What is the diagnosis for a patient with pleural fluid suspicious for adenocarcinoma, but no distinct mass on computed tomography (CT) scan, and interval slight further resolution of right pleural effusion with passive atelectasis of the adjacent lung?

From the Guidelines

The patient with pleural fluid suspicious for adenocarcinoma without a distinct mass on CT should undergo further diagnostic evaluation, starting with thoracentesis for cytology if not already done, followed by pleural biopsy (either CT-guided or thoracoscopic) to confirm the diagnosis, as recommended by the American College of Chest Physicians evidence-based clinical practice guidelines 1. In this situation, the presence of pleural fluid suspicious for adenocarcinoma without a distinct mass on CT suggests a possible malignancy that may be originating from a small primary tumor or metastatic disease. The CT findings of resolving pleural effusion, atelectasis, and inflammatory changes suggest an ongoing process that requires monitoring. The presence of mediastinal and hilar lymph nodes, though described as reactive, should be evaluated for potential malignant involvement. Ultrasound-guided thoracentesis is recommended to improve the success rate and decrease the rate of pneumothorax, as it has been shown to have a higher sensitivity and specificity in differentiating malignant from benign effusions 1. Pleural fluid cytology is a more sensitive diagnostic test than percutaneous pleural biopsy, with a mean sensitivity rate of about 72% when at least two pleural fluid specimens are submitted 1. While waiting for definitive diagnosis, oncology consultation should be initiated to prepare for potential treatment planning if adenocarcinoma is confirmed. Some key points to consider in the diagnostic workup include:

• The use of PET-CT scanning to identify any occult primary tumor that may not be visible on conventional CT
• Focused examination of common primary sites for adenocarcinoma presenting with pleural effusion, including lung, breast, ovary, and gastrointestinal tract
• The potential for malignant involvement of the mediastinal and hilar lymph nodes, despite their description as reactive
• The importance of monitoring the ongoing process suggested by the CT findings of resolving pleural effusion, atelectasis, and inflammatory changes.

From the Research

Diagnosis of Malignant Pleural Disease

• The diagnosis of malignant pleural disease is crucial in the care of patients with cancer, and a one-size-fits-all approach to diagnosis may lead to delays in care 2.
• Pleural fluid cytology has a limited value in diagnosing malignant pleural disease, and repeated thoracenteses may not be effective in many cases 2.
• Medical thoracoscopy is a relatively safe diagnostic modality with high sensitivity and should be considered in patients with a nondiagnostic thoracentesis 2.

Adenocarcinoma Spectrum Lesions

• Adenocarcinoma has become the most prevalent lung cancer sub-type, and its frequency is increasing 3.
• The earliest stages in the development of lung adenocarcinomas are visible using modern computed tomography (CT) as ground glass nodules, which can progress over time to become invasive lung adenocarcinomas 3.
• Lesions in this developmental pathway are termed 'adenocarcinoma spectrum' lesions, and understanding their development can create treatment targets 3.

Predicting the Nature of Pleural Effusion

• A predictive model based on 18F-FDG PET/CT can be used to diagnose the nature of pleural effusion in patients with lung adenocarcinoma 4.
• The model uses PET/CT parameters and clinical information to estimate the independent predictive factors of malignant pleural effusion (MPE) and to establish a predictive model 4.
• The predictive model showed good discrimination and calibration, and can be used to differentiate MPE from benign pleural effusion (BPE) in patients with lung adenocarcinoma 4.

Clinical Application of PET/CT

• PET/CT can be clinically useful for adenocarcinoma with bronchioloalveolar carcinoma features, as it can predict the incidence of intrathoracic lymph node metastases at preoperative stages 5.
• The maximum standardized uptake value (SUVmax) obtained by PET/CT can be used to predict the incidence of intrathoracic lymph node metastases, and has significant inverse correlation with the ratio of BAC component 5.

Management of Malignant Pleural Effusion

• Malignant pleural effusion is a common complication of cancer and denotes a poor prognosis, and current management is palliative 6.
• Thoracic computed tomography scans and ultrasound are helpful in distinguishing malignant from benign effusions, and pleural fluid cytology is diagnostic in about 60% of cases 6.
• Indwelling pleural catheter insertion is an increasingly acceptable first-line treatment for recurrent symptomatic malignant pleural effusion, and can be used as an alternative to chest drain insertion and talc pleurodesis 6.