[Malignant branchiogenic cyst--fact or fiction?].

A case of a cystic metastasis of squamous cell carcinoma of palatine tonsil in a 54-year-old male is reported, clinically presenting as a branchiogenic cyst. The grade of differentiation of the squamous cell epithelium lining the cyst was very variable: in some areas it was extremely well differentiated, thus resembling common benign branchial cleft cyst; transition to dysplastic areas with features of carcinoma in situ was visible and finally, in one small focus, invasion of the epithelial structures into the lymphoid tissue was observed. Despite its metastatic nature, the tumor fulfilled histological criteria of a so called malignant branchiogenic cyst (branchiogenic carcinoma). The authors discuss the existence of primary malignant branchiogenic cyst and the criteria necessary for its diagnosis.