Anatomical study of the superior jugular bulb by use of high-resolution computed tomography

Using high-resolution computed tomography, the relationship between the superior jugular bulb and the tympanic cavity was analysed in 40 subjects. Until now, the superior jugular bulb was thought to lie below the floor of the hypotympanum, however, the following observations were made from this study: 1) In 48 (60%) out of 80 temporal bones (40 cases), the top of the superior jugular bulb was situated in the higher level than the floor of the hypotympanum. 2) In 9 cases, the jugular bulb was separated from the tympanic cavity by only thin bony wall. This finding was noticed on the right side in 8 cases and was bilateral in a case. 3) In 21 cases (52.5%), the right jugular bulb was situated in higher level than the left, and the reverse finding was noticed only in 4 cases (10.0%). The reason why the right jugular bulb is frequently higher than the left was thought to be related to its function. Namely, the jugular bulb is useful to absorb the pulsation of the carotid artery, therefore, it was considered that the anatomical and physiological differences between the right and left carotid arteries induce the asymmetry of the jugular bulbs.