## Imaging Features of Malignant Pleural Effusion ### CT Findings — The Gold Standard **Key Point:** Pleural thickening >1 cm with nodular or irregular contours is the most specific imaging sign of malignant pleural involvement. This reflects tumor infiltration and pleural fibrosis. ### Comparison of Imaging Features | Feature | Malignant | Benign (Heart Failure/Pneumonia) | |---------|-----------|----------------------------------| | **Pleural thickening** | >1 cm, nodular, irregular | Thin or absent (<3 mm) | | **Pleural nodules** | Present, enhancing | Absent | | **Mediastinal LAD** | May be present (not specific) | Absent or minimal | | **Effusion volume** | Variable, not discriminatory | Variable, not discriminatory | | **Distribution** | Often unilateral | Often bilateral (CHF) | | **Associated findings** | Lung masses, rib involvement | Cardiomegaly, pulmonary edema | **High-Yield:** On **CT chest**, pleural thickening >1 cm with nodularity or enhancement is highly suggestive of malignancy and warrants pleural biopsy or thoracentesis with cytology. ### Clinical Approach 1. **Plain radiography** shows the effusion but lacks specificity for malignancy. 2. **CT chest with contrast** reveals pleural thickening, nodules, and enhancement—key discriminators. 3. **Pleural biopsy** (image-guided or thoracoscopic) is the gold standard for diagnosis when imaging suggests malignancy. **Clinical Pearl:** Benign effusions (CHF, pneumonia) typically have thin, smooth pleura; malignant effusions show thick, nodular, or irregular pleural surfaces due to tumor infiltration. **Mnemonic: PNEU** — **P**leural thickening >1 cm, **N**odules, **E**nhancement, **U**nilateral distribution (in malignancy). [cite:Robbins 10e Ch 15] 
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