INTRODUCTION

Tumours in the chest are common and can be divided according to anatomical location. This abstract will review tumours of the chest wall and intrathoracic organs. The intrathoracic organs of interest are the lungs, the heart and the thymus.

Thoracic wall tumours

The most common tumours of the thoracic wall are the tumours arising from the rib cage. Osteosarcoma and chondrosarcoma are frequently described, although tumours from other tissue types can cause similar signs. Of these, fibrosarcoma and mast cell tumours should be included in the differential diagnosis list.

History, clinical signs, and differential diagnosis

Chest wall tumours are often presented as an acute or chronic visible swelling at the affected site. The owner often backdates to a minor traumatic incident and pain can be elicited upon palpation.

Diagnosis

The presumptive diagnosis is easily obtained by fine needle aspiration biopsy and regional radiography. Radiographic changes of the bony chest wall may include a mixed pattern of osteolysis and bony proliferation and either change can predominate. The definite diagnosis is obtained by bone biopsy and histologic examination. The biopsy can be performed using a Jamshidi biopsy needle or Michele bone trephine.

Additional diagnostics may include Scintigraphy, CT or MRI. Scintigraphy will not differentiate benign (non-tumorous) from malignant lesions, and should be followed by radiography of regions with increased uptake. CT-and MRI-scans can be used to estimate the extent of bony and surrounding soft tissue involvement and is an essential tool to estimate the possibility for complete surgical excision.

Prognosis

The prognosis of rib osteosarcoma is described as poorer compared to other types of tumours or the same type in a different location. Median survival times of 3-6 months after surgical excision of OS and 12 months after CSA have been noted. Most likely, this poor outcome is caused by difficulties in obtaining a complete excision or by early metastasis. Some authors suggest bone biopsy before surgical excision of the tumour because surgery is not advised if OS is diagnosed.

Surgery

Tumours of the chest wall should be excised with 2-3 cm margins. This leads often to an en bloc resection of the thoracic wall and one or two normal ribs. Reconstruction of the thoracic wall is necessary after en bloc resection. Large portions of the chest wall can be removed as long as an airtight cover can be reconstructed. Materials that can be used to reconstruct the chest wall include polypropylene mesh, SIS, diaphragmatic advancement flaps or muscle rotation flaps. The use of allografts, surgical stents and/or plastic plates is rarely necessary. A thoracostomy tube is used to evacuated air and fluid from the chest for 24 hours postoperatively.

Technique

The skin covering the tumour is incised and retracted. If possible, muscles that cover the tumour and that are not invaded (determined by CT/MRI imaging) are spared for later closure methods. An entrance to the chest is obtained through a non-affected rib space and the tumour extension is checked by digital palpation or thoracoscopic techniques. The incision is lengthened to remove the tumour with 2-3 cm margins proximally and distally.

An identical procedure is performed in the rib space on the opposite site of the tumour. The ribs are cut proximal and distal to the chest tumour using a rib cutter. The arteries and veins running on the caudal side of the rib are coagulated or sutured with 3-0 absorbable suture material. After adhesions to the tumour are dissected, the tumour is removed and the thoracic cavity is thoroughly inspected for abnormalities. Closure of the chest wall is performed after installing a closed suction chest tube. Foreign materials or muscle can be used to close the defect. An airtight seal is obtained using muscle layers or omentum. The subcutis and skin are closed routinely.

INTRATHORACIC TUMOURS

Pathophysiology

Respiratory oncologic emergencies are caused by acute respiratory distress associated with tumours near or in the respiratory tract. The four most common respiratory emergencies are airway obstruction, haemorrhage, malignant pleural effusion, and superior vena cava syndrome.

Tumour-induced airway obstruction can be caused by intraluminal masses or extraluminal compression. Intraluminal tumours can be located in the larynx, trachea, or main stem bronchi. Various types of tumours have been reported, but the incidence is relatively low. Compressive lesions are often associated with the thyroid (adenocarcinoma), oesophagus (squamous cell carcinoma), lymph nodes (submandibular, retropharyngeal, mediastinal, or hilar), thymus (thymoma, malignant lymphoma), and other mediastinal structures.

Pleural effusion is caused by mediastinal, pleural, or pulmonary tumours that obstruct lymphatic drainage or cause inflammation, hypoalbuminemia, or haemorrhage. Malignant or tumour-induced pleural effusion can be treated effectively by closed-tube thoracostomy and rarely needs immediate surgical intervention.

Superior vena cava syndrome (SVCS) is a clinical expression for obstruction of venous return from head, neck, and fore limbs caused by a process compressing the cranial vena cava. SVCS has been described in the dog, but is extremely rare. Theoretically, SVCS can be caused by extraluminal compression or by tumor ingrowth into the vena cava.

Pulmonary tumours

Pulmonary tumours are relatively common in de dog and rare in the cat. Except for metastatic disease, pulmonary tumours are often treatable by surgery.

History, clinical signs, and differential diagnosis

Respiratory distress and coughing can be clinical signs of pulmonary tumours but often the disease is found on routine radiography in an asymptomatic animal. The most common signs of tumour-induced airway obstruction are progressive dyspnoea, stridor, coughing, and exercise intolerance. Most of these signs are chronic but peracute respiratory dyspnoea can develop because of hyperthermia, oedema and haemorrhage related to the tumour, accumulation of secretions and debris, or laryngeal spasm.

Primary or metastatic lung tumours are reported to cause peracute pneumothorax, haemoptysis, and haemothorax, although the incidence of these complications is low.

Clinical signs caused by pulmonary neoplasia include coughing, dyspnoea, lethargy, weight loss, tachypnoea, haemoptysis, and exercise intolerance.

Diagnosis

Thoracic radiographs and cytologic examination of percutaneous fine needle aspirates are the most valuable diagnostic methods. Further useful diagnostic procedures are laryngeal and tracheal palpation, endoscopy, radiology, and ultrasonography. Early diagnosis can be obtained by endoscopic-guided biopsy.

The additional diagnostic testing (transtracheal lavage, ultrasonography, or bronchoscopy) are often not necessary for solitary lung lesions because in most cases surgical excision is the therapy of choice. In contrast, additional diagnostic testing can be very useful for metastatic disease or pleural effusions. Malignant pleural effusion may cause peracute clinical signs including tachypnoea, dyspnoea, decreased exercise intolerance, abdominal breathing, and cyanosis. Decreased respiratory and cardiac sounds ventrally, in combination with dullness on percussion, are pathognomonic physical findings. Definite diagnosis is made by thoracic radiography and thoracocentesis.

Progressive dyspnoea and swelling of the face, neck, and forelimbs caused by oedema, are the most common signs of SVCS. The onset is often insidious but peracute dyspnoea can be seen as the disease progresses. Radiographs, ultrasonography, and CT-scans of the cranial thorax often allow the tumour to be localized. Diagnosis of tumour type may be obtained using fine needle aspiration or cutting biopsy needle.

Surgical therapy and aftercare

Initial therapy for tumour-induced respiratory emergencies is identical to that for other respiratory distress syndromes and may include supplemental oxygen therapy, tracheostomy, and thoracostomy tube placement. Tumour-induced upper airway obstruction is treated by tracheostomy or tumor removal. To remove tracheal tumours an end-to-end tracheal anastomosis is often necessary. Four rings (12%) of the trachea can be resected easily, although in a few cases successful resection of 25 to 50% of the trachea has been reported. The incidence of tracheal stenosis and dehiscence increases after extensive tracheal resection because of increased longitudinal tension. Chemotherapy and radiation therapy, have been described, and of these, radiation seems to be most successful, especially for malignant lymphoma of the larynx and trachea.

Immediate surgical intervention is seldom necessary in dogs with pulmonary neoplasms. Pneumothorax and pleural effusions are commonly treated successfully with a thoracostomy tubes. Two indications for immediate surgical exploration are active haemorrhage, and a non-productive thoracostomy tube in the presence of serious pneumothorax or pleural effusion. Exploratory thoracotomy is performed via an intercostal incision or median sternotomy. Isolated pulmonary masses are best treated by removal of the affected lung lobe through an intercostal thoracotomy. The use of thoracoabdominal staplers has simplified the procedure and decreased morbidity. Regional lymph nodes are biopsied if enlarged. The prognosis is most favourable in dogs with small tumours and no lymph node involvement. Over 50% of these patients survive at least 1 year after surgery.

There is no proven effective therapy for canine or feline SVCS. Surgical excision of discrete mediastinal, pulmonary, or cardiac masses may eliminate clinical signs. Radiation therapy to reduce the tumour mass appears to be the therapy of choice in man and may be of benefit in animals.

CARDIAC TUMOURS AND NEOPLASTIC CARDIAC TAMPONADE

Pathophysiology

Pericardial effusion caused by neoplasia of the heart or pericardium may result in cardiac tamponade, a potentially life-threatening situation. Tamponade is the uncontrolled increase in intrapericardiac pressure which causes decreased cardiac filling and output. This results in signs of right heart failure because the thinner right ventricle is more susceptible to external pressure. The severity of tamponade depends on the rate of pericardial fluid formation, the volume accumulated, and the ability of the pericardium to stretch. The pericardium can contain large volumes, if the effusion develops gradually, but in acute cases small volumes cause severe clinical signs.

Neoplasia, primary or metastatic, were the most common cause of pericardial effusion in a study of 42 dogs. Primary cardiac tumours are rare and include hemangiosarcoma, heart base tumors, mesothelioma, and sarcoma. Tumours reported to metastasize to the heart or pericardium are hemangiosarcoma, lymphoma, melanoma, and mammary adenocarcinoma. Malignant pericardial effusion is uncommon in cats and is most often caused by lymphoma.

Clinical presentation and diagnosis

Clinical signs associated with acute pericardial effusion and tamponade include lethargy, dyspnoea, anorexia, collapse, abdominal distension, sudden death, exercise intolerance, and coughing. Most effusions develop gradually and cause signs of chronic cardiac compression: weight loss, muffled heart sounds, jugular pulse, ascites, dyspnoea, tachycardia, splenomegaly, and hepatomegaly. Thoracic radiographs, electrocardiography, and ultrasonography can confirm the diagnosis. Pneumopericardiography can be used to detect intrapericardiac masses, alternatively, ultrasonography is often used to detect masses and to guide pericardiocentesis. Pericardiocentesis under ultrasonographic and electrocardiographic guidance can be performed for both diagnostic and therapeutic purposes. An over-the-needle catheter is inserted in the right fourth to sixth intercostal space near the costochondral junction. The right side is preferred to prevent laceration of the coronary artery. After the pericardium is punctured, the catheter is advanced, the needle is removed, and all fluid is evacuated. The pericardial fluid should be submitted for biochemical and cytologic examination. Tumour cells are rarely found during cytologic examination of malignant effusions or, in the case of mesothelioma, are difficult to differentiate from reactive mesothelial cells.

Surgical therapy and aftercare

Therapy of patients with pericardial effusions is directed at quickly reducing intrapericardial pressure by centesis or surgical drainage. Therapeutic pericardiocentesis is indicated in dogs with cardiac tamponade, but is often of short beneficial effect. Immediate surgical intervention is indicated in active intrapericardial haemorrhage, if pericardial distension cannot be relieved, or if clinical signs caused by intrapericardiac masses are severe. The main objective of surgery is to remove the tumour causing the effusion, but palliative pericardiectomy is indicated in selected cases. The surgical approach and procedure depends on tumour localization and tumour type and includes lateral thoracotomy or median sternotomy. Heart base tumours are slow growing and often detected in a late stage of disease, so surgical resection is seldom possible. Pericardiectomy, as a palliative procedure, is a good alternative to euthanasia or repeated pericardiocentesis for these dogs and has allowed comfortable survival up to four years. Hemangiosarcoma is commonly located on the right auricle and can be surgically excised if small. The use of a cardiovascular stapling device allows rapid and save excision, however this therapy is often palliative because of concurrent metastases to the pericardium, lungs, or other distant sites. The prognosis for dogs with cardiac hemangiosarcoma is poor and comparable to involvement of other sites. The median survival of 15 dogs treated with vincristine, doxorubicin, and cyclophosphamide for hemangiosarcoma was 172 days, compared to 60 days in dogs not treated with chemotherapy.

PLEURAL AND MEDIASTINAL TUMOURS

The most common tutor types are the thymoma and the mesothelioma. Thymomas occur in dogs and cats, but are relatively uncommon. An important differential diagnosis is lymphoma. Mesothelioma are rare tumours and can occur anywhere in the chest cavity but mostly affect the complete pleural space.

History, clinical signs, and differential diagnosis

Respiratory distress, regurgitation and oedema of the head and neck area have been described as clinical signs for thymoma, however, the diagnosis is also often made by routine thoracic radiographs. Regurgitation can be caused by a megaesophagus as a part of the myasthenia gravis syndrome. Laboured breathing caused by pleural effusion is the most common sign for mesothelioma

Diagnosis

A cranially located mediastinal mass is observed on thoracic radiographs and the diagnosis can be confirmed by an ultrasound guided fine needle aspirate or histologic biopsy. The diagnosis mesothelioma is confirmed by thoracic radiographs and thoracocentesis. Malignant mesothelial cells are often difficult to differentiate from reactive cells, however. Histologic examination of a biopsy specimen obtained by thoracoscopy or thoracotomy will allow a solid diagnosis.

Prognosis

Noninvasive thymomas can be removed and the prognosis following surgery is good to excellent. Invasive thymomas are rarely cured because of the close approximation of the tumor to vital structures. The prognosis for mesothelioma is poor; no successful therapies have been described.

Surgery

Surgical resection of a thymoma is performed through a cranial sternotomy. The success of surgery mainly depends on the ability to remove the tumor in toto.

References

1.  Orton EC, McCracken T.O. Small Animal Thoracic surgery. Williams and Wilkins 1995.

2.  Kirpensteijn J, van Zuilen C.D. Oncologic surgical emergencies. Vet Clin North Am Small Anim Pract 25;1:207-223