18-FDG positron emission tomography in the evaluation of malignant pleural diseases - a pilot study

The diagnostic approach to pleural diseases may be difficult. The CT scan, which is the current diagnostic technique, has limited accuracy both in the differentiation between benign and malignant pleural diseases and in the diagnosis of primary and metastatic pleural neoplasms. Invasive procedures, such as thoracoscopy, are therefore frequently required to complete the diagnostic approach. The increasing incidence of malignant pleural mesothelioma has led to the development of new treatment strategies, which still need to be fully validated. There is, therefore, a need for new diagnostic techniques that can lead to a definite diagnosis and a satisfactory evaluation of the response to treatment. Encouraging results have been reported with the F-18-labeled analogue of 2-deoxyglucose (18-FDG) positron emission tomography (PET) in the evaluation of chest tumors such as lung cancer. The aim of this study was to evaluate the role of 18-FDG PET in the diagnostic assessment of pleural diseases.

Patients with CT scan evidence of pleural thickening, or fluid, entered a study to evaluate the accuracy of 18-FDG PET in diagnosing pleural diseases. Image analysis was performed both with visual interpretation and using a semiquantitative method, standardized uptake values (SUV), on coronal, sagittal and axial reconstructions. The results of PET imaging were compared to histological data. PET was also performed before and after treatment in patients who underwent chemotherapy to evaluate the accuracy of this technique in the assessment of the response.

Fourteen patients entered the study. Histology demonstrated a malignant pleural disease in 13 patients; malignant pleural mesothelioma in ten patients, adenocarcinoma in two and liposarcoma in one. Benign pleural disease was diagnosed in the remaining patient. PET assessment demonstrated significant 18-FDG uptake in 12 of the 13 patients with a malignant disease, also revealing distant metastases in two of them. A false-negative result was observed in a patient with an epithelial mesothelioma. The overall accuracy was 92%. A benign pleural disease without significant uptake was correctly diagnosed in another patient. An aspecific uptake was observed in two patients who had undergone pleurectomy and intrapleural chemotherapy. A decreased tracer uptake was observed after chemotherapy in four patients.

These preliminary results demonstrate that 18-FDG PET may have a great potential, both in the differential diagnosis of pleural diseases and in the evaluation of the response to treatment. At present, however, histological thoracoscopic diagnosis remains mandatory before planning treatment. Further studies in larger groups of patients are needed to draw definite conclusions on the role of PET in the assessment of pleural diseases.