Mesothelioma

Todd M. Blodgett, MD

Janet Durick, MD

Sanjay Paidisetty, BS

Key Facts

Imaging Findings

Pleural effusion &/or pleural thickening
80% of cases have primary arising from mesothelial surfaces of pleura
- Also seen in peritoneum, pericardium, and tunica vaginalis
Distant metastases historically uncommon due to poor prognosis and rapid demise of patients
75% of pleural mesotheliomas are diffuse (usually malignant)
Nodular, irregular, unilateral pleural thickening
CT findings in mesothelioma by frequency
- Pleural thickening
- Thickening of interlobular fissures
- Pleural effusion
- Pleural calcification
Features helpful in distinguishing malignant from benign pleural disease include
- Circumferential pleural thickening
- Nodular pleural thickening
- Mesothelioma generally FDG avid
FDG PET accurate for prediction of response with serial changes in tumor tracer uptake following one cycle of chemotherapy

Top Differential Diagnoses

Chronic Organized Empyema
Metastatic Tumor to Pleura, Especially Adenocarcinoma
Infection Processes (e.g., Actinomycosis, Tuberculosis, Nocardiosis)
Asbestos-related Pleural Disease

Graphic shows nodular thickening of the right pleura

, representing mesothelioma.

Coronal PET shows increased FDG activity

in theright pleura in a patient with mesothelioma.

TERMINOLOGY

Abbreviations and Synonyms

Malignant mesothelioma (MM)
Peritoneal mesothelioma (PM)
Benign variant: Asbestos-related benign pleural disease

Definitions

Primary neoplasm arising from mesothelial cells that line body cavities

IMAGING FINDINGS

General Features

Best diagnostic clue
- Chest: Pleural effusion, thickening, calcification
- Abdomen: Omental caking or peritoneal masses
Location
- 60-80% of cases have primary arising from mesothelial surfaces of pleura
  - Also seen in peritoneum, pericardium, and tunica vaginalis
- Compared with other intrathoracic malignancies, lymphatic pattern of spread of mesothelioma is unpredictable
- Distant metastases historically uncommon due to poor prognosis and rapid demise of patients
  - Recent reports more common
  - Reported in brain, lung, bone, adrenals, peritoneum, abdominal lymph nodes, and abdominal wall
Size: Focal masses may grow to several centimeters
Morphology
- 75% of pleural mesotheliomas are diffuse desmoplastic type (usually malignant)
  - Diffuse disease may envelop abdominal viscera
- Remainder are focal, producing large mass with scattered pleural/peritoneal nodules

Imaging Recommendations

Best imaging tool
- Although not routinely used, PET/CECT may offer best information for diagnosis, staging, and response to therapy
- CT sensitive but not specific for invasion
Protocol advice
- Modified breathing algorithms to reduce misregistration along diaphragm
  - Coronal reformation of CECT may aid in detection of mesothelioma
- Water or oral contrast to distend bowel loops

CT Findings

Pleural disease best imaged with contrast enhancement at 45-60 second delayed scan time
Extent of pleural and extrapleural involvement is well-evaluated on CT
Most common findings
- Irregular, unilateral thickening of the pleura in a nodular, concentric, or plaque-like configuration
- Pleural effusion
  - Pleural effusion commonly fills 1/3 to 2/3 of hemithorax
Pleural thickening may present with
- Greater thickness at bases
- Thickening of interlobular fissures
- Calcification
- Contraction of hemithorax in 40%
- Chest wall invasion (difficult to detect based on irregularity alone)
- Bilaterality in 20%
Findings of local invasion
- Irregular contour along inferior aspect of diaphragm
- Invasion of endothoracic fat
- Loss of normal adjacent fat planes
- Infiltration along biopsy tract or surgical incision seen in 20%
- Greater than 50% circumferential encasement of mediastinal structure
Findings of extrathoracic spread
- Soft tissue mass encasing hemidiaphragm
- Absence of fat plane between diaphragm and abdominal organs
- Liver metastases may rarely present with diffuse calcification
Findings typical of malignant vs. benign disease
- Involvement of mediastinal pleura
- Nodular pleural thickening
- Greater than 1 cm thickening of parietal pleura
- Circumferential pleural thickening
Response to therapy
- Modified RECIST criteria evaluating thickness of involved pleura
  - Must decrease by 30% to indicate partial response to therapy
- In one study, 47% of partial responders imaged with CT were detected after one cycle of chemotherapy

Nuclear Medicine Findings

Initial Diagnosis
- Mesothelioma generally FDG avid
  - Mild or absent FDG uptake has been reported in some patients with mesothelioma of epithelial subtype
- SUV of 2.0 used as cutoff for suspicion of malignancy in pleural lesions
- FDG PET pattern and intensity do not allow differentiation of
  - Subtypes of malignant pleural mesothelioma
  - Mesothelioma from adenocarcinoma or sarcoma
Staging
- PET/CT suited for
  - Detection of unsuspected nodal and occult distant metastases
  - Particularly useful for staging mediastinal nodal involvement
  - Sensitivity, specificity for T4 disease: 67% and 93%
  - PET alone sensitivity 19%
- Limited for evaluation of nodal mets
  - 38% sensitivity in one study
  - Insensitive for microscopic disease
  - False positives from inflammatory/infectious etiologies
  - e.g., talc pleurodesis, benign inflammatory pleuritis, parapneumonic effusion, tuberculous pleuritis
- Limited for determining presence/extent of local tumor invasion
Response to therapy
- FDG PET accurate for prediction of response following one cycle of chemotherapy
- Defining tumor volume is laborious and error-prone due to “rind-like” morphology of mesothelioma
  - Tumor glycolysis volume (TGV) has been used effectively for accurate prognostic information
  - TGV superior to max SUV or CT response after one cycle of chemotherapy for predicting survival
Morphology
- Tumors at earlier stage tend to have focal or linear patterns
- Mixed and encasing patterns are indicative of more advanced disease
PET/CT and CT alone differ in TNM classification in up to 50% of patients
- 50% of discordances clinically relevant
- PET/CT upstaged 12% of patients with noncurable disease and downstaged 12% of patients to curable disease
Prognosis
- Best: Low SUV and epithelial histology; median survival 24 months
- Worst: High SUV and sarcomatoid histology; median survival 14 months
- High SUV tumors associated with 3.3x higher risk of death than low SUV tumors
- Intensity of FDG uptake by primary shown to have poor correlation with histologic grade, good correlation with surgical stage

DIFFERENTIAL DIAGNOSIS

Asbestos Related Pleural Disease

Typically less FDG avid
Often indistinguishable from mesothelioma on CT
Look for absence of malignant findings
- Continuous pleural “rind”
- Pleural nodularity
- Thickening > 1 cm
- Involvement of mediastinal pleura
Benign disease may also demonstrate nodular pleural thickening
Biopsy recommended for equivocal cases
Calcified plaques are sign of asbestos exposure, not precursor to mesothelioma

Congestive Heart Failure

Interstitial and perivascular edema may develop, most prominent at lung bases
Large pleural effusions and alveolar edema in perihilar and lower lobe distribution
Correlate clinically with follow-up imaging

Chronic Organized Empyema