Introduction: Many previous studies of high jugular bulb (HJB) have limitations, such as focusing simply on the incidence or having a relatively small number of subjects. The objective of this article was to investigate the overall incidence of HJB and bony dehiscence in HJB on a large scale using high-resolution temporal bone computed tomography. The other purpose was to measure the horizontal distance from the tympanic annulus and the height above the annulus. The next step was to classify HJBs according to relative levels compared with surrounding structures.
Materials and methods: Temporal bone computed tomographic images from January 2005 to April 2010 at Pusan National University Hospital, a tertiary care center, were reviewed retrospectively. Exclusion criteria were patients younger than 10 years, a previously operated ear, cholesteatoma with bony destruction, adhesive otitis media with unclear position of tympanic membrane, and congenital anomalies of the ear. We investigated the incidence of HJB, the bony dehiscence of the HJB, horizontal distance, vertical height of HJB, and classified HJB in relation to neighboring structures. We used the cochlear basal turn and the lateral semicircular canal as criteria for classification because they were readily seen in most cases: group A, above the inferior bony annulus of the tympanic membrane and below the cochlear basal turn; group B, above the cochlear basal turn and below the lateral semicircular canal; and group C, above the lateral semicircular canal.
Results: Total 2,299 cases (4,598 ears) were finally examined. The study group consisted of 1025 male and 1,274 female patients, aged 11 to 90 years (mean, 48.0 yr). Of the 2,299 patients, 298 (13.0%) had HJB. HJB was observed in 435 (9.5%) of 4598 ears. HJB was more prominent on the right (right:left = 1.88:1; p < 0.01). Of the 435 HJB cases, 121 (27.8%) had bony dehiscence. HJB with bony dehiscence also was more prominent on the right (right:left = 2.03:1; p < 0.01). The average horizontal distance between HJB and the inferior bony annulus of the tympanic membrane was 2.2 ± 1.8 mm. HJB in contact with the tympanic membrane was seen in 47 ears (47/435, 10.8%). The average vertical height between the HJB and the inferior bony annulus of the tympanic membrane was 59.1 ± 27.4 mm. In the classification, group B was most common (62.1%).
Conclusion: A meaningful proportion of HJB ears had bony dehiscence contact with the tympanic membrane. In planning ear surgery and other interventions, physicians should keep in mind the possibility of HJB and its bony dehiscence, which can lead to inadvertent injuries.