Eagle syndrome: tissue characteristics and structure of the styloid process

Ruben D de Ruiter; Sanne Treurniet; Nathalie Bravenboer; Björn Busse; Jan Jaap Hendrickx; Jeroen C Jansen; Leander Dubois; Willem H Schreuder; Dimitra Micha; Bernd P Teunissen; Pieter G H M Raijmakers; Elisabeth M W Eekhoff; Felix N von Brackel

doi:10.1093/jbmrpl/ziae115

Eagle syndrome: tissue characteristics and structure of the styloid process

JBMR Plus. 2024 Aug 29;8(10):ziae115. doi: 10.1093/jbmrpl/ziae115. eCollection 2024 Oct.

Authors

Affiliations

¹ Department of Internal medicine, Endocrinology and Metabolism, Rare bone disease center, Amsterdam University Medical Centers, Vrije Universiteit, Amsterdam Movement Sciences, 1081 HV Amsterdam, The Netherlands.
² Bone and Calcium Metabolism Lab, Department of Clinical Chemistry, Amsterdam University Medical Centers, Vrije Universiteit, Amsterdam Movement Sciences, 1081 HV Amsterdam, The Netherlands.
³ Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, 22529 Hamburg, Germany.
⁴ Interdisciplinary Center for Interface Research (ICCIR), University Medical Center Hamburg-Eppendorf, 22529 Hamburg, Germany.
⁵ Department of Otolaryngology, Head and Neck Surgery, Amsterdam University Medical Centers, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands.
⁶ Department of Otolaryngology, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands.
⁷ Department of Oral and Maxillofacial Surgery, Amsterdam University Medical Centers, 1081 HV Amsterdam, The Netherlands.
⁸ Department of Human Genetics, Amsterdam University Medical Centers, Vrije Universiteit, 1081 HV Amsterdam Reproduction and Development, Amsterdam, The Netherlands.
⁹ Department of Radiology and Nuclear Medicine, Amsterdam University Medical Centers, 1081 HV Amsterdam, The Netherlands.

Abstract

Eagle syndrome is a bone disease where elongation of the styloid process leads to throat and neck pain, and in severe cases neurovascular symptoms such as syncope and neuralgia. The pathophysiology of Eagle syndrome is poorly understood with various theories having been proposed how this elongation is caused. To better understand the pathophysiology, we performed a work-up in 6 patients presenting with Eagle syndrome. Patients mainly presented with pain on turning the neck (100%), foreign body sensation (67%), tension in the neck (67%), and dysphagia (50%). The typical length of the styloid process ranges from 25 to 30 mm; however, [¹⁸F]NaF (sodium fluoride) PET/CT showed elongated styloid processes with an average length of 52.1 ± 15.6 mm (mean ± SD) with increased turnover at the base of one of the styloid processes. The removed styloid processes were further examined by histology, micro-CT, quantitative backscatter electron imaging (qBEI), Fourier transform infrared spectroscopy (FTIR), and circularly polarized light imaging. Histology revealed one case of a fractured styloid process healing through callus formation and one case of pseudarthrosis. Bone mineral density and mineralization was similar in the styloid processes when compared to cortical bone samples derived from the mandibular bone of different patients. Circular polarized light microscopy showed a collagen orientation in the styloid process comparable to the cortical bone samples with a distinct separation of collagen structure between the mineralized structure and the surrounding soft tissue with FTIR analysis demonstrating a typical composition of bone. This altogether suggests that the elongated styloid processes in Eagle syndrome are mature bone, capable of endochondral repair, possibly growing from the base of the process through endochondral ossification, rather than being a form of secondary calcification of the stylohyoid ligament as previously postulated.

Keywords: Eagle syndrome; [18F]NaF PET; bone QCT/μCT; bone histomorphometry; matrix mineralization.