Branchial Cleft Cyst
While a baby is developing in the womb, the neck and face form from five basic building blocks called the branchial arches. Each arch is separated by a groove or cleft. A persistence of this cleft with an opening to the outside (or inside) of the neck is called a sinus tract. If this cleft persists with no communication to the outside or inside of the neck, it may fill with fluid, resulting in a branchial cleft cyst. A child may can have both a sinus tract and cyst.

Sinus tracts with an external opening to the outside are often noted at birth or soon thereafter. Such tracts may be completely asymptomatic or drain fluid of variable consistency and quantity.

Branchial cleft cysts typically present in childhood but can occur at any age. An asymptomatic mass on either the left or right side of the neck anywhere from the jaw to the clavicles is most common. Sometimes the fluid in the cyst can become infected, resulting in the sudden appearance of a tender neck mass.