Can PET/CT be used more effectively in pleural effusion evaluation?

Sometimes, characterization of pleural effusion (PE) can be challenging especially in patients whom invasive procedures/recurrent invasive procedures cannot be performed. The main purpose of the study is to answer this question, Can ¹⁸F-FDG-PET/CT contribute to reduction in the number of invasive procedures or patients undergoing to invasive procedures? Results may increase the effectiveness of patient management by facilitating clinical decision-making, especially in patients who cannot undergo invasive/recurrent invasive procedures.

Sixty-seven patients' ¹⁸F-FDG-PET/CT, pleural fluid cytologies (PFCs) and, if any, pleural biopsies were re-assessed. If patient's PFC/biopsy was malignant, effusion was considered as malignant. If two consecutive PFCs were negative in patients without biopsy, effusion was considered as benign. Characterization was based on consensus with baseline/follow-up ¹⁸F-FDG-PET/CT and clinical parameters in patients with one negative PFC (n = 6).

None of the ¹⁸F-FDG-PET/CT parameters could characterize PE alone. However, if PE maximum standardized uptake value (SUV_max) > 1.3 or PE SUV_max/mean standardized uptake value of mediastinal blood pool (MBP SUV_mean) > 1.2 was combined with at least one of the following, specificity and positive predictive value (PPV) were 100%, accuracy was around 90%. Diffuse-nodular/nodular pleural thickness, post-obstructive atelectasis, nodule/mass with SUV_max > 2.5 in lung, multiple pulmonary nodules. All 29 patients who had SUV_max > 1.3 together with at least one of the mentioned four parameters diagnosed malignant pleural effusion (MPE). However, sensitivity and negative predictive value (NPV) were still insufficient.

Patients who have contraindications for invasive diagnostic methods, and meet the aforementioned criteria may be considered as MPE primarily. On the other hand, if PE SUV_max < 1.3 or PE SUV_max/MBP SUV_mean < 1.2 with the negativity of the all four parameters mentioned above, it is difficult to say that this can be considered as benign pleural effusion (BPE) according to our results.