<s>[INST] context: Brachial cyst Branchial fistula Develops from vestigial remnants of 2nd branchial cleft. Lined by squamous epithelium Contains thick, turbid fluid full of cholesterol crystals. Cyst usually presents in the upper neck in early or middle adulthood Found at the junction of upper third & middle third of the SCM muscle at its anterior border. Fluctuant swelling that may transilluminate and is often soft in its early stages USG and FNAC aid diagnosis. Treatment is by complete excision. Branchial fistula may be unilateral or bilateral Thought to represent a persistent 2nd branchial cleft Tract is lined by ciliated columnar epithelium There may be a small amount of recurrent mucous or mucopurulent discharger onto the neck External orifice is nearly always situated in the lower third of the neck near anterior border of SCM Internal orifice is located on the anterior aspect of posterior faucial pillar just behind the tonsil. Internal aspect of the tract may end blindly at or close to the lateral pharyngeal wall, constituting a sinus rather than a fistula. The tract follows the same path as a branchial cyst and requires complete excision often by more than one transverse incision in the ne [/INST] question: Most frequent site of branchial cyst is at: | options: A: Upper third of posterior border of sternocleidomastoid B: Lower third of anterior border of sternocleidomastoid C: Upper third of anteromedial border of sternocleidomastoid D: Supraclavicular fossa | answer: C </s>