The clinical case of a 60 year old female is reported who, incidentally, had the diagnosis of a retropharyngeal tumor, causing the anterior dislocation of the right tonsil. Imagiological studies (CT and NMR scans) were compatible with the diagnosis of "neurogenic tumor" or "vagal paraganglioma" and an attempt to a biopsy was failed, having collected only blood. An angio-RM allowed the definitive diagnosis of a large sacular aneurysm of the internal carotid artery, of unknown etiology. The patient underwent surgical management, consisting in the resection of the aneurysm and re-establishment of the arterial continuity by end-to-end anastomosis. Pathological studies of the specimen revealed an unsuspected traumatic etiology, probably related to a violent cervical blunt trauma occured several years before. The main features of the pathogenesis, topography, clinical manifestations and treatment of this condition are discussed, based on the most recent data published in the literature.