Morphometric and Clinical Analysis of the “1.5 Approach” - A Novel Approach to the Sphenoid Sinus with Preservation of Nasoseptal Flap

Objective: The use of a pedicled nasoseptal flap (NSF) for repair of high-flow leaks is well established, and is typically raised at the beginning of the procedure. For endoscopic endonasal procedures that do not create high-flow cerebrospinal fluid (CSF) leak, reconstruction with a pedicled NSF is rarely needed. Preservation of the vascular pedicle of the NSF is important in case a significant leak is encountered, or for future use. We describe one of our NSF preservation techniques entitled the “1.5 Approach,” and include morphometric analysis of the exposure obtained. This is compared with standard unilateral and bilateral, complete sphenoidotomies. Clinical data from operative cases that utilized the 1.5 Approach are also presented.

Design: The 1.5 Approach is a unilateral, complete sphenoidotomy (“1”) on one side, with a limited sphenoidotomy above the sphenoid ostium (“0.5”) on the contralateral side, which preserves the vascular pedicle to the NSF. Ten formalin-fixed cadaver heads were utilized for morphometric analysis. Using frameless neuro-navigation and endoscopic visualization, the sagittal and axial range of instrument access to the sphenoid sinus was measured based on the nasal sill. Comparison of sphenoid sinus access was made for standard unilateral sphenoidotomy, our 1.5 Approach, and bilateral complete sphenoidotomies. The size of the sphenoidotomies was measured in the sagittal and axial plane for the three approaches. Angles for instrumentation within the sphenoid sinus were evaluated. Finally, a retrospective review was performed on patients in whom the 1.5 Approach was performed. Preservation of the NSF, pathology, post-operative CSF leakage, site and extent of resection were analyzed.

Results: Compared with the unilateral approach, the 1.5 approach adds 4.7mm (p = 0.001) and 3.9° (p = 0.001) range of instrument access in the axial plane. Performing the contralateral, limited sphenoidotomy with the 1.5 Approach adds 10.3mm (p = 0.001) to the sphenoidotomy in the axial plane. When the limited (“0.5”) sphenoidotomy is converted into a complete sphenoidotomy, there is an increase of 9.0mm (p = 0.001) and 7.2° (p = 0.001) in the range of instrument access in the sagittal plane, and the size of the sphenoidotomy is increased by 9mm (p = 0.001). The increase in range of instrumentation and size of sphenoidotomy is only in the sagittal plane below the base of the sella. The face of the sella is completely visualized and reached in both 1.5 and bilateral complete sphenoidotomies. Thirty-five patients underwent endoscopic transphenoidal pituitary surgery using the 1.5 Approach. Preservation of the NSF was achieved in all 35 cases. Gross total resection was achieved in 94%. Tumor resection was limited by cavernous sinus invasion, not exposure. A low-flow intraoperative CSF leak occurred in 8.6% (3/35) of cases and was repaired with a dural substitute. There were no post-operative CSF leaks.

Conclusions: The 1.5 Approach provides excellent access to sphenoid and sellar pathology, with preservation of the NSF. It significantly improves access over a unilateral approach by adding binaral surgery to the sphenoid sinus. Our morphometric analysis and clinical experience reveal that the limited sphenoidotomy of the 1.5 Approach provides comparable access to the sphenoid sinus and sellar pathology.