A Thermal Injury Alarm System in the Expanded Endonasal Approach to the Skull Base

Expanded endoscopic endonasal approaches to the skull base allow the surgeon to access and remove benign and malignant tumors of the ventral and ventral lateral skull base. The procedure utilizes the natural nasal corridors and avoids incisions on the head and face. This technique often includes drilling the bone that surrounds the optic nerve, cavernous sinus, and branches of the trigeminal nerve to expose the pathology. Due to the nature of the shallow, confined space in the skull, the ability to cool the burr tip is limited and high temperature exists at the bone-burr interface. Thermal injury from drilling adjacent to these nerves is of particular concern because neurosurgeons have no way to gauge the tissue temperature. This research aims to develop a system to provide surgeons real-time temperature feedback at critical nerves during the surgery.

The electrical power generated by the drill console is the key information because it drives the drill motor to maintain a certain rotation speed. Changes in drill power are nearly proportional to changes in temperature at the bone-burr interface. As in many cutting processes, approximately 99% of the energy consumption converts into heat, and part of the heat flows into the bone and propagates to the surrounding tissues. Through a statistically designed experimental study, the conversion model of power-to-heat generated can be created. Preliminary results have demonstrated this approach in an ex vivo bone drilling setup.

Having known the heat generation on the burr-bone interface, a bio-heat transfer model can be applied to calculate the temperature response around the drilling site. The model is established from patients' preoperative CT and MRI data with the exact anatomic shape of bone and nerve, and the burr location is tracked via the intraoperative navigation system. This thermal analysis module will be able to provide a real-time thermal map onto the patient 2-D CT images. Surgeons can select CT images of interest to view the drilling temperature simultaneously. This system is expected to dramatically improve the quality of life in patients suffering from skull base tumors.