Malignant Mesothelioma

• Most common primary neoplasm of pleura
• Prevalence
  • 2,000-3,000 cases/year in US
    
    
• Etiology
  
  
  • Asbestos exposure
  • Zeolite (non-asbestos mineral fiber)
  • Chronic inflammation (TB, empyema)
  • Radiation
    
    
• Peak age
  
  
  • 50-70 years
  • M:F = 4-6:1
    
    
• Histology
  
  
  • Epithelioid (60%)
  • Sarcomatoid (15%)
  • Biphasic (25%)
  • Intracellular asbestos fibers in 25%
• Carcinogenic potential: crocidolite > amosite > chrysotile > actinolite, anthophyllite, tremolite
• Occupational exposure of asbestos found in only 40-80% of all cases
• 5-10% of asbestos workers will develop mesothelioma (risk factor of 30X compared with general population)
• No relation to duration/degree of exposure to asbestos or smoking history
• Latency period
  • 20-45 years
    • Earlier than asbestosis
    • Later than asbestos-related lung cancer
      
      
• Pathology
  
  
  • Multiple tumor masses involving predominantly the parietal pleura and to a lesser degree the visceral pleura
  • Progresses to thick sheet-like / confluent masses resulting in lung encasement
• Associated with
  • Peritoneal mesothelioma
  • Hypertrophic osteoarthropathy (10%)
• Staging (Boutin modification of Butchart staging)
  • IA confined to ipsilateral parietal / diaphragmatic pleura
  • IB+ visceral pleura, lung , pericardium
  • II invasion of chest wall / mediastinum (esophagus, heart, contralateral pleura) or metastases to thoracic lymph nodes
  • III penetration of diaphragm with peritoneal involvement or metastases to extrathoracic lymph nodes
  • IV distant hematogenous metastases
• Stage at presentation
  • II in 50%
  • III in 28%
  • I in 18%
  • IV in 4%
    
    
• Clinical signs and symptoms
  
  
  • Non-pleuritic (56%) / pleuritic chest pain (6%)
  • Dyspnea (53%)
  • Fever + chills + sweats (30%)
  • Weakness, fatigue, malaise (30%)
  • Cough (24%)
  • Weight loss (22%)
  • Anorexia (10%)
  • Expectoration of asbestos bodies (= fusiform segmented rod-like structures = iron-protein deposition on asbestos fibers [a subset of ferruginous bodies])
    
    
• Spread
  
  
  • Contiguous: chest wall, mediastinum, contralateral chest, pericardium, diaphragm, peritoneal cavity; lymphatics, blood
  • Lymphatic
    • Hilar + mediastinal (40%)
    • Celiac (8%)
    • Axillary + supraclavicular (1%)
    • Cervical nodes
  • Hematogenous: lung, liver, kidney, adrenal gland
    
    
• Imaging findings
  
  
  • Extensive irregular lobulated bulky pleural-based masses typically >5 cm / pleural thickening (60%)
  • Exudative / hemorrhagic unilateral pleural effusion (30-60-80%) without mediastinal shift; effusion contains hyaluronic acid in 80-100%; bilateral effusions (in 10%)
  • Distinct pleural mass without effusion (<25%)
  • Associated with pleural plaques in 50% = pathologic HALLMARK of asbestos exposure
  • Pleural calcifications (20%)
  • Circumferential encasement = involvement of all pleural surfaces (mediastinum, pericardium, fissures) as late manifestation

Thick rind of irregular, nodular, malignant mesothelioma encases the left lung.
There is a large pleural effusion present.

• Extension into interlobar fissures (40-86%)
• Rib destruction in 20% (in advanced disease)
• Ascites (peritoneum involved in 35%)

• CT
  • Pleural thickening (92%)
  • Thickening of interlobar fissure (86%)
  • Pleural effusion (74%)
  • Contraction of affected hemithorax (42%):
  • Ipsilateral mediastinal shift
  • Narrowed intercostal spaces
  • Elevation of ipsilateral hemidiaphragm
  • Calcified pleural plaques (20%)
• MR (best modality to determine resectability)
  • Minimally hyperintense relative to muscle on T1WI
  • Moderately hyperintense relative to muscle on T2WI
• Metastases to:
  • Ipsilateral lung (60%)
  • Hilar and mediastinal nodes
  • Contralateral lung and pleura (rare)
  • Extension through chest wall and diaphragm
    
    
• Prognosis
  
  
  • 10% of occupationally exposed individuals die of mesothelioma (in 50% pleural + in 50% peritoneal mesothelioma)
  • Mean survival time of 5-11 months
    
    
• DDx
  
  
  • Pleural fibrosis from infection (TB, fungal, actinomycosis)
  • Fibrothorax
  • Empyema
  • Metastatic adenocarcinoma
    
    
• Diagnosis
  
  
  • Video-assisted thoracoscopic surgery (postprocedural radiation therapy of all entry ports for tumor seeding of needle track [21%])