Anatomic limitations of posterior tympanotomy: what is the major radiologic determinant for the view field through posterior tympanotomy?

To radiologically evaluate the anatomic factors that may determine the view field or the accessibility of the posterior tympanotomy into the posterior mesotympanum, a cohort of 30 patients with pneumatic mastoids and 30 patients with unilateral sclerotic mastoids were included. Anatomic relationships were evaluated according to 5 parameters. The reference parameter of the view field through posterior tympanotomy was the maximum view to the stapes area through posterior tympanotomy. Direct distance between the chorda tympani nerve and the facial nerve (FN) and angle between the cortex of the external auditory canal and the FN showed significant positive correlations in pneumatic and sclerotic mastoids. However, the location of the FN was negatively correlated with the maximum view to the stapes area through posterior tympanotomy only in pneumatic mastoids. In particular, the angle between the cortex of the external auditory canal and the FN showed the best correlation with the maximum view to the stapes area through posterior tympanotomy. The angle between the cortex of the external auditory canal and the FN was the most important anatomic determinant for visibility through posterior tympanotomy. This study suggests that pneumatic mastoids, but not sclerotic mastoids, may have a more complex relationship including more factors than those considered in this study. Although this study was performed radiologically, this study can present the insight to surgeons or radiologists.