On ``Evaluation of the Contribution of CAS in Combination with the Subcranial/Subfrontal Approach in Anterior Skull Base Surgery'' (Skull Base 2001;11:59-76)

Laedrach et al. recently published a study on the usefulness of navigation technology in anterior skull base surgery (Evaluation of the contribution of CAS in combination with the subcranial/subfrontal approach in anterior skull base surgery. Skull Base 2001;11:59-76). The authors presented 31 cases of various pathologies, including 6 mucoceles treated through an extensive subcranial-subfrontal approach, in most cases with a large coronal skin incision. At the end of the operation the skull defects were reconstructed by painstaking osteosynthesis. With this wide-open approach, the authors concluded that the application of navigation technology was valuable in only 23% of the cases and that this novel computer-based equipment should be used in a restricted manner.

From our perspective, this article overlooks the key concerns of image-guided surgery. It is trivial to conclude that navigation technology is not useful in extensive external approaches because the surgeon can rely on a large number of anatomical landmarks in these situations. It is surprising that in such wide external approaches, the authors concluded that navigation equipment was useful in more than 20% of their cases. In fact, the objective of computer-assisted surgery (CAS) is to avoid wide-open surgery (``funnel principle'') through small artificial or natural openings of the body.[1] For example, by today's state of the art, mucoceles of the paranasal sinuses are no longer treated through external approaches but through endonasal endoscopic surgery.[2] [3] For such endoscopic interventions, navigation equipment can be of considerable benefit and improves safety.

The question of the usefulness of navigational equipment resembles the discussion surrounding electrophysiological facial nerve monitoring 20 years ago. Facial nerve monitoring first seemed indicated only for complex procedures involving deep structures in the temporal bone and inner auditory canal. Now, facial nerve monitoring is less expensive, and the equipment is installed easily and quickly. Therefore, it is used routinely in ear surgery at many centers.[4] [5] Surgical navigation equipment could also follow such a life cycle.

The Bernese navigation surgery equipment marketed by Medivision SurgiGATE™, SynthesStratec, Oberdorf, Switzerland originally was developed at the Maurice E. Müller Institute for Biomechanics, University of Bern for an orthopedic application. Later, it was refined for the needs of otolaryngology (ENT) and skull base surgery.[6] Since 1997 in our ENT Department, the resulting navigation system has been used in 146 operations, mostly for endoscopic revision of recurrent polyposis[7]; for closure of CSF fistulae; for endoscopic treatment of mucoceles and choanal atresia; and for endoscopic removal of other processes in the anterior skull base, including benign and, in select cases, malignant tumors (e.g., in elderly polymorbid patients as palliative treatment). It also has been used in the lateral skull base, for example, for function-preserving removal of petrous apex cholesterol granulomas and for the surgical treatment of external ear canal atresia among others. Without navigational technology, a wide-open approach would have been needed for these interventions. As surgeons' experience with navigational devices increases, external approaches will likely become increasingly unnecessary.

It is understandable that conventional surgeons would tend to defend open surgery, which in select cases is justified (e.g., the complete removal of malignant tumors). However, there is little doubt that the use of minimally invasive surgery coupled with image-guidance and other advanced technical equipment will become increasingly widespread. This is also in the sense of fast track surgery, where economic aspects are also considered.[8]

The first author claims that he advocated and developed the upper jaw splint as a reference for navigation of the head. In fact, Carini et al.[9] reported the use of an upper jaw splint for stereotactic surgery in 1992, and Bale et al.[10] reported its use in general image-guided surgery in 1997. In direct response to these papers, the leader of the Bernese CAS project group asked Laedrach in 1997 to participate with him to realize a maxillary splint that would be compatible with the Bernese navigation system. Since 1998 the splint has been replaced by a simple cast fixed on the upper jaw by a silicone moulding mass (Coltène™, Altstätten, Switzerland).[6] [7] Finally, the photograph of Fig. 3B is not a patient with an anterior skull base pathology, but a patient treated with CAS in the ENT Department for a lesion in the petrous bone. Consequently, the leads for facial nerve monitoring are visible.

REFERENCES

• 1 Goldsmith M M, Bucholz R D, Smith K R, Nitsche N. Clinical applications of frameless stereotactic devices in neurotology: preliminary report.  Am J Otol . 1995;  16 475-479
• 2 Kennedy D W, Josephson J S, Zinreich S J, Mattox D E, Goldsmith M M. Endoscopic sinus surgery for mucoceles: a viable alternative.  Laryngoscope . 1989;  99 885-895
• 3 Lund V J. Endoscopic management of paranasal sinus mucocoeles.  J Laryngol Otol . 1998;  112 36-40
• 4 Roland P S, Meyerhoff W L. Intraoperative facial nerve monitoring: what is its appropriate role?.  Am J Otol . 1993;  14 I
• 5 Green Jr D J, Shelton C, Brackman D E. Iatrogenic facial nerve injury during otologic surgery.  Laryngoscope . 1994;  104 922-926
• 6 Caversaccio M, Bachler R, Ladrach K, Schroth G, Nolte L P, Hausler R. The ``Bernese'' frameless optical computer aided surgery system.  Comput Aided Surg . 1999;  4 328-334
• 7 Caversaccio M, Bachler R, Ladrach K, Schroth G, Nolte L P, Hausler R. Frameless computer-aided surgery system for revision endoscopic sinus surgery.  Otolaryngol Head Neck Surg . 2000;  122 808-813
• 8 Wilmore D W, Kehlet H. Management of patients in fast track surgery.  BMJ . 2001;  322 473-476
• 9 Carini S, Calcagno E, Tortori-Donati P, Andreussi L. A new model for non-invasive, reproducible fixation of a stereotaxic frame using an orthodontic resin plate. Technical note.  Acta Neurochir . 1992;  118 159-161
• 10 Bale R J, Vogele M, Freysinger W. Minimally invasive head holder to improve the performance of frameless stereotactic surgery.  Laryngoscope . 1997;  107 373-377