Mesothelioma



Mesothelioma


Todd M. Blodgett, MD

Janet Durick, MD

Sanjay Paidisetty, BS









Graphic shows nodular thickening of the right pleura image, representing mesothelioma.






Coronal PET shows increased FDG activity image 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

Sep 22, 2016 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Mesothelioma

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