Diagnostic Ability of FDG-PET/CT in the Detection of Malignant Pleural Effusion

Our plain-English summary of Diagnostic Ability of FDG-PET/CT in the Detection of Malignant Pleural Effusion, by R. Nakajima, K. Abe, S. Sakai (Medicine, 2015).

The study

• Authors: R. Nakajima, K. Abe, S. Sakai
• Journal: Medicine
• Published: 2015;94(29):e1010
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

We investigated the role of F-18 fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) for the differential diagnosis of malignant and benign pleural effusion. We studied 36 consecutive patients with histologically proven cancer (excluding malignant mesothelioma) who underwent FDG-PET/CT for suspected malignant pleural effusion. Fourteen patients had cytologically proven malignant pleural effusion and the other 22 patients had either negative cytology or clinical follow-up, which confirmed the benign etiology. We examined the maximum standardized uptake values (SUV max) of pleural effusion and the target-to-normal tissue ratio (TNR), calculated as the ratio of the pleural effusion SUV max to the SUV mean of the normal tissues (liver, spleen, 12th thoracic vertebrae [Th12], thoracic aorta, and spinalis muscle). We also examined the size and density (in Hounsfield units) of the pleural effusion and pleural abnormalities on CT images. TNR (Th12) and increased pleural FDG uptake compared to background blood pool were significantly more frequent in cases with malignant pleural effusion (P < 0.05 for both). The cutoff TNR (Th12) value of >0.95 was the most accurate; the sensitivity, specificity, and accuracy for this value were 93%, 68%, and 75%, respectively. FDG-PET/CT can be a useful method for the differential diagnosis of malignant and benign pleural effusion.

In plain English

This retrospective study, from a hospital in Tokyo, Japan, tested whether FDG-PET/CT scans can tell cancer-related (malignant) fluid around the lungs from non-cancer (benign) fluid in people who already had cancer. It does not deal with asbestos, and patients with malignant mesothelioma were excluded. Of 100 cancer patients scanned for suspected malignant pleural effusion between January 2013 and April 2014, 36 were included: 14 had malignant effusions and 22 had benign ones. The scans measured how much tracer the fluid took up compared with normal tissues. Uptake measures were significantly higher in malignant effusions. Fluid density, fluid size and pleural abnormalities on CT did not differ significantly between the groups. A ratio of fluid uptake to uptake in the 12th thoracic vertebra, with a cutoff above 0.95, showed 93% sensitivity, 68% specificity and 75% accuracy. Increased pleural uptake appeared in 8 of 14 malignant and 2 of 22 benign cases. The authors concluded that FDG-PET/CT can be a useful noninvasive method for this distinction. They noted the small number of patients and the retrospective design.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective diagnostic accuracy study of an imaging test (FDG-PET/CT) at a single institution
• Who was studied: 36 consecutive patients with histologically proven cancer (excluding malignant mesothelioma) who had FDG-PET/CT for suspected malignant pleural effusion at the authors' institution (Tokyo Women's Medical University, Japan) between January 2013 and April 2014. They were 25 men and 11 women aged 41 to 87, mean age 69. They were selected from 100 patients whose records were reviewed. 14 had malignant pleural effusion. 22 had benign effusion: 9 confirmed by at least 2 negative cytology tests and 13 by more than 6 months of clinical follow-up.
• Main results:
  • Between patients with malignant and benign effusion, there were no significant differences in age, sex, blood sugar, fluid density, fluid size, or pleural abnormalities on CT.
  • All uptake ratios (TNR) and the maximum uptake value (SUVmax) of the fluid were significantly higher in patients with malignant pleural effusion than in those with benign effusion.
  • Increased pleural FDG uptake was seen in 8 of the 14 patients with malignant effusion and 2 of the 22 patients with benign effusion. The 2 benign cases had chronic empyema and were counted as false positives.
  • For telling malignant from benign effusion, the ratio of fluid uptake to 12th thoracic vertebra uptake, with a cutoff of 0.95, had 93% sensitivity, 68% specificity and 75% accuracy.
  • Increased pleural FDG uptake had 57% sensitivity, 91% specificity and 78% accuracy.
  • In logistic regression analyses, the 12th thoracic vertebra uptake ratio and increased pleural FDG uptake were the best-fitting measures for distinguishing malignant from benign effusion.
• The authors' conclusion: The authors concluded that FDG-PET/CT is noninvasive and can be a useful method for distinguishing malignant from benign pleural effusion in patients with cancer. They also concluded that a 12th thoracic vertebra uptake ratio above 0.95 would be the most accurate measure for identifying malignant effusion.
• Limitations the authors state:
  • The number of patients was relatively small (36), because of strict inclusion criteria.
  • The study was retrospective, and the authors said prospective studies with more patients are needed to validate the results.
  • Not all patients had an open pleural biopsy as a standard procedure.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Effusion, Differential Diagnosis, Malignant Mesothelioma, Cytology, Etiology.

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