Medial and Superior Orbital Decompression: Improving Access in Endonasal Endoscopic Lateral Frontal Sinus Surgery

Object: Lateral frontal sinus surgery is technically challenging due to limiting bony conditions and the orbit. Previous studies define the most lateral point accessible with an instrument in the frontal sinus, under visual control, based on well-known endoscopic surgical procedures. We present a method, based on the Draf III approach, which allows increased access to the lateral frontal sinus by removing a limited portion of the supero-medial wall of the orbit with preservation of the periorbita. The anatomical details of the frontal recess and lamina papyracea which enable this procedure are described.

Methods: Twenty embalmed heads were studied using thin cut CT scans for the purpose of neuronavigation. The heads were then registered with our neuronavigation system (Stryker®). A Draf II, III and Draf III with medial and superior orbital decompression (MSOD) and preservation of the periorbita were performed. Measurements were taken from the midline, defined by the crista gali, to the most lateral point of the frontal sinus reached under visual control during each surgical procedure. Average distance, difference between the distances achieved during each approach, as well as calculated average and median were obtained.

Results: Of the 20 heads, twelve were excluded due to under-pneumatization of the frontal sinuses allowing lateral access with a limited Draf II or III approach. A total of 8 cadaver heads, 16 sides, were studied. Excellent accuracy was achieved in all cases using the neuronavigation, with a range of error in registration from 0.6 to 0.8mm. The average distance between the midline and most lateral point on the left achieved with the Draf II, Draf III, and Draf III with MSOD was 19.08mm, 23.74mm, and 30.39mm, respectively. On the right side the average distance between the midline Draf II, Draf III, and Draf III with MSOD was 18.66mm, 25.1mm, and 32.19mm, respectively. The difference between the pure Draf III and Draf III + PMOD procedure was also calculated; the average difference on the left was 6.65mm and 7.09mm on the right.

Conclusion: A rate limiting factor in endoscopic surgery of the frontal sinus is limited visualization and instrumentation of the lateral frontal sinus. Although the classic Draf II and III approaches can access the lateral limit of the frontal sinus in several cadavers, well pneumatized frontal sinuses restrict access to laterally extending lesions. The Draf III with MSOD allows extended surgical access to the lateral regions of the frontal sinus. The technique allows better visualization and instrumentation with minimal removal of the orbital segment of the frontal bone anterior and superior to the anterior ethmoid artery and preservation of the periorbita. Careful analysis of pre-operative imaging may allow consideration of this extended approach for frontal sinus and anterior cranial fossa pathologies.