Abstract
Congenital thoracic lymphovenous aneurysms are exceedingly rare. They often present with compressive symptoms or thrombosis, necessitating surgical excision for symptom relief and cosmetic reasons. We report a symptomatic subclavian vein aneurysm in a 4-month-old infant who presented with a rapidly enlarging axillary mass. Multimodal imaging with ultrasound, computed tomography, and magnetic resonance imaging confirmed the diagnosis of subclavian vein aneurysm. The patient underwent surgical resection, and histology confirmed a lymphovenous malformation. Postoperative recovery remained uneventful aside from a chylothorax. On early follow-up at 15 months, the child remained well with no recurrence or residual symptoms.