Radiologists Support Tricky Auditory Canal Surgery With 3-D Models

By Jennifer Allyn

Surgery on the inner auditory canal through the middle cranial fossa can be challenging due to the presence of several important anatomic structures in a confined space and the lack of consistent bony anatomic landmarks. Radiologists are assisting with this surgery by providing low-cost, high-precision 3-D printed models to help surgeons simulate the surgery beforehand.

Ghodadra

Stereolithography 3-D printing offers a means to create precise, patient-specific models of the temporal bones so surgeons can visualize and practice, according to Anish Ghodadra, MD, of Yale New Haven Hospital in New Haven, CT.

"The 3-D printed models of the lateral skull base enable otolaryngologists to have a better understanding of a given patient's anatomy and allow them to practice the surgical procedure prior to performing the actual surgery," Dr. Ghodadra said. "The models provide a realistic, patient-specific simulation of drilling of the bone in the skull."

To evaluate the effectiveness of the 3-D models, four cadaver heads were imaged with CT and the bony structures were segmented. 3-D meshes were prepared in modeling software with critical structures that the surgeons want to avoid injuring, such as the facial nerve and the membranous labyrinth, modeled as hollow cavities. These hollow cavities were filled with paint and sealed. If either structure was entered while drilling the model, the paint would leak and provide visual feedback to the surgeon.

Surgeons then practiced on the 3-D models, followed by the drilling of the corresponding cadaver head. Dr. Ghodadra and his team then measured the accuracy and utility of the model using visual analog scales.

Surgeons reported a median score of 95 out of 100 for the utility of the model in understanding the position of key underlying anatomy in relation to the surface anatomy. As a tool for training residents and fellows on lateral skull base surgery, the score also was 95 out of 100.

"Not only does a 3-D model help simulate this surgery, but it can also serve as a low-cost training tool for residents and fellows, giving them a better perspective of the inner auditory canal and its anatomic structures," Dr. Ghodadra said.

The development of the 3-D models can be time- and labor-intensive, according to Dr. Ghodadra, but should not deter surgeons from this type of pre-operative planning and training. The median time for segmentation of the anatomy and computer-aided design (CAD) modeling was three hours, while the print time was 7.7 hours. The material cost, however, was only $11 per model.

"Any surgery involving the skull in ENT could potentially benefit from these models. We have also created models for performing mastoidectomy and correction of external auditory canal atresia in the pediatric population," Dr. Ghodadra said. "When it comes to applications of these low-cost printing techniques, the sky's the limit."

The 3-D model of the inner auditory canal is finalized for training and the surgeon prepares to practice the procedure, avoiding the facial nerve and membranous labyrinth, which have been hollowed and filled with paint. If the areas are entered while drilling the model, the paint will provide a visual feedback to the surgeon.