PET/CT scan and malignant pleural effusion: are we ready to rely less on imaging?

<bold>Introduction:</bold> Medical thoracoscopy (MT) with pleural biopsies is the gold standard for diagnosis of pleural diseases. PET-CT negativity can delay diagnosis of malignant pleural effusions (MPE). <bold>Aim and Objectives:</bold> To determine whether MT should be considered to investigate pleural effusions of unknown etiology despite PET-CT negativity. <bold>Methods:</bold> 42 patients with MPE who performed PET/CT scan prior procedure were consecutively enrolled between January 2022 and January 2024. All of them received a histological diagnosis of pleural malignancy via MT and pleural biopsies. Patients were divided in 2 different groups based on pleural metabolism at PET-CT: negative (group 1) and positive (group 2). Gender, age, side and diagnosis were evaluated. <bold>Results:</bold> 10/42 patients (24%) had a histological diagnosis of malignancy despite PET-CT negativity. Gender distribution was similar in two groups, with male predominance (80% - 20% vs 81% - 19%); median age was similar (74 vs 73 years) with the same interquartile range (8 vs 8 years). In group 1 most cases concerned left side (60%), whereas right side was more frequent in group 2 (47%). In group 1 most frequent histological findings were metastasis (3 lung, 1 pancreas, 1 breast), followed by mesothelioma (4) and lymphoma (1). In group 2, histological findings were mesothelioma (18), metastasis (7 lung, 2 breast, 2 kidney, 1 pancreas, 1 thymus), myeloma (1). <bold>Conclusions:</bold> In our experience, PET-CT negativity in MPE is a frequent finding and PET/CT scan should not be considered during diagnostic workup for patients with suspected pleural malignancy.