This series reviews our initial experience with the NSF at an academic center where both the otolaryngologists and neurosurgeons are trained endoscopic surgeons. All cases are done by otolaryngologist and neurosurgeons working together. The NSF is harvested at the onset of the case to preserve its blood supply prior to the septectomy. In general, for a right-handed surgeon, the NSF is raised on the right side. The middle turbinate on the right is resected along with the ethmoids and the posterior septum is then taken down to create a corridor that allows instruments to be passed on the left side and to create room for two surgeons to work in tandem. A left-sided NSF is used when the right side of the NSF or its blood supply is threatened by tumor extension or preoperative embolization.
We examined factors associated with the NSF selection for use, successful harvest, application, and outcome. A total of 28 patients had 32 NSFs harvested. Two additional patients had a total of 3 middle turbinate flaps. Of this group, 25 patients had an intracranial defect, and 20 had a dural defect. Of the two patients who had a middle turbinate flap, one patient was unsuitable for an NSF due to an absent septum. The other patient had focal defects in the fovea ethmoidalis bilaterally that would have required significant tissue resection to prepare the skull base for an NSF. Therefore, due to its proximity and the limited size of the defect, the middle turbinate flap was a simple alternative with minimum morbidity. Thirty NSFs (94%) were successfully harvested, while 2 (6%) NSFs were lost intraoperatively. One NSF was split during harvest due to a large longitudinal septal spur. The septal spur was associated with thinning and friability of the flap mucosa. Several patients in the series had a history of prior nasal septal surgery, but these data were not retrievable in the chart review. While the author was able to elevate NSFs in this situation, the procedure is more difficult.
Overall, none of the 20 patients had a postoperative CSF leak in our series, supporting the initial literature indicating a CSF leak rate of 5%. Prior nasopharyngeal radiation is found to be a risk factor for NSF necrosis (p
0.013). Only 2 of 32 flaps (6%) necrosed postoperatively, and yet no CSF leak occurred in either case. One of the two cases developed a partial necrosis, while the second case had a complete necrosis. Of note, both of these patients went on to postoperative irradiation, one with intensity-modulated radiation therapy and the other with proton beam therapy to an area outside the prior radiation field. A previous report of 43 patients having closure with the NSF found a CSF leak rate of 5%.18
It is likely that as our experience increases with the NSF, and larger defects are approached, our CSF leak rate will increase; however, these data support the use of NSF closure for smaller dural defects, up to 4 to 5 cm2
. Our experience with these smaller defects is that the CSF leak rate is comparable to that of open procedures. A few large dural defects, up to 6.2 cm2
, were also successfully closed, indicating that the NSF is also useful for large defects of the anterior and central skull base.
A 0% leak rate prevents further analysis of factors associated with CSF leak. In the early postoperative period, many patients likely have a CSF leak since the wound is not closed in a watertight fashion and the wound requires time to mucosalize. Further, most patients are noted to have nasal drainage while the merocel packs are in (even those without CSF leak noted during surgery). However, no patients had detectable rhinorrhea or CSF at the time of merocel packing removal on postoperative day 10. Most patients in this series did not frequently complain of associated symptoms of CSF leak, such as headache or meningismus, in the first week after surgery. The follow-up time of 8.3 months should be sufficient to identify CSF leaks due to failure of wound closure. As initially described by Hadad and colleagues,18
a fat graft can be used in conjunction with an NSF or it can be lined directly on the dural reconstruction. Our technique differs in that we routinely place extracranial fat between the Duragen and the flap. This may explain why the two cases with NSF failure healed the defect.
One criticism of the NSF is that it may not cover the wound completely and that it may shrink by 20 to 40% over time. In our experience, when fat was not used, the NSF was applied directly on the defect and covered it entirely. When fat was used, the fat covered the entire defect, but the NSF did not always cover the entire fat graft. The fact that we had no cases of CSF leak in either situation implies that the wounds have healed. Intuitively it would seem that NSF provides a base of healthy mucosa that is expected to remucosalize over the nonvascularized graft (fat or Duragen) through epithelial cellular migration. Once a healthy base of mucosalized epithelium is established, it is unlikely that flap shrinkage would subsequently result in a CSF leak. Further, given this paradigm, it seems likely that if a small CSF leak persisted after the first closure attempt, a subsequent repair with fat graft or free mucosa could be attempted. Flap shrinkage has been noted postoperatively when the pedicle is free-floating in the air, and it is recommended that the pedicle of the flap be lined on bone along its length to reduce shrinkage. There have been no cases of late CSF leak in our series to suggest the NSF can shrink enough to pull off the wound. In our series, the flap was not routinely sutured in place, and watertight closures were not achieved at the time of surgery. The 100% success rate indicates this is an acceptable approach.
Fourteen patients required radiation after surgery. For malignant lesions of paranasal sinuses, patients are recommended to start radiation within 6 weeks of surgery. In the event of the two patients with NSF failure but no CSF leak identified, we still recommended proceeding with radiation in a timely manner. The average time to radiation in this series was 7.5 (SD, 3.4) weeks. Five patients were delayed longer than 6 weeks. Delays were attributable to patient delays (1), need for proton therapy out of the area for chordoma (2), and need for radiation to a pituitary adenoma (2) (where the 6-week rule is not followed). Wound healing issues were not related to the delay to proceed with radiation.
The NSF can be used to close extracranial wounds without a CSF leak as well. If the NSF is being considered for use, it must be raised at the beginning of the case to preserve it. We therefore considered if lining wounds without CSF leaks would provide benefit to the patient. Five patients had an intracranial defect without CSF leak, and five patients had a flap elevated without breach of the skull base bone. Four of these patients with extracranial defect had extensive resection from the pterygoid and ITF. The other patient had a sphenoclival lesion respected. Two of the patients with ITF lesions had had prior radiation and the flap was used to prevent radionecrosis. One of the patients with an ITF lesion had nasopharyngeal extension and had an exposed carotid artery after transcervical exposure of the carotid and dissection of tumor off the carotid artery. The carotid artery was lined with the NSF to prevent carotid infection and leakage of saliva into the neck wound. The other wounds were lined with the NSF to decrease healing time by encouraging earlier mucosalization and decreased crusting. Furthermore, the NSF is still available if a revision surgery is needed.
While inlay bone is used for some cases of CSF leak repair not associated with tumor resection, rigid materials and fixation are avoided after tumor resections. The technique described for endoscopic closure of skull base defects relies on a soft tissue closure without rigid fixation.12
After open anterior craniofacial resection, some surgeons will use rigid material to support the anterior cranial fossa in conjunction with a pericranial flap to prevent brain herniation in large defects.20
However the exact definition of a “large lesion” is not clear in the literature. In our experience at UCSF over the past 20 years, we have routinely repaired defects involving the bilateral ethmoids and sphenoid planum without rigid fixation and have not witnessed brain herniation.21
Furthermore, there is concern that rigid material may eventually extrude, leading to a late CSF leak, or act as a sequestrum promoting an infectious complication. Therefore, the current approach described for endoscopic closure does not deviate significantly from standard techniques used in open craniotomy. Kassam and associates describe using an inlay graft of Duragen deep to the dura, and a second layer of acellular dermis (Alloderm; LifeCell Corporation, Branchburg, NJ) external to the dura.12
This is followed by a fat graft and the NSF. Kassam et al currently avoid the use of an intervening layer of fat and lay the NSF directly on the wound (verbal communication). Our technique differs in that we do not apply a second layer of acellular dermis external to the dura. Further, in this series, we have used DuraSeal, a polyethylene glycol hydrogel sealant, intervening between the fat graft and NSF. The wound is left relatively undisturbed for up to 8 weeks and may account for the tissue ingrowth and vascularization of the fat graft. However, in principle, when the fat graft can be maintained in position prior to placement of the NSF, it seems intuitively reasonable to avoid intervening tissue sealants to accelerate vascularization of the free tissue fat graft and we currently try to avoid intervening material between the NSF and the next layer of tissue. We do not routinely suture in any layer of the reconstruction except when the flap is placed in a manner that is susceptible to retraction (orbit, ITF).
This series of NSF reports on our experience starting with our first NSF at an academic center. The NSF was found to be easily harvested. Snyderman et al examined surgical skill acquisition and recommend a staged approach for learning endoscopic dissection techniques.22
We lost one NSF to a novice surgeon due to tissue handling and surgeon skill should be considered. Overall though, the NSF appears easy to harvest and manipulate. Factors that may predict difficulty raising the NSF include deviated septum, septal spurs, an existing perforation, and prior septal surgery. Other factors that should be considered in the patient history include cocaine use, vasculitic disease, or a predisposition to poor wound healing such as chronic steroid therapy or hypothyroidism.
This series also illustrates when the NSF flap does not appear appropriate or is unavailable. In one case, the NSF was not available due to septal perforation that resulted from the prior trans-sphenoidal surgery. In a second patient, harvest of the flap and preparation of the skull base for the flap to cover the roof of both ethmoids would have required extensive dissection. Use of the middle turbinate bilaterally sufficed in this case.
Potential morbidity exists with use of the NSF. If the flap is taken too high along the skull base, olfactory fibers can be injured which can result in anosmia. In cases where the olfactory bulb is intact, if the flap is elevated on one side, then patients should have functioning olfactory fibers on the contralateral side, but potential for complete anosmia exists. These data were not captured in our retrospective review at this time, but several patients have complained of decreased olfaction after surgery. Loss of olfaction can also occur due to injury from the tumor or resection of the tumor. Nasal crusting is pronounced for several weeks after surgery and may persist indefinitely. However, all patients in our experience are manageable with home saline irrigations and infrequent debridement after the initial postoperative period. Antibiotics are not routinely used except for cases of frank purulent discharge.