Lengthening the Nasoseptal Flap Pedicle with Extended Dissection into the Pterygopalatine Fossa: A Cadaveric Anatomic Study

Background: The nasoseptal flap (NSF), pedicled on the posterior septal branch of the sphenopalatine artery (SPA), is a versatile method for reconstructing cranial base defects. Since its introduction in 2006, use of the NSF has significantly reduced the incidence of cerebrospinal fluid leak from 20 to 30% to less than 5% during endoscopic skull base procedures. The NSF may be limited, however, in its reach to the anterior-most aspects of anterior cranial base defects, or for full coverage of defects from transclival approaches to the posterior fossa. In these cases where NSF length may not be sufficient, further reconstruction methods may be necessary. Releasing the NSF pedicle from the SPA foramen and extending dissection into the pterygopalatine fossa (PPF) may considerably improve flap reach and usable surface area.

Objective: To quantify increases in pedicle length and NSF reach through extended pedicle dissection into the PPF through cadaveric dissections.

Methods: Twelve cadaveric dissections were performed in six specimens fixed with methanol. The length of the septal mucosa from the choana to the columella was obtained first. Following standard NSF harvest to the level of the SPA foramen, the distance from the anterior edge of the flap to the anterior nasal spine while pulling the flap anteriorly was measured. As dissection into the SPA foramen and PPF continued, interval measurements from the nasal spine to the anterior edge of the flap were completed. All the measurements were obtained with anterior traction of the flap, moving it out of the nasal cavity through the nostril. Three further measurements were obtained: maximum reach following release from the SPA foramen, dissection to and release of the internal maxillary artery (IMAX), and following transection of the descending palatine artery (DPA).

Results: Twelve sides of six cadavers were included in the study. The mean length of the nasoseptal flap after standard harvest was 1.91 ± 0.40 cm from the nasal spine with a maximum reach of 9.39 ± 0.39 cm. The mean length after bony release surrounding the SPA foramen was 2.52 ± 0.61 cm from the nasal spine with a maximum reach of 9.75 ± 1.06 cm. The mean length after full dissection of the SPA/IMAX was 4.93 ± 0.89 cm from the nasal spine with a maximum reach of 12.16 ± 0.54 cm. The mean length after transection of the DPA was 6.18 ± 0.68 cm from the nasal spine with a maximum reach of 13.41 ± 0.75 cm.

Conclusion: In this cadaveric study, extended pedicle dissection of the NSF to the SPA/IMAX markedly improves the potential length and reach of the flap. This technique may provide a feasible option for reconstruction of large anterior skull base and craniocervical junction defects. Further studies are warranted to validate findings in a clinical setting and determine long-term viability.