A child is born with a branchial cyst presenting as a mass at the anterior border of the sternocleidomastoid muscle. Embryologically, which pharyngeal structure gives rise to the second branchial cleft cyst?
- A Remnant of the first pharyngeal cleft
- B Persistence of the thyroglossal duct
- C Persistence of the cervical sinus of His (fusion of the second arch over second, third, and fourth clefts) ✓
- D Failure of the second pharyngeal pouch to differentiate
Correct answer: C. Persistence of the cervical sinus of His (fusion of the second arch over second, third, and fourth clefts)
Explanation
During development, the second pharyngeal arch (of His) overgrows the second, third, and fourth clefts, burying them in the ectoderm-lined cervical sinus. Failure of the cervical sinus to obliterate results in a branchial (second cleft) cyst along the anterior border of the SCM, typically between the angle of the mandible and the clavicle. First cleft cysts appear near the ear; persistence of the second pharyngeal pouch would cause a tonsillar-related anomaly. Thyroglossal cysts are midline.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.