Solitary cystic metastatic lymph node of occult human papillomavirus-related oropharyngeal cancer mimicking second branchial cleft cyst: A case report.

RATIONALE: Human papillomavirus (HPV)-related oropharyngeal cancer is becoming more common, the primary cancer AQ4 usually occult and appearing only as cystic cervical lymph node (LN) metastasis. Distinguishing between a benign cystic lesion and cystic LN metastasis is challenging given their similar radiologic and histologic appearances. PATIENT CONCERNS: A 54-year-old man presented with a bulging cystic mass measuring 6.4cm on the right side of neck. DIAGNOSES: Postexcision diagnosis was second branchial cleft cyst. After 2 years, the cystic mass recurred, and HPV-related tonsillar squamous cell carcinoma with cystic metastatic LNs was confirmed after wide tonsillectomy and neck dissection. The previous cystic lesion proved to be a cystic metastatic LN from the same malignancy with additional p16 immunostain. INTERVENTIONS: The patient was treated with adjuvant concurrent chemoradiation therapy. OUTCOMES: The patient was followed up in the outpatient department with no evidence of recurrence after 1 year. LESSONS: When an adult has a cystic mass in the upper neck, we must rigorously exclude it as a cystic metastatic LN of occult HPV-related oropharyngeal cancer. Additional p16 staining might be helpful.