Background: The diagnosis of malignant mesothelioma is a challenging medical question CT often cannot differentiate between benign diffuse pleural thickening and malignant mesothelioma.

Background: The diagnosis of malignant mesothelioma is a challenging medical question CT often cannot differentiate between benign diffuse pleural thickening and malignant mesothelioma, while thoracentesis and CT-guided biopsies are insensitive. We have assessed the value of positron emission tomography (PET) with 2-fluoro-2-deoxy-D-glucose (FDG) in the evaluation of malignant mesothelioma.

Methods: Twenty-eight consecutive patients referr for the evaluation of suspected malignant mesothelioma were evaluated at FDG-PET imaging. Measured attenuation correction was performed in 26 of 28 cases for quantitation with the standardized uptake value (SUV) means The results of PET imaging were compared with those of video-assisted thoracoscopy or surgical biopsies.

Results: Surgical biopsy specimens confirmed the demeanor of malignant disease in 24 patients and demonstrated benign processe in the remaining four. The uptake of FDG was significantly higher in malignant than in benign lesions (SUV=49 [+ or -] 29 and SUV= 14 [+ or -] 06 respectively; p [is les than] 00001) With a SUV cutoff of 20 to differentiate between malignant and benign disease, a sensitivity of 91% and a specificity of 100% could be achieved, although the activity in a certain quantity of epithelial mesotheliomas tended to be obstruct to this threshold. FDG-PET images provided of the highest order delineation of the active tumor sites. Hypermetabolic lymph node involvement was noted in succession FDG-PET images in 12 patients, 9 of which appeared normal in succession CT scans. Histologic examination in six patients confirmed malignant nodal disease in five cases and indicated granulomatous lymphadenitis in one

Conclusion: In this highly choiceed population, FDG-PET imaging was a sensitive way to identify malignant mesothelioma and determine the length of the disease process.

(CHEST 1998; 114:713-722)

Key words: FDG; malignant mesothelioma; metabolic imaging; positron emission tomography

Abbreviations: FDG= fluorodeoxyglucose; PET=positron emission tomography; SUV= standardized uptake value

The treatment of patients with asbestos-related pleural disease is challenging. Pleural manifestations of asbestos prospect include calcifications, plaques, benign effusion, and diffuse thickening.[1] Diffuse pleural thickening can show either a benign or a malignant proces In addition, many infectious disorders of the like kind as tuberculosis or empyema can cause fibrothorax, which cannot be easily differentiated from pleural malignancies. Cross-sectional imaging manners such as CT or MRI, are helpful in identifying the location and size of the involved areas. However, these modalities are commonly unable to discriminate between malignant disease and benign processes[2] Using morphologic criteria, the sensitivity and specificity of CT to predict the malignant nature of diffuse pleural lesions are 72% and 83% respectively.[3] With MRI, gentle signal intensity on long repetition time images is associated with benign disease; sensitivity and specificity figures of 100% and 87% respectively, have been reported with this technique to identify malignant disease.[4] Radionuclide imaging with [sup.67]Gallium citrate has also been used for this purpose[5] with a sensitivity of 86% and a specificity of 81% However, the resolution of imaging with gallium is poor, in the range of 15 to 20 cm making it suboptimal for staging lymph node involvement and for the characterization of small pleural lesions. Because of these limitations, gallium scanning has not been accepted for routine evaluation of mesothelioma.

Positron emission tomography (PET) utilizing fluorodeoxyglucose (FDG) is a powerful diagnostic tool for the diagnosis and treatment of patients with cancer.[6] FDG-PET has a proven utility in discriminating benign from malignant lung nodules.[7-9] Similarly, FDG-PET could potentially differentiate benign from malignant pleural lesions, stage the volume of disease involvement, and help in the selection of biopsy sites by means of identifying the most metabolically active lesions.

MATERIALS AND METHODS

Patient Selection

The patient population consisted of 28 consecutive patients referr for the evaluation of pleural disease and suspected malignant mesothelioma. The disease was suspected from clinical symptoms and onward the basis of chest radiograph or CT scan results: effusion, pleural masses, or pleural thickening. The FDG-PET investigation was obtained as part of the clinical evaluation to assess the carriage of malignant disease and to determine the stretch of tumor involvement. Informed co-operation was obtained in all patients before the performance The patients also underwent chest radiograph and CT evaluation, and pleural fluid cytologic examination. The final diagnosis was established according to thoracoscopic biopsy specimen in 21 make liables pleural biopsy specimen in 4 pleural fluid cytology in 1 pleural decortication in 1 and clinical follow-up in 1 Combined emission and transmission scanning was complet in 26 of 28 make submissives In the remaining two make subordinates only the emission scan was available.

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