Hygroma is a medical term referring to a fluid-filled sac that develops under the skin. There are several synonyms used to describe this condition, including ganglion cyst, synovial cyst, and cystic hygroma. Ganglion cyst is the most common synonym used for hygroma, and it typically occurs in the wrist or hand. Synovial cysts, on the other hand, are typically found in the spine. Cystic hygromas are another form of hygroma that typically occurs in infants. Other synonyms for hygroma include bursitis, adventitial bursitis, and adventitial cystic disease. Regardless of the synonym used, treating hygromas usually involves draining the fluid and relieving pressure on the affected area.