The Syndrome of Elongated Styloid Process, the Eagle's Syndrome-From Anatomical, Evolutionary and Embryological Backgrounds to 3D Printing and Personalized Surgery Planning. Report of Five Cases

Background and Objectives: The symptoms of Eagle's syndrome are associated with the elongated styloid process of the temporal bone or calcification of the stylohyoid ligament. The first mention of pain syndrome associated with the elongated styloid process dates back to 1937, when it was described by Watt Weems Eagle. Over the last decade, experts in the field have shown a lively interest in the issue of the relationship between the elongated styloid process and various symptoms. This article presents the correlation between the clinical signs of Eagle's syndrome and alterations in surrounding anatomical structures. It includes a brief review of the evolutionary, embryological and clinical anatomical background of the elongated styloid process. Materials and Methods: Between 2018 and 2019, five patients were admitted to our workplace with 1-3-year history of bilateral or unilateral throat pain, otalgia and pharyngeal foreign body sensation. As a therapeutic novelty in the surgical approach to this condition, we used individual 3D printed models to measure and identify the exact location of the resection of the styloid process without damaging the surrounding anatomical structures, such as the facial, accessory, hypoglossal, and vagal nerves; the internal jugular vein; and the internal carotid artery. Results: Compared to traditional surgical methods without 3D models, 3D models helped to better identify cutting edges and major landmarks used in surgical treatment of Eagle's syndrome. Printed models provided assistance with the exact location of the styloid process resection position without damaging the surrounding anatomical structures such as the facial, accessory, hypoglossal, and vagal nerves; the internal jugular vein; and the internal carotid artery. Conclusion: In our clinical report, we used 3D printed models for navigation and planning during surgical procedures involving resections of the elongated styloid process. Additionally, we can formulate a new hypothesis: the elongated styloid process is a form of atavism of the bony hyoid apparatus in our evolutionary ancestors that is evolutionarily encoded or arises from disrupted degeneration of the middle portion of embryonal Reichert´s cartilage of the second pharyngeal arch. Under normal conditions, this portion does not ossify but degenerates and transforms into a connective tissue band, the future stylohyoid ligament.

Keywords: 3D printing; Eagle’s syndrome; clinical anatomy; elongated styloid process; embryological development; evolutionary history.