Design of Physical Surgical Simulator for Drilling in the Expanded Endonasal Approach to the Skull Base

Drilling of the anterior skull base via the expanded endoscopic endonasal approach is a delicate and complex neurosurgical procedure that may result in mechanical and thermal injuries to adjacent cranial nerves, arteries, venous structures, dura mater, and brain parenchyma. Patients suffering from malignancies of the anterior skull base often require radical surgical resection of the tumor. High-speed drills mounted with miniature diamond burs are typically used to remove the bone to provide exposure for tumor resection. This procedure often includes drilling the bone encasing the optic nerves, cavernous sinuses, internal carotid arteries, and branches of the trigeminal nerve. Two of the most feared complications of this surgical approach are (1) thermal or mechanical injuries to cranial nerves from drilling, and (2) stroke caused by coagulation of blood in the internal carotid arteries because surgeons cannot ascertain the tissue temperature or control the extent of thermal injury during the bone drilling. What is more, this procedure is now commonly performed endoscopically, for which visualization requires skillful manipulation of the endoscope, rather than the open visualization to which surgeons are accustomed. Currently, there is no existing physical anterior skull base simulator available for training and practice. A commercially available virtual reality simulator provides clear visualization, but the haptic feedback for drilling is lacking. Trainees still must practice drilling on cadavers and patients. To provide a better and more accessible training environment, we have developed a low-cost, practical surgical simulator specifically for drilling in the expanded endonasal approach.

This simulator features a replaceable insert for drilling, a soft nasal tissue mask, and nerves and arteries with temperature sensors. The insert is built from high-resolution computed tomography and magnetic resonance images of an anonymous patient, and 3-D printing technology. The insert includes important anatomic features, such as a pituitary prominence, carotid prominences, and opticocarotid recesses, which serve as landmarks within the sphenoid sinus to identify the positions of nerves, arteries, veins, and brain structures. In addition, the insert is made of epoxy-treated plaster, formulated to provide haptic feedback similar to intraoperative drilling of bi-cortical cranial bone. This soft mask includes the nasal septum, turbinates, and skin to mimic the constraints to drill movement inherent in endonasal drilling. The silicone material (Dragon Skin), which is commonly used to simulate skin, is adopted for the mask using a plastic mold created using 3-D anatomic images. The optic nerve and internal carotid artery are also molded based on their anatomic shapes, with thermocouples embedded to measure surface temperature changes induced by heat transferred from adjacent bone. The temperature reading is corrected in post processing using an algorithm accommodating the differences in thermal properties between plaster and cranial bone.

The prototype of this surgical simulator has been tested in terms of feasibility and ease of use, using operating room equipment, by both neurosurgery faculty and residents. The aim of this study is to refine this simulator to serve as a training tool for residents learning the expanded endonasal endoscopic approach.