Uncommon Presentation of Substernal Chylothorax Following Coronary Artery Bypass Grafting Without LIMA Harvest: An Atypical Case.

BACKGROUND Chylothorax is one of the rarest postoperative complications observed in patients undergoing coronary artery bypass grafting (CABG). Most reported cases of post-CABG chylothorax are associated with left internal mammary artery (LIMA) harvesting, which can injure the thoracic duct or its branches because of their close anatomical proximity. In contrast, the occurrence of chylothorax without LIMA grafting is extremely rare and can lead to diagnostic uncertainty. CASE REPORT We report the case of a 73-year-old man with triple vessel disease who underwent elective CABG via median sternotomy. LIMA was not harvested due to intraoperative hemodynamic instability, and revascularization was performed using venous grafts only. On the third postoperative day, substernal drainage of 200 to 300 mL per day with a purulent-like appearance was observed. Computed tomography (CT) demonstrated no abnormal fluid accumulation in the sternal region or thoracic cavity. Laboratory findings showed leukocytosis with lymphocyte predominance and low C-reactive protein levels, creating suspicion of infection but without clear confirmation. Surgical re-exploration revealed no infectious source. Subsequent pleural fluid analysis demonstrated markedly elevated triglyceride levels and the presence of chylomicrons, confirming the diagnosis of chylothorax. Conservative management was initiated, including chest drainage, total parenteral nutrition, and a low-fat diet. Drain output progressively decreased, and the patient was discharged after clinical improvement. CONCLUSIONS Substernal chylothorax following CABG without LIMA harvesting is an exceptionally rare presentation that can mimic postoperative infection. Early recognition, appropriate biochemical confirmation, and timely conservative management are essential to prevent complications. A structured diagnostic and management algorithm may help guide clinicians in similar cases.