Mesothelioma is diagnosed using a patient’s history and physical, radiographic studies, and pathologic examination of tissue.
Key components in the patient’s history are exposure to asbestos and complaints relating to fluid build up or a mass, such as pain or shortness of breath. Patients often undergo tests to rule out other conditions, as early symptoms tend to be non-specific.
Radiographic studies include plain films, CT, MRI, or PET, of the chest and abdomen.
Chest x-rays may show effusion, thickening, calcifications, scarring, or a chest mass. CT scans can help guide needle biopsy. MRI can reveal lymph node or diaphragm involvement. PET is now considered the gold standard for staging the disease. These studies are often used in combination for diagnosis, staging, and treatment decisions.
Pathologic examination of the tissues involved confirms a suspected diagnosis. Tissue is removed from the affected site and studied microscopically for evidence of cancer cells.
Mesothelioma is a rare form of cancer caused by exposure to asbestos. It attacks the lining of the lungs (the pleura), the lining of the sac surrounding the heart (the pericardium), or the lining of the abdominal cavity (the peritoneum).
There are three cancer cell types in mesothelioma: epithelioid, sarcomatous, and mixed, which includes both epithelioid and sarcomatous cells. These are abnormal cells which multiply and cause fluid build-up, thickening, or tumors, and therefore impede the normal structure and function of the heart, lungs, or abdominal organs.
Symptoms of pleural mesothelioma may include shortness of breath, pain, or cough, as a result of fluid build up in the pleural space. On auscultation, normal breath sounds are diminished. Peritoneal mesothelioma can present as swelling or distention (increased girth related to ascites), or pain related to a mass. Symptoms of both are often non-specific in the early stages.
The treatment options for mesothelioma are surgery, chemotherapy, radiation or a combination of all three. Surgical options include pleurectomy with decortication and extrapleural pneumonectomy. Pleurectomy with decortication involves dissection and removal of the parietal pleura with decortication of the visceral pleura. Extrapleural pneumonectomy is indicated in early stages of the disease when the mesothelioma is confined to the chest cavity. It involves dissection of the parietal pleura; division of the pulmonary vessels in addition to en bloc resection of the pleura, lung, pericardial sac as well as the diaphragm. For surgical treatment to be an option the patient must have adequate cardiopulmonary function. Chemotherapy currently used in treatment of mesothelioma is Alimta/Cisplatin and is considered the first line treatment in patients who are not surgical candidates.
One of the major risk factors for mesothelioma is asbestos exposure. The disease has a long latency phase and may present 40 years after exposure. The mechanism of action of asbestos causing mesotheliomas is not clearly known but may be related to prolonged exposure of the serous membranes to a foreign body. The fibers may be inhaled or ingested and remain in the body. There are two types of fibers associated with asbestos; Crocidolite, which is the most carcinogenic, and Chrysotile. Tumor growth usually begins in the inferior chest wall. Eventually mesothelioma will grow and encase the chest wall causing lung restriction. Typically mesothelioma does not metastases distantly, but remains confined to the chest cavity.
The use of a combination of testing is needed for proper diagnosis of mesothelioma because it can be easily confused with other carcinomas of the lung as well as other diseases. Chest x-ray is often the first line in diagnostic studies and may show obliteration of the diaphragm and thickening of the pleura, however, it is not specific for mesothelioma. Computed tomography (CT) is more helpful in distinguishing tumor characteristics and the extent of infiltration in to the pleura and will show irregular pleural nodular thickening. Magnetic resonance imaging (MRI) with gadolinium-based contrast material may be useful in defining the extent of penetration into the diaphragm and chest cavity. Thoracoscopic biopsies are necessary to confirm the diagnosis and have 98% specificity for mesothelioma.
Patients with pleural mesothelioma often have a presentation with insidious onset of dyspnea, nonpleuritic chest pain, cough, increased sputum production, weight loss, fevers, sweats and increasing weakness. On physical examination patients may have clubbing of the fingernails, dullness to percussion of the chest and decreased breath sounds of the lungs with auscultation caused by pleural effusion. Pleural effusion caused by mesothelioma will not have a mediastinal shift to the opposite side of the chest, as seen in typical pleural effusions, because of the restriction placed on the chest wall. With palpation of the chest wall there may be a coarse vibration, usually on inspiration, that suggest a pleural friction rub caused by inflammation of the pleural surfaces, the feeling is analogous to the feel of leather rubbing on leather. Patients usually have an occupational history of asbestos exposure, such as construction or ship yards.
Mesothelioma is benign or malignant sarcomas that arise from the mesothelial lining that covers the serous membranes of the pleura, peritoneum and pericardium. The incidence of mesotheliomas occurring in the pleura is highest accounting for 80%. The occurrence for mesotheliomas in the peritoneum is 5%. The rarest occurrence is in the pericardium with only 0.4 % being the primary sight. Mesotheliomas are related to past occupational asbestos exposures. The asbestos exposures may have been a short duration of 1 to 2 years occurring 20 to 25 years in the past with a peak incidence of 35 to 40 years. Mesotheliomas present in the fifth to seventieth decades of life. Males are 3 to 5 times more likely to present with mesotheliomas then are females. There is no racial predilection of disease development. The mortality rate is less than 5% for 5 years.
• The survival rate for malignant pleural mesothelioma without treatment ranges from 4 to 12 months.
• The prognosis is poor even with treatment. Fifty percent of patients are dead within 1 year after diagnosis. The prognosis depends on the stage of the tumor, the histological type, and lymph node status.
• Treatment often includes combination therapy involving surgery with radiation, chemotherapy, or immunotherapy.
• Pleurectomy/decortication is the most common surgery performed and involves removing the lining of the chest. This procedure is usually reserved for early stage disease.
• Alimta (pemetrexed) is a new drug recently approved by the FDA for treatment of malignant pleural mesothelioma. Clinical trials have demonstrated an increase in survival time when used in combination with Cisplatin.
Immountherapy with interferon alpha has lead to a reduction in tumor mass in more than 20% of patients.
• Chest x-ray
-A chest x-ray can reveal a pleural effusion when more than 300 mL of fluid is present in the pleural cavity.
-Other signs of pleural mesothelioma that can be seen on a chest x-ray include pleural calcifications, thickening of the pleural, or an irregular pleural-based mass.
• CT and MRI
-They are used to determine the tumor burden, demonstrate pleural thickening, assess enlargement of lymph nodes, and to identify effusions.
• Tests of tissue and fluid samples
-Thorancetesis is used to obtain pleural fluid, if an effusion is present.
-Thoracoscopy can be used to sample a pleural or pericardial tumor.
-Laproscopy is used to see and obtain a biopsy of a peritoneal tumor.
-Mediastinoscopy allows for biopsy and visualization of the lymph nodes.
• Electron microscopy
-The distinction between malignant mesothelioma and benign inflammatory conditions may be difficult. Electron microscopy can be confirmatory.
• Systemic manifestations may be present with any type of malignant mesothelioma and include weight loss, malaise, anorexia, and fever.
• Types of mesothelioms
-Pleural mesothelioma
-Symptoms include pain in the back or the lower chest, dyspnea, and dry cough. The presence of a large pleural effusion (more than 200-300 mL of pleural fluid) can be detected clinically by the absence of chest wall movement, mediastinal shift to the opposite side, decreased breath sounds, and dullness to percussion over the effusion.
-Peritoneal mesothelioma
-Symptoms include abdominal pain, bowel obstruction, and abdominal distension due to ascites or bowel obstruction.
-Pericardial mesothelioma
-Symptoms may include pain, dyspnea, and cough. A pericardial friction rub may be present. Cardiac tamponade is an ominous sign and is suggested by symptoms of tachycardia, tachypnea, and a narrow pulse pressure.