[A Case of Cystic Cervical Lymph Node Metastasis of HPV-positive Tonsil Cancer, Being Discriminated as the Branchiogenic Carcinoma].

In recent years, human papillomavirus (HPV)-positive oropharyngeal carcinomas have been increasing. The first manifestation of these tumors is frequently as cystic metastasis to cervical lymph nodes that may precede recognition of the primary tumor, so, they often result in misdiagnosis as branchial cleft cysts. We report a case of cystic cervical lymph node metastasis of HPV-positive tonsil cancer. The patient was a 70-years-old man who noticed a mass on his left neck. The tumor was large and soft, and it was diagnosed as benign in fine-needle aspiration cytology. We diagnosed the tumor as a branchial cleft cyst and undertook surgery. The histopathological diagnosis was squamous cell carcinoma arising from a branchiogenic cyst. However, because it did not satisfy the diagnostic criteria, we diagnosed the tumor as an unknown primary tumor. One year later, left tonsil cancer was suspected based on PET-CT imaging and a left tonsillectomy was undertaken, whereafter tonsil cancer was found. In p16 immunostaining, it was positive in both cystic mass and tonsil. The cervical mass was cystic lymph node metastasis of HPV-positive tonsil cancer. It is important to investigate the oropharynx, when we found cystic cervical mass, because HPV-positive oropharyngeal carcinoma frequently results in cystic neck metastasis.