Victor H Gerbaudo

Background: Malignant pleural mesothelioma is an aggressive neoplasm with a highly variable course. This pilot study evaluated the significance of the pattern, intensity and kinetics of ¹⁸F-FDG uptake in mesothelioma in the context of histopathology and surgical staging. Methods: Sixteen consecutive patients with pleural disease on CT scan underwent ¹⁸F-FDG imaging. Imaging was performed with a dual detector gamma camera operating in coincidence mode. Semiquantitative image analysis was performed by obtaining lesion-to-background ratios (¹⁸F-FDG uptake index) and calculating the increment of ¹⁸F-FDG lesion uptake over time (malignant metabolic potential index (MMPi)). Results: Twelve patients had histologically proven malignant mesotheliomas (10 epithelial, two sarcomatoid). Thirty two lesions were positive for tumour. Patterns of uptake matched the extent of pleural and parenchymal involvement observed on CT scanning and surgery. Mean (SD) ¹⁸F-FDG uptake index for malignant lesions was 3.99 (1.92), range 1.5–9.46. Extrathoracic spread and metastases had higher ¹⁸F-FDG uptake indices (5.17 (2)) than primary (3.42 (1.52)) or nodal lesions (2.99 (1)). No correlation was found between histological grade and stage. The intensity of lesion uptake had poor correlation with histological grade but good correlation with surgical stage. ¹⁸F-FDG lesion uptake increased over time at a higher rate in patients with more advanced disease. The MMPi was a better predictor of disease aggressiveness than the histological grade. Conclusions: This pilot study suggests that the pattern, intensity, and kinetics of ¹⁸F-FDG uptake in mesothelioma are good indicators of tumour aggressiveness and are superior to the histological grade in this regard.

Malignant pleural mesothelioma is an aggressive primary neoplasm for which early detection and accurate staging are known diagnostic challenges. The role of (18)F-FDG dual-head gamma-camera coincidence imaging ((18)F-FDG-CI) is yet to be defined. The purpose of this study was to evaluate the usefulness of (18)F-FDG-CI in the assessment of malignant pleural mesothelioma using histopathology as the gold standard. Fifteen consecutive patients with CT scan evidence of pleural thickening, fluid, plaques, or calcification underwent (18)F-FDG imaging 1.5 h after the intravenous administration of 370 MBq (18)F-FDG. Imaging was performed with a dual-head gamma camera equipped with 2.54-cm-thick NaI crystals operating in coincidence mode. Using an iterative algorithm, whole-body images were reconstructed as transaxial, sagittal, and coronal images. No attenuation correction was applied. The results of (18)F-FDG-CI scans were compared with CT and with histopathologic diagnosis. Eleven of 15 patients had histologically proven malignant mesotheliomas (10 epithelial, 1 sarcomatoid). All 11 primary tumors were detected by (18)F-FDG, and absence of disease was confirmed in the 4 patients who were disease free. Thirty-four lesions were biopsied; among these, 29 were found to be positive for tumor. (18)F-FDG was true-positive in 28 lesions, true-negative in 4, false-negative in 1 (0.5 cm in diameter), and false-positive in 1 (inflammatory pleuritis). The smallest lesion detected was 0.8 cm. For biopsied lesions, overall sensitivity, specificity, and accuracy for (18)F-FDG-CI were 97%, 80%, and 94% respectively, compared with 83%, 80%, and 82% for CT. Twenty-one of 29 positive lesions involved the pleura, lung parenchyma, or chest wall and were all (18)F-FDG avid. In the mediastinum, (18)F-FDG-CI detected 7 of 8 biopsy-positive lesions (88%), whereas CT was positive in 6 of 8 lesions (75%). (18)F-FDG identified extrathoracic metastases in 5 patients, excluding them from surgical therapy. These preliminary results suggest that (18)F-FDG-CI appears to be an accurate method to diagnose and to define the extent of disease in patients with diffuse malignant pleural mesothelioma.