Histological Investigation on Enlarged Styloid Processes and Ossified Stylohyoid Ligaments in Patients with Eagle Syndrome

Abstract

Objective: The Eagle syndrome is a rare condition. The highly heterogeneous symptom complex arises from an elongated styloid process or an ossified stylohyoid ligament. The causes of the pathological ossification processes are not fully understood. This study aimed to investigate the histological structure of enlarged styloid processes (SP) and ossified stylohyoid ligaments (SHL) in Eagle syndrome patients to understand their etiology and formation processes. Methods: A 2-year retrospective study was conducted, analyzing bone samples from 22 Eagle syndrome patients diagnosed with either type I (enlarged SP) or type II (ossified SHL). Imaging, surgical planning, and histological investigations were performed to characterize the bone structures. Histological analysis focused on bone structure, bone apposition, styloid tips and ligaments, and intraosseous cartilage remnants. Covariates included patient demographics, surgical procedures, and anatomical variations observed during histological examination. Microscopic analyses were conducted on tissue samples using various staining techniques to evaluate bone structure, cartilage remnants, and signs of ossification. Results: Histological examination revealed lamellar bone in both type I and type II cases, with differences observed in bone apposition and cartilage remnants. Subperiosteal bone apposition was more pronounced in type I cases, while cartilage remnants with enchondral ossification were found in both types. Conclusion: Eagle syndrome comprises distinct types characterized by either enlarged SP or ossified SHL. Histological findings suggest that both types involve osteogenesis from fibrous cartilage tissues and cartilage remnants, contributing to bone tissue growth. Understanding these processes is crucial for effective diagnosis and management of Eagle syndrome.