Abstract
Positron Emission Tomography/Computed Tomography (PET/CT) is well recognized as an important modality to detect malignant neoplasm, which plays a crucial role in the assessment of patients with malignant pleural mesothelioma (MPM). T1a category of IMIG classification refers to an early tumor that involves the parietal pleura only. And, there are a certain number of patients with more earlier clinical stage than T1a, i.e., radiological and thoracoscopical T0 stage. Those patients with T0 stage have neither visible pleural tumor nor pathologic PET/CT findings, and they are sometimes misdiagnosed as nonspecific pleuritis after a complete investigation including thoracoscopical biopsies. Those patients will turn out to be malignant during follow-up period. The purpose of this study was to investigate when tumor growth came to be detectable with PET/CT in patients with very early clinical stage of MPM whose PET/CT had been negative. Seven histologically-proven MPM patients with T0/T1a clinical stage were followed up with PET/CT (Epithelioid/unknown; 6/1). A surgical thoracoscopy(VATS) or medical thoracoscopy with narrow band and autofluorescence imaging in addition to white light had been performed to obtain adequate materials of pleura and to diagnose T1-stage macroscopically. No patients had received talc pleurodesis. The initial thoracic CT scans showed pleural effusion without thickening of pleura, and all of the initial PET/CT evaluation was negative. The radiological examinations, including PET/CT and contrast and/or plain CT for loco-regional disease were reviewed to see tumor growth that came to be able to detect with PET scan. Interpretation of positive PET scan for malignancy is SUV>2.5. The median interval between the initial PET/CT and the follow-up PET scan to come to identify malignant nodules for the first time was 32 months (5 - 46 months). Two patients with epithelioid and unknown MPM showed a positive finding of PET scan at the site of pleural intervention (thoracoscopy/thoracentesis), of which interval were 5 and 8 months, respectively. PET-positive pleural nodules, 5.1 ～ 8.2 mm in diameter, were demonstrated in 4 patients. And, a diffuse pleural thickening with positive PET scan, 6.5 mm in thickness, was shown in 1 patient with epithelioid MPM. PET/CT is a valuable modality for detecting the progression of T0/T1a tumors > 5 mm in diameter. Interval between PET-negative T0/T1a tumor and PET-positive tumor growth is more than 2 years (median; 32 months), and tumor seeding at the site of previous pleural intervention is an early manifestation of MPM.
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