Abstract Introduction Chylothorax and urinothorax are rare, each representing under 1% of cases. Coexistence in single patient is exceedingly uncommon—fewer than ten such cases have been reported, typically in the context of trauma or retroperitoneal surgery rather than thoracic malignancy. This case illustrates an overlap of these two entities in advanced esophageal squamous cell carcinoma (SCC), raising questions about lymphatic disruption, obstructive uropathy, and the unintended consequences of thoracic duct embolization. Case Description 59-year-old woman with recurrent pleural effusion and locally invasive distal esophageal SCC. Pleural analysis from thoracentesis revealed triglycerides 279 mg/dL, cholesterol 27 mg/dL, and pleural amylase 26 U/L—consistent with a chylothorax. PET showed no discrete thoracic hypermetabolism, but the tumor abutted mediastinal structures, suggesting thoracic duct obstruction from regional invasion or radiation fibrosis. Given persistent chyle output despite dietary modification, she underwent two thoracic duct coil embolizations. After transient improvement, her chest tube output again increased to 1.5 L/day, with effluent becoming clearer rather than milky. Repeat fluid analysis revealed a pleural-fluid/serum creatinine ratio 1, consistent with concurrent urinothorax. This correlated with progressive urinary retention, bilateral hydronephrosis, and decreased urine output. In retrospect, the temporal relationship—emergence of high-output, low-lipid fluid following duct embolization—suggested that retroperitoneal lymphatic rerouting or diaphragmatic micro communications allowed urine to ascend into the pleural space once the primary lymphatic outflow was occluded. Given her functional decline, progressive cancer, severe protein-calorie malnutrition, and rising cholestatic liver injury from TPN, invasive diagnostic procedures were deferred as pt chose hospice. Discussion This case represents an extraordinarily rare coexistence of chylothorax and urinothorax, most likely due to a dual-pathway effusion mechanism: malignant or radiation-induced lymphatic obstruction producing chylous leakage, followed by retroperitoneal urinary translocation through collateral lymphatics after thoracic duct embolization. Previous case reports (Luo et al., Clin Respir J, 2020; Toubes et al., J Thorac Dis, 2017) describe similar dual effusions but almost exclusively following trauma, renal pathology, or urologic surgery—not thoracic malignancy. This patient’s course underscores several key lessons: In evolving pleural physiology after duct embolization, a mixed effusion mechanism should be considered when fluid characteristics or biochemistry change unexpectedly. PF/S creatinine ratio 1 remains a useful clue to urinothorax, even when coexisting with chylous components. In advanced malignancy, pursuing pathophysiologic clarity must be balanced against goals of care, as cure and comfort often diverge. This case expands our understanding of lymphatic-urinary cross-communication and highlights how therapeutic interventions may reveal—or create—rare physiologic conduits between seemingly separate systems. This abstract is funded by: None
Arif et al. (Fri,) studied this question.