C80-24 A Pseudo-transudative Pleural Effusion in Hepatobiliary Adenocarcinoma - A Case Report and Literature Review

Abstract Introduction Light’s criteria classify pleural effusions as transudative or exudative; however, systemic or malignant processes may occasionally alter pleural fluid characteristics. Although malignant pleural effusions (MPE) are typically exudative, pseudo-transudative variants that biochemically are transudative but cytology-positive for malignancy account for 6%. We report an uncommon presentation of hepatobiliary adenocarcinoma with transudative appearing yet cytology-proven malignant pleural effusion. Case Description A 65-year-old Hispanic woman with metastatic cholangiocarcinoma on palliative chemotherapy, obstructive jaundice post-biliary stenting, diabetes, and chronic kidney disease developed acute dyspnea and transient hypotension during biliary drain exchange. On arrival to the emergency department, she was hemodynamically stable. Laboratory evaluation: leukocytosis (24.3 × 109/L), anemia (8.7 g/dL), thrombocytopenia (131 × 109/L), elevated creatinine (2.04 mg/dL), and hypoalbuminemia (1.7 g/dL). CT imaging revealed stable biliary drains, moderate intrahepatic dilation, and a large left pleural effusion with compressive atelectasis. Left chest tube drained 3.35 L of cloudy orange fluid with transudative parameters (glucose 116 mg/dL, pleural LDH 66 U/L; serum LDH 262 U/L) and 74% neutrophils. Pleural and blood cultures were sterile, but cytologic analysis revealed malignant cells consistent with metastatic hepatobiliary adenocarcinoma. A tunneled PleurX catheter placed for ongoing management, and subsequent liver biopsy confirmed advanced cholangiocarcinoma. The patient discharged in stable condition with outpatient oncology follow-up. Discussion MPEs are typically exudative due to pleural infiltration or lymphatic obstruction; however, a small proportion fewer than 6% demonstrate transudative features, termed pseudo-transudative effusions. Mechanisms include lymphatic obstruction without direct pleural invasion, coexisting systemic disorders such as heart failure, cirrhosis, or renal dysfunction, and tumor-related atelectasis resulting in low-protein ultrafiltrates. Assi et al. reported that only 1% of cytology-confirmed MPEs were transudative, whereas Ryu et al. identified a prevalence of about 5%, predominantly in patients with concurrent systemic transudative conditions. Gonlugur et al. similarly found transudative effusions in 1.5% of mesotheliomas and 6.8% of metastatic malignancies, underscoring the rarity of this entity. Predictive models proposed by Ferreiro et al., incorporating radiologic findings and biomarkers such as carcinoembryonic antigen, may enhance recognition of malignant transudates but require further validation. Although Light’s criteria remain the foundation of pleural fluid assessment, this report demonstrates a unique diagnostic discordance between pleural fluid chemistry and cytology in malignant effusions from advanced hepato-biliary carcinoma. It also reinforces the clinical value of comprehensive evaluation by integrating laboratory, cytologic, and radiologic data to improve diagnostic accuracy and guide MPE management. References: PMIDs 1. 9596310 2. 14717231 3. 18989492 4. 28203412 This abstract is funded by: NA