At 10 days of age, complete excision histology confirmed a benign, macrocystic lymphatic malformation lymphangioma ( commonly known as cystic hygroma or cystic lymphangioma).

These lesions commonly occur in the neck and axillae, with a minority of cases involving the neck and mediastinum. Differential diagnosis would include the broad categories of anterior and post cervical/thoracic mass lesions and would include cervical/mediastinal teratoma, cervical meningocele, occipital encephalocele, thymic masses, and neurogenic tumors.