Laser surface registration for lateral skull base surgery

Logistics in the run-up to computer-assisted lateral skull base intervention can be reduced by markerless registration methods. So far, only the facial skin surface but not the skin surface that was near to the lateral skull base was used for markerless patient registration. The present study was designed to evaluate whether the auricles may serve as an accurate spatial reference for markerless patient registration in image-guided lateral skull base surgery.

In a prospective clinical study, the precision of markerless patient registration was checked by using periauricular evaluation markers and additional distant oral evaluation markers that served as targets for the infrared pointer of a navigation system. Ten patients with cranial tumors, bony malformations, or foreign bodies who were planned for image-guided surgery were selected. Markerless patient registration was performed by laser-scanning with the SSN++ navigation system.

Based on the auricle, a high accuracy (mean target detection error tde = 0.9 mm +/- s = 0.3 mm) was achieved in markerless patient registration as long as the auricle was not deformed during CT imaging or during laser scanning. However, the conventional CT acquisition with a head support caused temporary auricular deformations in half of the patients, which made a precise laser-scan registration impossible.

Automated laser registration of the auricle reduces the logistical input in connection with computer-assisted lateral skull base surgery, ensuring the accuracy that has been achieved up to now with marker-based methods. Constantly good results can be achieved if the head support of the computer tomograph has an appropriate opening at the level of the auricles in order to avoid auricular deformations during CT acquisition.