The prevalence of pneumatized articular eminence in the temporal bone. Do we need a high resolution computed tomography-based novel risk classification for eminectomy?

INTRODUCTION: Besides mastoid air filled cells, pneumatizations (PN) occasionally occur in the articular eminence (AE) of the temporomandibular joint (TMJ). These findings represent no pathological character but may increase the risk of perforating the AE during eminectomy with potential harming the skull base. Various classifications catagorize the degree of temporal PN without focussing solely on the AE. Panoramic radiograph (PR) and computed tomographie (CT) are both described as suitable for diagnosing PNs. Are the common ways of imaging capable for precise diagnosis and do we need a risk pattern for eminectomy?

METHODS: A 4-year retrospective study evaluated high resolution computed tomographie (HRCTs) of 300 patients. We screened digitalized skull images for PN of the AE. The frankfort horizontal was determined as the reference mark for measurements. Images were assessed by a craniomaxillofacial surgeon and a radiologist.

RESULTS: 300 patients (600 AEs) were investigated. We detected 60 PNs (10% of all AEs) in 44 patients (14.7%). We subdevided the findings according to the extent of PN. 10 AEs showed PNs of less than 20% (type 1); n=18: 21-40% (type 2); n=18: 41-70% (type 3). n=14: 71 to 100% (type 4). In 32 cases (72.7%) with 42 PNs a PR existed. Of the 42 AEs, corresponding PN could be detected in 21 cases (50%).

DISCUSSION: PNs are a potential threat when performing TMJ surgery. Sufficient preoperative imaging is required to avoid severe endangerment for the patient. CT imaging is most suitable detecting PNs. PR seem to fail in diagnosing PNs of different degree. Our novel HRCT-based classification shows the distribution of PNs and provides a risk pattern.

CONCLUSION: HRCT exceeds the diagnostic accuracy of PR in detecting pneumatized AEs. PR is not capable for detecting PNs of different degree. A novel classification may increase the prediction of perforation risk. Restricting eminectomy to reduce height only to a certain amount reduces the risk of complications.