ANATOMICAL CONSIDERATIONS OF HIGH JUGULAR BULB IN LATERAL SKULL BASE SURGERY

In order to study high jugular bulb management in lateral skull base s urgery, an anatomical study was conducted on 30 temporal bones by exam ining the relationship between the internal auditory canal (IAC) and t he jugular bulb. The following parameters were measured: 1) Height of the jugular bulb (H) ... distance between the level of the jugular bul b dome and the line passing through the confluence of the sigmoid sinu s with the jugular bulb (SS-JB), 2) Mastoid length (ML)... distance be tween the mastoid process and middle cranial fossa dura, 3) Distance b etween the most inferior part of the porus acousticus and jugular bulb dome (A), 4) Distance between the porus acousticus and SS-JB (B). The jugular bulb was defined as high when it occupied more than two third s of (B). The incidence of a high jugular bulb was 23 per cent in this study. When the jugular bulb was high, the mean (H) and (A) were 9.4 +/- 1.9 mm and 2.7 +/- 0.5 mm, respectively. (H) was higher on the rig ht side than on the left side. No statistically significant difference was found between small and large mastoids (t-test: p>0.05). It was c oncluded that when a high jugular bulb was encountered during lateral skull base surgery, the jugular bulb position allows a very small work ing area inferior to the IAC. In these cases: a 3 or 4 mm depression o f the jugular bulb is necessary in order to expose the lower cranial n erves. This can be accomplished by lowering the jugular bulb with the technique already described.