All of the following statements regarding branchial cysts are true except

.BRANCHIAL CYST It arises from the remnants of second branchial cleft. Normally 2nd, 3rd, 4th clefts disappear to form a smooth neck. Persistent 2nd cleft is called as cervical sinus which eventually gets sequestered to form branchial cyst. Features * Swelling in the neck beneath the anterior border of upper third of the sternomastoid muscle. It is smooth, soft, fluctuant, often transilluminant with a sensation of 'Half-filled double hot water bottle'. ref:SRB&;s manual of surgery,ed 3,pg no 381