Helical CT and its three-dimensional image: Application for image-guided surgery in middle cranial fossa approach

Three-dimensional image for the middle fossa approach and its anatomical considerations

OBJECTIVE

To investigate the usefulness and significance of three-dimensional images in the middle cranial fossa approach.

STUDY DESIGN

Retrospective study.

METHOD

Three-dimensional images of 12 patients with acoustic neuromas were made for surgical guidance. An image showing an ideal surgical view was prepared, which showed no overlap between the labyrinthine bone and internal auditory canal (IAC) with a slight gap between them. The IAC was located and opened referring to this image.

RESULTS

Directions of the images in the ideal surgical view were anterior from lateral position in all cases. Viewing toward the vestibule, angle from lateral plane was 24 degrees +/- 12 degrees (mean +/- standard deviation). In 11 of 12 patients, the IAC was safely opened; in one patient the IAC could not be opened because of bleeding. Overall hearing preservation rate was 82%.

CONCLUSION

Our method facilitated not only in the identification of the IAC but also in avoiding inner ear damage. Our data indicated that the center of craniotomy should be made anterior to the external auditory canal and surgery should be viewed from an anterolateral position for a safe procedure.

Three-dimensional imaging of the internal auditory canal in patients with acoustic neuroma

Three-dimensional imaging of the internal auditory canal (IAC) was carried out in 21 patients with acoustic neuromas using helical computed tomography. The IAC was widened in 20 patients, but no irregularities of the canal walls were seen. In addition, the shape of the enlarged IAC corresponded to that of the tumor on magnetic resonance imaging. The data suggest that widening of the IAC in acoustic neuroma patients is due to enlargement of the tumor. Other mechanisms, for example, tumor invasion or destruction caused by release of a specific mediator from the tumor, are unlikely to explain these findings; however, further investigation is needed.