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

Objective: The diagnostic approach to pleural diseases may be difficult. Th e CT scan, which is the current diagnostic technique, has limited accuracy both in the differentiation between benign and malignant pleural diseases a nd in the diagnosis of primary and metastatic pleural neoplasms. Invasive p rocedures, such as thoracoscopy, are therefore frequently required to compl ete 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 diagn ostic techniques that can lead to a definite diagnosis and a satisfactory e valuation of the response to treatment. Encouraging results have been repor ted with the F-18-labeled analogue of a-deoxyglucose (18-FDG) positron emis sion 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 diagn ostic assessment of pleural diseases. Methods: Patients with CT scan eviden ce of pleural thickening, or fluid, entered a study to evaluate the accurac y of 18-FDG PET in diagnosing pleural diseases. Image analysis was performe d both with visual interpretation and using a semiquantitative method, stan dardized uptake values (SUV), on coronal, sagittal and axial reconstruction s. The results of PET imaging were compared to histological data. PET was a lso performed before and after treatment in patients who underwent chemothe rapy to evaluate the accuracy of this technique in the assessment of the re sponse. Results: Fourteen patients entered the study. Histology demonstrate d a malignant pleural disease in 13 patients; malignant pleural mesotheliom a in ten patients, adenocarcinoma in two and liposarcoma in one. Benign ple ural disease was diagnosed in the remaining patient. PET assessment demonst rated significant 18-FDG uptake in 12 of the 13 patients with a malignant d isease, also revealing distant metastases in two of them. A false-negative result was observed in a patient with an epithelial mesothelioma. The overa ll accuracy was 92%. A benign pleural disease without significant uptake wa s 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 patient s. Conclusions: These preliminary results demonstrate that 18-FDG PET may h ave a great potential, both in the differential diagnosis of pleural diseas es and in the evaluation of the response to treatment. At present, however, histological thoracoscopic diagnosis remains mandatory before planning tre atment. Further studies in larger groups of patients are needed to draw def inite conclusions on the role of PET in the assessment of pleural diseases. (C) 2000 Elsevier Science B.V. All rights reserved.