Answer: b) 2nd Branchial cleft cyst (SABISTON 19th ED, P-814)Ectopic thyroid and Sternomastoid tumor does not become larger and tender during upper respiratory infectionsSternomastoid tumor is situated within sternocleidomastoid muscle and usually presents in early infancy, usually at 2-3 weeks of life.MCC of cervical adenopathy is viral URl. The associated lymphadenopathy generally subsides within 2 weeks, although mononucleosis-related lymphadenopathy may persist for 4 to 6 weeks. Also, clinical history and imaging picture does not favour lymphadenopathyNonlymphoid masses anterior to the sternocleidomastoid muscle are usually branchial cleft cystsBRANCHIAL CLEFT CYSTSFirst branchial cleft cysts develop in the preauricular or submandibular area, are intimately associated with the external auditory canal and parotid glandSecond branchial cleft cyst is the most common typeSecond and third branchial cleft cysts and tracts develop anterior to the sternocleidomastoid muscle and often become symptomatic after upper respiratory tract infections.Although the second branchial cleft communicates with the ipsilateral tonsillar fossa, the third communicates with the piriform sinus.Second branchial cleft tracts course between the internal and external carotid arteries.Third branchial cleft tracts course posterior to both branches of the carotid artery