False about the swelling is:

B i.e. Filled with bloodRef: Bailey and Love, 27th edition, page 754-755Explanation:CYSTIC HYGROMANew terminology for cystic hygroma is Cavernous Lymphangioma.It is formed during embryological development of lymphatic system, when any of the jugular lymph sacs gets sequestered to develop into a lymphatic cyst.Most common site is posterior triangle of neck*, followed by axilla, retroperitoneum, cheek, mediastinum and groin.It presents at birth with a huge cyst in the neck leading to obstructed labour.It is very large, smooth, cystic, fluctuant, brilliant transilluminant swelling which is not reducible.It is filled with clear lymph with lining epithelium.It attains very large size, to cause respiratory insufficiency and stridor.It is multiloculated, can get infected often, or can cause lymph ooze.Treatment is difficult surgically, as it involves several anatomical planes and cannot be excised completely.Sclerosant injection with OKT32 or Picibanil is gained popularity.