USMLE Step 1 Question 313

Question:

A 15 year-old boy presents to your office complaining of a painful mass on the right side of his neck for one week. Last week he had a sore throat and productive, non-bloody cough that has since gone away. He has noticed that the mass usually becomes painful whenever he is sick with a sore throat, but it is never completely gone. He appears anxious because he cannot remember the last time the mass was not present. On physical exam, the mass is immobile and slightly painful to touch and his oropharynx exam is clear. What is the likely etiology of this patient’s mass?

Correct Answer: D.  Incomplete involution of branchial cleft three

This patient’s complaint is likely due to a branchial cleft cyst, due to an incomplete involution of branchial clefts two, three or four during the 7th week of embryonic development. Because they are lined with ectoderm, incomplete involution leaves behind an entrapped epithelium-lined cyst that may persist into adulthood, existing as a painless lateral neck mass only painful during infection. Answer choice A, bacterial abscess, would present with a more dire physical exam, perhaps draining pus, and a patient with febrile illness. Answer choice B, ectopic thyroid tissue, may be found at the base of the tongue or as part of a thyroglossal duct cyst, both of which are ruled out by normal physical exam. Incomplete involution of branchial cleft one, answer choice C, would lead to a disruption in the external auditory meatus, the normal derivative of cleft one, but would not result in a cyst. Neoplasm of the lymph nodes, answer choice E, is unlikely given the chronic nature of the cyst and the lack of other symptoms of lymphoma.