[Fourth branchial cyst within the thyrohyoid membrane: a difficult differential diagnosis with mixed laryngocele].

We present a case of a 62-year-old female patient with a right latero-cervical mass and an enlarged arytenoepiglottic fold, that caused voice disturbances. Computed tomography of the neck depicted an unilocular and homogeneous well-defined cyst located in the right parapharyngeal space that extended through the thyrohyoid membrane. It was initially diagnosed of mixed laryngocele. During surgical resection, no connexion between the lesion and laryngeal ventricle was detected, so the final diagnosis was branchial cyst. We discuss the pathogenicity and clinical, radiological and histological findings that facilitate differential diagnosis between mixed laryngocele and branchial cysts, mainly those derived from the second and fourth clefts. The radiological and histological findings in both lesions may be similar, so only the communication with the larynx, or its absence, can solve diagnostic doubts, course.