A fluid-filled sac, bursa or cyst. A cystic hygroma is lined with endothelial cells derived from the lymphatic system.

Fluid-filled sac or cyst, most often caused by trauma.

a false bursa, which is a nonpainful, fluid-filled swelling surrounded by a thick, fibrous capsule that develops under the skin

a fluid-filled bursa which forms to protect the skin from pressure necrosis from the bone underneath

a fluid-filled cavity, encased by dense fibrous tissue, which develops under the skin on the side of one or both elbows

a fluid-filled growth that forms over boney regions due to repeated trauma

a localized fluid buildup usually in the subdural space