Using a 3D Radiological Planning Software to Predict the Intraoperative Surgical View

A 3D radiological planning software for general otology has been developed to assist preoperative planning by providing anatomical measurements based on CT or MRI scans in cochlear implant candidates. This study aimed to investigate its usability for predicting the required posterior tympanotomy (PT) opening length to ensure visualization of the round window (RW).

CT scans were performed on 30 petrous bone specimens. Correlations were analyzed between software-calculated distances of the ideal trajectory to critical inner ear structures and the intraoperatively measured required PT length to ensure visualization of the RW. This was assessed using the posterior tympanotomy window (PTW), which was defined as the distance between the most prominent curvature of the short process of the incus and the round window. We also analyzed the degree of facial nerve exposure and the feasibility of electrode array insertion.

The mean PTW length was 7.31 mm (range, 5-9 mm). The intraoperative PTW significantly positively correlated with the distance between the chorda tympani and the ideal trajectory calculated by the software. The intraoperative PTW significantly positively correlated with the software-calculated facial recess size. A caudal extension of the PTW correlated with short distances between the facial nerve and the ideal trajectory. Facial nerve exposure negatively correlated with the software-calculated distance between the facial nerve and the ideal trajectory. Electrode insertion was possible in all study specimens.

The software was useful in the preoperative planning of CI surgery. It may help to anticipate the RW visualization through the chorda-facial angle.