A 17-year-old boy presents to the clinic with a painless, slow-growing swelling on the left side of his neck. He reports that the mass has been present for several years but recently became enlarged and tender following an upper respiratory infection. Past medical history is otherwise negative. Vital signs are within normal limits. On physical examination, there is a 3-cm, soft, fluctuant, non-tender mass located at the anterior border of the upper third of the left sternocleidomastoid muscle, just below the angle of the mandible. The mass does not move with swallowing or tongue protrusion. There are no skin openings or drainage.
Which of the following is the most likely diagnosis?
The correct answer is:
A) Branchial cleft cyst
A branchial cleft cyst is a congenital epithelial cyst that arises from the failure of the second branchial cleft to involute during embryonic development. While they are present at birth, they often remain asymptomatic until late childhood or early adulthood, when they frequently enlarge or become infected following a viral illness. The classic presentation is a lateral neck mass, typically located anterior to the sternocleidomastoid muscle and near the angle of the mandible. Unlike thyroglossal duct cysts, they are not midline and do not move with tongue protrusion.
Answer choice B: Cystic hygroma, is incorrect. These are congenital lymphatic malformations that are usually diagnosed at birth or in early infancy. They typically present as a large, soft, transilluminating massein the posterior triangle of the neck.
Answer choice C: Laryngocele, is incorrect. This is a dilation of the laryngeal saccule. While it can present as a neck mass, it is typically associated with musicians who play wind instruments or glassblowers, and they change in size with the Valsalva maneuver.
Answer choice D: Thyroglossal duct cyst, is incorrect. These are located in the midline of the neck and move upward with tongue protrusion or swallowing.
Answer choice E: Zenker diverticulum, is incorrect. Zenker diverticulum is an out-pouching of the posterior pharyngeal wall. It typically presents in older adults with dysphagia, regurgitation of undigested food, and halitosis.
Key Learning Point
Branchial cleft cysts (specifically the second cleft, which accounts for 95% of cases) are the most common cause of a congenital lateral neck mass. They are located anterior to the sternocleidomastoid muscle. Diagnosis is often made clinically but can be confirmed with ultrasound or CT. Treatment is surgical excision to prevent recurrent infections.
