[The NEN (Nicolet Electronic Naviation System) ENT navigation system. Initial clinical application]

Intraoperative computer navigation will soon play an important role in procedures performed on the anterior and lateral skull base. Electromagnetic systems compared to optical systems offer some advantages such as small hardware dimension and free unimpaired mobility of the surgeon.

The NEN navigational system (Nicolet Electromagnetic Navigation System) was used in 22 patients who underwent microscopic/endoscopic surgery for polypoid rhinosinusitis. It is the prototype of a new system, which localizes the surgical probe via the measurement of pulsed electromagnetic DC fields. This system was modified for the needs of head and neck surgery. Preoperative imaging data consisted of an axially oriented spiral computed tomography (CT) resulting in a slice thickness of 1 mm with a radiation dose slightly higher than a routine coronary CT scan of the paranasal sinuses.

The data acquired during clinical application was used to optimize navigation accuracy. The number and positions of the markers were gradually modified and improved. Six markers including the volume of the paranasal sinus system (three non-coplanar frontal markers, one on each of the mastoid processes and one median marker on parietooccipital junction) offered the best navigation precision. Additionally, all surgical instruments measured as ferromagnetic, i.e., nasal specula, were replaced by titanium instruments. An adapter affixed to the maxilla-designed to hold a second sensor used to track the patient's head was developed. With these modifications, it was possible to improve navigation accuracy to 1.5 mm in the plane of the sphenoid bone while retaining free head movement of the patient.

For routine procedures such as microscopic/endoscopic endonasal sinus surgery, the systems have to be cost effective and easy to operate.