Objective: Access to the floor of the middle cranial fossa (MCF) is often required for approaches to cranial base lesions. This study measures the craniocaudal distance between the zygomatic arch (ZA) and the floor of the MCF from a random sample of high-resolution computed tomography scans of the cranial base.
Methods: Forty computed tomography scans were imported into an OsiriX station and reconstructed in multiple planes. The most caudal point of the MCF was determined in each computed tomography scan. The distances between that point and the root of the zygoma and the middle point of the ZA were calculated. The thickness of the temporalis muscle and the vertical height of the zygoma were also calculated. A 2-tailed, paired Student t test was used to compare right and left measurements with a 95% confidence interval and P value <.05 as statistically significant.
Results: The foramen ovale was consistently the lowest point of the MCF. The average root-to-floor measurement was 5.05 +/- 0.42 mm above the floor of the MCF and distance of the mid-zygoma to the floor was 1.94 +/- 0.61 mm above the floor of MCF. The average temporalis muscle thickness and vertical height of the ZA were 22.22 +/- 0.36 mm and 8.10 +/- 0.13 mm, respectively. The muscle-to-floor measurement (muscle thickness + mid-zygoma-to-floor measurement) was 24.16 +/- 0.74 mm.
Conclusion: The routine use of a zygomatic osteotomy in approaches to the MCF does not provide very much increased exposure. However, in patients with exceptionally thick temporalis muscles or a high ZA, a zygomatic osteotomy may be helpful in providing exposure of the floor of the MCF.