Ultrasound shows a cystic hygroma in chest. what does this mean?

Lymphatic spaces: Cystic hygroma is cavernous lymphatic spaces that communicate and grow to form large cysts that can infiltrate the surrounding tissue. Cystic hygromas can be discovered before birth or ineonatal period. Occasionally, the cystic hygroma may not be discovered until the patient is older. There are now chemical therapies where medication placed in multiple cystic areas to decrease size of lesion.