The styloid process and the formation of sigmoid sinus diverticulum: is there a link?

INTRODUCTION: Sigmoid sinus diverticulum has been considered the most common cause of pulsatile tinnitus; the mechanism underlying sigmoid sinus diverticulum formation is unclear. To the best of our knowledge, no previous studies have assessed whether the formation of sigmoid sinus diverticulum is related to compression of the internal jugular vein by the styloid process. OBJECTIVE: To discuss the relationship between the styloid process and the formation of sigmoid sinus diverticulum. METHODS: The medical records of nine patients diagnosed with venous pulsatile tinnitus caused by sigmoid sinus diverticulum were reviewed between April 2009 and May 2019. All patients underwent high-resolution computed tomography of the temporal bones, computed tomography venogram of the head and neck, magnetic resonance venography, and brain magnetic resonance imaging. The length and medial angulation of the styloid process were measured, and compression of the internal jugular vein was recorded. RESULTS: The study population consisted of nine female right-sided pulsatile tinnitus patients with a mean age of 53.8 ± 4.6 years. The mean lengths of the styloid process were 3.9 ± 0.6 cm on the right side and 4.1 ± 0.7 cm on the left side. The mean medial angulation of the styloid process was significantly smaller on the right side than the left side (65.3° ± 1.2° vs. 67.8° ± 1.7°, p < 0.05). In addition, computed tomography venogram of the head and neck demonstrated the left internal jugular vein was compressed by the styloid process in eight of the nine patients. CONCLUSION: The formation of sigmoid sinus diverticulum with venous pulsatile tinnitus may be related to compression of the contralateral internal jugular vein by the styloid process. However, accumulation of data in additional cases is required to verify this suggestion.