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Malignant Mesothelioma

 

  • Most common primary neoplasm of pleura
  • Prevalence
    • 2,000-3,000 cases/year in US
  • Etiology
    • Asbestos exposure
    • Zeolite (nonasbestos 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 sheetlike / 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
    • Nonpleuritic (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 rodlike structures = iron-protein deposition on asbestos fibers)
  • 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
    • 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%)

Circumferentially thickened rind of nodular pleura with large effusion

  • 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%])

 

 

Dahnert 4th edition

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