Spontaneous retropharyngeal and mediastinal thoracic duct cyst in an infant with respiratory distress

Thoracic duct cysts (TDC) within the retropharyngeal space and mediastinum are exceedingly rare lesions, with the majority related to trauma or neoplasm. We describe a case of an otherwise healthy 8-month-old boy who presented with severe respiratory distress, which was found to be caused by a large, spontaneous TDC occupying most the retropharyngeal and mediastinal space. To our knowledge, this is the youngest patient to date presenting with TDC. Ultimately, his TDC was completely resolved with sclerotherapy, however the patient's age and size presented unique challenges to his medical management, which we describe below.