Pleural Malignancy

Three entities account for greater than 99% of all pleural malignancy:

• Metastatic Disease (commonly breast, lung, ovary, gastric, and melanoma)
• Lymphoma
• Mesothelioma

Both lymphoma and metastatic disease typically present as either uni-focal or multi-focal areas of hypermetabolic pleural thickening, often nodular in CT appearance. 

Mesothelioma usually presents with large regions (non-focal) of FDG-avid pleural thickening, often circumferentially surrounding a lung. The pleural thickening can be nodular or smooth.  An associated pleural effusion is usually present.

False Positives:

Talc Pleurodesis: 

Talc pleurodesis is performed to obliterate the pleural space, typically in cases of recurrent pleural effusions or pneumothorax. Talc causes an intensely avid inflammatory reaction, which fuses the parietal and visceral pleura.  The hypermetabolic appearance of talc pleurodesis may persist for decades after the procedure.

As oncology patients very commonly require pleurodesis, radiologists must be very comfortable with its PET/CT characteristics. 

Fortunately, its characteristic hyperdense appearance on CT readily distinguishes it from pleural malignancy (knowing the patient’s history also helps…).

Imaging Characteristics:

• Intensely avid pleural thickening, usually with nodular components.
• Non-uniform distribution; much of the pleura may be spared.
• Hyperdense appearance on CT makes the diagnosis.

Be mindful that patients who have undergone talc pleurodesis may also have co-existing active plural malignancy in other areas of their pleura. Distinguishing and localizing these separate entities will help the clinician direct appropriate therapy. 

Inflammatory FDG-Avid Pleural Thickening After Pneumonectomy:

FDG-avid pleural thickening after pneumonectomy is not uncommon and can persist for years. This thickening usually demonstrates fairly uniform uptake, typically mild to moderately avid. 

Unless a focal component of this thickening demonstrates FDG-uptake significantly greater than the remainder of the affected pleura (“you can put your finger on the spot”), the finding is “presumed inflammatory”.  Follow up, however, may be warranted.

Infection/Empyema:  

Such infection can cause intensely avid pleural thickening. The patient’s clinical history, however, usually leads one to the proper diagnosis in these cases. Follow-up may be required.

Malignant Pleural Effusion:

Most commonly associated with lung, breast, ovary and lymphoma.  Most malignant effusions demonstrate only moderate metabolic activity, rarely above background uptake within the liver.  

It is reasonable to raise a suspicion of a malignant effusion whenever the uptake approaches that of the liver.