Morphological and positional relationships between the sigmoid sinus and the jugular bulb.

The purpose of this study was to determine the quantitative relationships between the positions of the sigmoid sinus (SS) and jugular bulb (JB) and the influence of mastoid pneumatization upon these structures. The investigations were carried out on 116 healthy adult ears based on the axial images of computed tomography (CT). The reference system locating the displacements of the SS and JB was established and the shape and position of the SS and JB were measured. The volume of pneumatization was quantitatively measured based on the serial digital images of CT. The method of partial correlation analysis was used to find the real relationship of two variables from the complicated dependence relationships. There was a tendency for the SS in the males to be situated more laterally and more backwardly, and the JB in the males was situated more laterally with thicker lateral bone wall when compared to the females. When compared to the left side, the SS on the right side tended to protrude more deeply and was situated more laterally and with less thickness of the lateral bone wall. In male, the right SS was situated more anteriorly than the left SS. In female, the right JB was situated more posteriorly than the left JB. There was a tendency for the SS to be situated more medially, to have a thicker lateral bone wall, and to protrude more superficially in the well-pneumatized bones. When the pneumatization was well, the JB tended to be situated more backwards and have a thicker lateral bone wall. However, there was no significant difference of pneumatization between the high JB group and the low JB group. The SS position and JB position changed synchronously in forward-backward or medial-lateral directions. The results suggest that the factors that influence the shape and position of the SS and JB are multiple. The results suggest that the morphological and positional relationships between the SS and the JB are complicated but could be grasped. The development of the cranial base, the temporal bone pneumatization and non-synchronous dural venous development between the right and left sides are considered to contribute to the morphological and positional changes of the SS and JB.