Misleading Mediastinal Fluid Collection: A Rare Presentation of Chylothorax

We report the case of a 68-year-old man presenting with rapidly progressive left cervical swelling, sialorrhea, and dysphagia. Imaging revealed a cervical fluid collection extending into the anterior mediastinum, initially suggestive of descending mediastinitis. Broad-spectrum antibiotic therapy was initiated, and surgical drainage was planned. Intraoperative exploration, however, revealed opalescent, milky fluid consistent with chyle, leading to a revised diagnosis of spontaneous chylocervical collection associated with chylothorax. Cultures were negative, and biochemical analysis confirmed markedly elevated triglyceride levels. Conservative management with total parenteral nutrition and a nil per os regimen achieved rapid resolution. Lymphangiography demonstrated normal thoracic duct anatomy without leakage. The patient was discharged in good condition, and follow-up imaging showed complete recovery. This case highlights the diagnostic challenge of differentiating chylous from infectious mediastinal collections, particularly when clinical presentation mimics descending mediastinitis. Accurate intraoperative assessment and multidisciplinary management are essential to avoid unnecessary invasive procedures. Rare etiologies such as idiopathic chylothorax should be considered in atypical presentations of cervical and mediastinal fluid collections.