High jugular bulb: implications for posterior fossa neurotologic and cranial base surgery

The suboccipital-retrosigmoid approach to the internal auditory canal and cerebellopontine angle is being used with increasing frequency for neurotologic surgery, including vestibular nerve section and resection of acoustic neuroma. It offers wide exposure of the cerebellopontine angle and the cranial nerve VII-VIII complex as it courses from the brain stem to the temporal bone. Exposure of the internal auditory canal can be achieved by removing its posterior bony wall. Safe utilization of this approach requires familiarity with the variable position of structures within the petrous bone, including the lateral venous sinus and jugular bulb. We report here a case in which bleeding resulted from injury to a high jugular bulb during surgical exposure of the internal auditory canal via the suboccipital route and discuss the regional anatomy of the jugular bulb based on study of 378 consecutive temporal bone specimens from the collection of the Massachusetts Eye and Ear Infirmary. High jugular bulb was defined as encroachment of the dome of the bulb within 2 mm of the floor of the internal auditory canal. Forty-six percent of scoreable specimens met this criterion. However, when donors less than 6 years of age were excluded, a high jugular bulb was identified in 63% of specimens. Relevance to neurotologic surgery of the posterior fossa is presented.