Background Eagle's syndrome refers to a rare constellation of neuropathic and vascular occlusive symptoms caused by pathologic elongation or angulation of the styloid process and styloid chain. First described in 1652 by Italian surgeon Piertro Marchetti, the clinical syndrome was definitively outlined by Watt Eagle in the late 1940s and early 1950s. Methods This article reviews how underlying embryologic and anatomic pathology predicts clinical symptomatology, diagnosis, and ultimately treatment of the syndrome. Results The length and direction of the styloid process and styloid chain are highly variable. This variability leads to a wide range of relationships between the chain and the neurovascular elements of the neck, including cranial nerves 5, 7, 9, and 10 and the internal carotid artery. In the classic type of Eagle's syndrome, compressive cranial neuropathy most commonly leads to the sensation of a foreign body in the throat, odynophagia, and dysphagia. In the carotid type, compression over the internal carotid artery can cause pain in the parietal region of the skull or in the superior periorbital region, among other symptoms. Conclusions Careful recording of the history of the present illness and review of systems is crucial to the diagnosis of Eagle's syndrome. After the clinical examination, the optimal imaging modality for styloid process pathology is spiral CT of the neck and skull base. Surgical interventions are considered only after noninvasive therapies have failed, the two most common being intraoral and external resection of the styloid process.
Embryology and phylogenyThe embryologic history of the styloid process, stylohyoid ligament, and hyoid bone is a subject of debate. Revilla and Stuyt [69] suggest that the styloid process, stylohyoid ligament, and lesser cornu of the hyoid bone develop from endochondral ossification of Reichert's cartilage, the cartilaginous component of the second branchial arch. They assert that after 3 months of fetal life, Reichert's cartilage is disrupted and divided into five distinct components (from proximal to distal): tympanohyal, stylohyal, ceratohyal, hypohyal, and basyhyal [58,69]. The tympanohyal component contributes to the tympanic bone and the base of the styloid process. The stylohyal component contributes to the majority of the styloid process, and the hypohyal and basyhyal components contribute to the hyoid bone. In many animals the ceratohyal component ultimately becomes the epihyoid bone. In humans, Revilla and Stuyt [69] contend that it degenerates to form the stylohyoid ligament.In contrast, during their detailed description of Reichert's cartilage in 50 human embryos and fetuses, RodriguezVazquez et al. [72] suggested that the second branchial arch cartilage is formed in two distinct segments separated by mesenchymal tissue. The proximal and larger segment is continuous with the otic capsule and becomes the styloid process. The smaller and more distal component forms the
