparent masses in the caudal oesopahagus could also represent hiatal hernias. Some tumours (such as osteosarcomas) may contain areas of mineralisation. There may be intra-luminal gas retention or an oesopageal stricture with cranial dilation. It should be noted that there are numerous other causes of oesophageal strictures, including peri-oesophageal (thoracic) neoplasia and inflammatory lesions like abscesses and granulomata.

Barium contrast studies may be used to define mucosal irregularities and strictures whereas dynamic lesions, such as swallowing defects and regurgitation, can be assessed by fluoroscopy.

It may difficult to image the mass by ultrasonography but this technique may be useful if the mass lies in the cranial mediastinum or close to the diaphragm.

Endoscopy can allow direct visualisation of the mass if it extends into the oesophageal mucosa and lumen. Grab biopsies can also be taken via the endoscope.

Advanced Imaging Techniques

Computed tomography (CT) and Magnetic resonance imaging (MRI) may be useful in defining the full extent of the lesion and for determining its exact relationship with the oesophagus.

Biopsy

If the mass lies in the cranial mediastinum, samples could be obtaind by ultrasound-guided fine needle aspiration (as for a thymoma or thymic lymphoma). Otherwise, excisional biopsies could be obtained by thoracoscopy.

Faecal Analysis

Ova of Spirocerca lupi may be found in the faeces of affected animals.

Treatment

Surgical Management

Due to the advanced development of many oesophageal neoplasms at the time of diagnosis, complete surgical excision is often problematic. The thoracic oesophagus may be approached by lateral thoracotomy on either side (retracting the brachiocephalic trunk if approaching from the left or ligating the azygos vein if from the right) or via a median sternotomy. The affected portion of the oesophagus is isolated with loops of moist umbilical tape and moist laparotomy swabs are used to pack the oesopahgus off from the thorax. The tumour is excised, together with the largest possible margin of normal tissue and an anastomosis is then created between the two ends of the incision.

Only 3-5 cm of the length of the oesophagus can be resected without risking dehiscence of the anastomosis and it is advisable to restrain the patient in a headcollar and side-reins after the procedure to prevent this site from coming under tension. The oesophagus is especially prone to dehiscence because it is under constant tension (exacerbated by movement) and because it lacks a serosa which is responsible for the formation of an initial fibrin seal during healing of the rest of the gastro-intestinal tract. To support a large resection, intercostal muscle flaps, omentum or synthetic meshes can be wrapped around an anastomotic site. Tension on the oesophagus can also be released by sectioning the phrenico-oesophageal membrane (which attaches it to the diaphragm) or by making a circumferential incision through the outer longitudinal muscle layer. Dehiscence of a surgical wound is one cause of oesophageal rupture. Bougeinage may be used to prevent the formation of strictures at the surgical site. Gastrostomy tubes can be used for short-term palliation of cases with extensive tumours that have obliterated the oesophageal lumen.

One study of 6 dogs that underwent partial oesophagectomy for treatment of S. lupi-related oeophageal sarcomas reported a median survival of 267 days with adjunctive doxorubicin therapy. Another study of 4 dogs with oesophageal leiomyosarcoma reported potential long term resolution of clinical signs following surgical resection (despite incomplete margins) if the tumour was of a low histological grade (all those in the study were of grade 1) .

Chemotherapy

This approach has rarely been reported except as an adjunctive therapy to the surgical removal of S. lupi-associated masses, where doxorubicin was used post-operatively .

Radiotherpy

There is little opportunity to use this technique for oesophageal neoplasia as the surrounding organs (the heart and lungs) have a poor tolerance to radiation. Oesophagitis and oesopageal strictures have also been reported after thoracic radiotherapy.

Prognosis

This is often poor as the disease is usually in its advanced stages at the time of diagnosis, leaving few options for surgical management. In addition, the metastatic rate of oesophageal tumours is high with local invasion and spread to draining lymph nodes (cervical and prescapular nodes from the cervical oesophagus and mediastinal nodes from the thoracic oesophagus) and to distant organs.

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References

• Morris J, Dobson J (2001) Gastrointestinal Tract, in Small Animal Oncology,' Blackwell Science, pp 125-127
• Liptak J. M, Withrow S.J, (2007), Cancer of the Gastrointestinal Tract, in Withrow and MacEwen's Small Animal Clinical Oncology, fourth edition, Eds Withrow S.J, Vail D.M, Missouri, Saunders Elsevier, pp 477-478

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