[A retrospective study on anatomical morphological changes of pneumatized mastoid and sigmoid sinus bony wall in different types of sigmoid sinus dominance combined with high jugular bulb].

Objective

To investigate the anatomical correlation between sigmoid sinus dominance type and high jugular bulb（HJB）, and their interactive effects on sigmoid sinus morphology, jugular bulb morphology, and bone wall integrity, thereby providing anatomical evidence for preoperative imaging evaluation in lateral skull base and middle ear surgeries to reduce intraoperative injury risk.

Methods

A total of 288 patients with completely pneumatized mastoids who underwent temporal bone CT and CTA examinations at our hospital from August 2017 to March 2025 were consecutively enrolled. They were divided into nine groups based on sigmoid sinus dominance type（left/right/balanced） and jugular bulb position（low/middle/high）. Measurements included sigmoid sinus diameter, mastoid volume, bone wall thickness, jugular bulb bone wall thickness, area, and volume. Comparative analyses were performed on inter-group and intra-group differences in sigmoid sinus bone wall thickness and jugular bulb bone wall thickness; correlations between bone wall thickness of sigmoid sinus segments and jugular bulb; and distribution of bone wall integrity categories（normal, thinning, defect） across groups, using chi-square tests.

Results

Sigmoid sinus diameter was significantly enlarged on the dominant side（P<0.01）, with the largest left diameter in the left-dominant high-position group and the largest right diameter in the right-dominant high-position group. The balanced-horizontal high-position group exhibited the largest jugular bulb cross-sectional area and volume（P<0.05）. Mastoid volume showed no significant differences among groups（P>0.05）. No statistically significant differences in bone wall thickness of sigmoid sinus segments or jugular bulb were found across groups（P>0.05）, but significant positive correlations between sigmoid sinus segment bone wall thickness and jugular bulb bone wall thickness were observed in specific subgroups（P<0.05）. Jugular bulb integrity and its communication with air cells varied significantly among groups（P<0.01）, whereas sigmoid sinus bone wall integrity showed no inter-group differences（P>0.05）. The jugular bulb was the primary site of bone wall defects and abnormal communications.

Conclusion

Sigmoid sinus dominance type and jugular bulb position exhibit a coupled relationship, jointly influencing local vascular morphological features. High-positioned and enlarged jugular bulbs（particularly in the balanced-horizontal high-position group） are key risk factors for bone wall thinning, defects, and abnormal communications with air cells, while sigmoid sinus bone walls remain relatively stable. Preoperative CT imaging evaluation should integrate the anatomical relationship of both structures, with a focus on jugular bulb morphology and bone wall integrity, which is critical for preventing vascular injuries during lateral skull base and middle ear surgeries.