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P078: CRANIOCERVICAL INSTABILITY AS A POTENTIAL DRIVER OF STYLOID PROCESS ELONGATION
Noritaka Sano; Yohei Mineharu; Etsuko Yamamoto-Hattori; Hiroyuki Ikeda; Shigeki Takada; Masahiro Tanji; Yoshiki Arakawa; Kyoto University

Background: The Styloid process is located inside the mastoid process and is attached to muscles such as the stylohyoid muscle. An elongation of 30 mm or more is considered excessive and can cause Eagle syndrome in some patients, typically in their 30s and 40s. However, the factors determining the length of the Styloid process have not been elucidated to date.

Materials and Methods: We studied a total of 83 patients under the age of 50 who were admitted to our hospital between 2010 and 2022, including those with head trauma (n=20), Chiari malformation (n=18), and non-functional pituitary neuroendocrine tumor (n=45). The main observation parameters were age, sex, average length of the Styloid process on both sides, and the clivo-axial angle (CXA) formed by the clivus and C2 odontoid process on sagittal images of plain CT scans.

Results: There was a positive correlation between age and the length of the styloid process (Spearman rank correlation coefficient 0.35, p=0.001), CXA was smaller in the Chiari malformation group at all ages. In 0-29 years old age group, CXA and the length of styloid process were not correlated, but there was a strong negative correlation at ages 30 years and older (Spearman's rank correlation coefficient -0.52, p<0.001).

Conclusion: Styloid process elongation occurs with age but is more likely to occur in Chiari malformations and patients with small CXA, which is associated with brainstem deformity and craniocervical instability.

Keyword: Chiari Malformation, Craniovertebral Junction Abnormalities, Clivo-Axial Angle, internal carotid artery, styloid process

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