Radiographic anatomy of the petrous apex: A study related to the middle fossa approach

Abstract

Objectives: The goal of our study is to use high resolution CT scanning to create standard measurements and ranges of commonly used anatomic landmarks for the middle cranial fossa approach. These measurements are then used to discuss the strengths and limitations of the systems currently used for IAC localization divised by House, Fisch, Garcia-Ibanez, Catalano, and others. Methods: High resolution CT images of the temporal bone 1.25 mm apart were obtained using the GE Lightspeed Ultra CT scanner. Identical head position was insured using the fixed landmarks of the hard palate (coronal plane) and anterior cranial fossa(axial plane). Scans were repeated if all images were not parallel to the anterior cranial fossa or perpendicular to the hard palate. All patients were 18 years of age or older; 108 temporal bones are included in the study. Films were read by a neurotologist and a neuroradiologist for evidence of abnormalities. Measurements were made using the standard PACS (picture archiving and communication system) measurement software. Results: Ten temporal bones had evidence of chronic otitis media and were thus excluded from the study. Pneumatization over the superior semicircular canal and IAC are recorded. In 78 temporal bones the superior semicircular canal was not the arcuate eminence. This mean distance was recoded. Likewise, angles and distances used by other studies are measured and discussed. Conclusion: Our study of 98 temporal bones provides the operator with ranges where important anatomic structures lie. These measurements allow the surgeon to safely and more rapidly locate the IAC when perfoming a middle fossa approach.