Endoscopic Nasoseptal Flap Repair Of Skull Base Defects: Is Addition Of A Dural Sealant Necessary?

Extended endoscopic endonasal approaches accept allowed for a minimally invasive solution for removal of a variety of ventral skull base lesions, including intradural tumors. Depending on the location of the pathological entity, various types of surgical corridors are used, such equally transcribriform, transplanum transtuberculum, transsellar, transclival, and transodontoid approaches. Often, a large skull base dural defect with a loftier-period CSF leak is created after endoscopic skull base surgery. Successful reconstruction of the cranial base defect is paramount to split up the intracranial contents from the paranasal sinus contents and to preclude postoperative CSF leakage. The vascularized pedicled nasoseptal flap (PNSF) has get the workhorse for cranial base of operations reconstruction after endoscopic skull base surgery, dramatically reducing the rate of postoperative CSF leakage since its implementation. In this report, the authors review the surgical technique and draw the operative nuances and lessons learned for successful multilayered PNSF reconstruction of cranial base of operations defects with high-flow CSF leaks created later on endoscopic skull base of operations surgery. The authors specifically highlight of import surgical pearls that are critical for successful PNSF reconstruction, including target-specific flap design and harvesting, pedicle preservation, grooming of bony defect and graft site to optimize flap adherence, multilayered closure technique, maximization of the reach of the flap, last flap positioning, and proper bolstering and buttressing of the PNSF to prevent flap dehiscence. Using this technique in 93 patients, the authors' overall postoperative CSF leak rate was 3.two%. An illustrative intraoperative video demonstrating the reconstruction technique is also presented.

Endoscopic endonasal skull base surgery has benefited from significant advances over the past decade. In the EEA to the skull base, a minimal access technique is used via the transnasal route to betrayal and remove various midline ventral skull base lesions from the frontal sinus to the craniocervical junction.¹⁵ Endoscopic endonasal approaches have many advantages over more traditional "open" transcranial approaches, including the absence of encephalon retraction and manipulation, ameliorate panoramic endoscopic visualization, and increased postoperative comfort and cosmesis for the patient. Furthermore, improved instrumentation and the introduction of 3D endoscopy accept fabricated this arroyo increasingly effective for accessing and removing ventral skull base lesions.^6,31 Nevertheless, the EEA was initially criticized for its loftier rate of postoperative CSF leakage when used to remove large intradural lesions beyond the confines of the sella, such as meningiomas, craniopharyngiomas, and clival chordomas, through large skull base dural defects. These leaks initially occurred in approximately 20%–xxx% of patients who required repair of large (> two-cm) skull base of operations defects.^9,xviii,37 Thus, the utility of the EEA was initially express to very small defects that could be successfully repaired using multilayered synthetic or autologous nonvascularized tissue grafts.

One of the most pregnant advances for the endoscopic endonasal technique was the introduction of the pedicled PNSF, also referred to every bit the Hadad-Bassagasteguy flap for closure of big skull base of operations dural defects.¹² This technique was starting time described by Oskar Hirsh in 1952 every bit a random vascularized rotational flap for the endonasal closure of CSF leaks.¹⁴ The PNSF is harvested from the mucoperichondrial and mucoperiosteal coverage of the nasal septum, and its vascular supply is the posterior septal branch of the sphenopalatine artery. Since the technique's reintroduction in the literature, multiple studies have reported increasing success with closure of large skull base defects. Currently, the incidence of postoperative CSF leaks associated with the use of the nasoseptal flap is approximately 5%, which is comparable to more standard transcranial approaches.^{3,7,13,17,18,22–24,28,xxx,34,37,38} As a result, the PNSF has get the chief workhorse for closure of large skull base defects with loftier-flow CSF leaks that develop afterward endoscopic skull base of operations surgery.³⁹ In our experience with 93 patients requiring PNSF reconstruction of large skull base of operations dural defects afterwards an EEA, nosotros accept, to appointment, been able to achieve an overall rate of postoperative CSF leakage of 3.2%. Although the technique for PNSF reconstruction has been described in the literature,^12,18 we believe that there are diverse surgical pearls and nuances that should exist emphasized to maximize successful PNSF reconstruction so that postoperative CSF leakage tin can be prevented. These aspects include target-specific flap design and harvest, pedicle preservation, grooming of bony defect and graft site, multilayer closure, maximization of the flap reach, last positioning, and proper buttressing of the flap. In the present article, nosotros review the surgical technique and describe operative nuances for vascularized PNSF reconstruction of high-flow CSF leaks later on endoscopic endonasal skull base approaches. An illustrative intraoperative video demonstrating the multilayered PNSF reconstruction technique is besides presented (Video 1).

Fiveideo 1. Intraoperative video demonstrating multilayered PNSF reconstruction of a transplanum transtuberculum skull base dural defect subsequently endoscopic endonasal removal of a retrochiasmatic craniopharyngioma. Modified with permission from Liu JK, Eloy JA: Endoscopic endonasal transplanum transtuberculum approach for resection of retrochiasmatic craniopharyngioma. J Neurosurg 32 (Suppl):E2, 2022. Click here to view with Media Histrion. Click here to view with Quicktime.

Surgical Technique

Patient Positioning and Preparation

At our institution, we use a two-surgeon technique to allow for 3–iv hands or instruments to be introduced into the nose, as popularized by Kassam et al.^15,xvi This is performed with a neurosurgeon and an otolaryngologist who use a bi-nostril technique without a nasal speculum. We believe that the 2-surgeon technique has several advantages. I advantage is the dynamic in-and-out movement of the endoscope to increase depth perception. The other is that the 2-handed microsurgical dissection can be maintained by the neurosurgeon while the endoscope is directed by the otolaryngologist. When performing the PNSF reconstruction of the skull base defect, the ii-surgeon, 3- to 4-mitt technique has a significant reward over a unmarried-surgeon technique in that the endoscope tin be held in i manus while a dissection musical instrument or suction can be held in the other manus.

Later induction of general anesthesia, the patient is positioned supine with the head in 3-pin fixation in a Mayfield head holder. We adopt to secure the endotracheal tube to the patient's left side to allow access past both surgeons from the patient's right side. The patient's head is slightly bent laterally to the left shoulder and slightly rotated to the correct side to facilitate comfortable access to both nostrils by the surgical team. For standard transsphenoidal transsellar approaches, the face remains parallel to the floor in a neutral position. For transcribriform and transplanum transtuberculum approaches, the head is also slightly extended to facilitate access to the anterior skull base. For transclival or transodontoid approaches, the head is slightly flexed to facilitate admission to the infrasellar clival and odontoid regions. Image guidance with either CT or MRI is conducted in all of our cases.

In full general, we adopt not to use postoperative lumbar drainage because of the risks associated with intracranial hypotension and tension pneumocephalus. In our experience, lumbar drainage has non decreased the rate of postoperative CSF leakage. Furthermore, patients without an indwelling lumbar drain are able to mobilize earlier with less run a risk of thromboembolic and pulmonary complications.^10,23 The nose and nostrils are prepared with povidone-iodine (Betadine) solution followed by placement of oxymetazoline hydrochloride (Afrin)–soaked pledgets. The abdomen and right thigh are also prepared for potential autologous fatty and/or fascia lata graft harvesting for multilayer reconstruction prior to last placement of the PNSF.

Flap Blueprint and Harvest of the Nasoseptal Flap

The details of how we perform the initial endoscopic endonasal approach to the ventral cranial base have been previously described.^22,23 In general, we prefer to harvest the PNSF at the beginning of the functioning and rotate it into the posterior nasopharynx or maxillary sinus during the cranial base exposure and tumor removal until afterward employ for reconstruction. Care is taken to ensure that the vascular pedicle is protected from trauma to forestall compromise of the flap. We apply a similar method to Hadad and colleagues¹² to harvest the PNSF. Nosotros prefer to use a No. 15 bract knife rather than a fine-tipped monopolar cautery when making the incisions along the nasoseptal mucosa. Nosotros believe that using a knife bract to make the advisable cuts ultimately increases the available surface area of the PNSF for optimal coverage by fugitive tissue retraction and shrinkage associated with electrocautery. Furthermore, the increased vascularity at the edges of the flap may play a role in adherence to the skull base defect. Abstention of electrocautery may likewise ameliorate donor-site re-mucosalization of the nasal septum by decreasing thermal trauma at the edge of the remaining nasoseptal tissue.

The get-go incision is fabricated at the junction betwixt the floor of the nose and the nasal septum starting from a posterior to inductive management. In cases in which a larger PNSF is desired (as in cases of transcribriform defects from orbit to orbit), this incision is taken more laterally along the floor of the nose to increase the width of the flap. The 2nd incision is fabricated from the most inferior aspect of the sphenoid opening and avant-garde superiorly and anteriorly until the desired length is reached. This incision can be taken as far anteriorly equally the septocolumellar junction if a longer flap is needed (as in transcribriform defects extending to the posterior table of the frontal sinus). During this 2d incision, it is important to preserve the olfactory mucosa located posterosuperiorly to foreclose postoperative anosmia. The tertiary incision involves making a vertical cut connecting the most anterior aspect of the previous two incisions. It is important not to perform this incision before the other 2 incisions as to prevent pooling of blood posteriorly that can obstruct visualization of the field. At this juncture, the nasoseptal flap is elevated with a Cottle lift in a submucoperichondrial and submucoperiosteal airplane from an inductive to posterior direction until the choana is reached. Lastly, a relaxing incision is made along the arc of the choana to increase the surgical liberty (that is, the range of rotation) of the flap. By taking this incision as far lateral along the choanal arch, 1 can significantly increase the flap'south mobilization and attain.

It is important to blueprint the PNSF tailored to the location and the anticipated size of the skull base defect that volition be created to access the particular tumor. We term this "target-specific flap design." For transcribriform approaches for olfactory groove meningiomas or sinonasal tumors requiring large cribriform resections, we prefer to harvest big flaps that extend as far anteriorly every bit the septocolumellar junction. These transcribriform defects are also wider, extending from one medial orbital wall to the other. Therefore, the width of the flap is enlarged by making the inferior incision more laterally along the mucoperiosteum of the nasal flooring (hard palate). To ensure adequate coverage of the skull base defect, it is better to overestimate the defect size and harvest a larger flap than to have a smaller flap with suboptimal coverage.

Preparing the Defect

Later tumor removal and subsequent meticulous hemostasis is achieved, reconstruction of the cranial base defect begins with preparing the bony defect site (recipient) for the PNSF (donor). It is of import to strip the bony ventral skull base of operations and sphenoid sinus of any secretory mucosa to allow flap adherence to the os. We typically despoil approximately 1 cm of mucosa around the bony defect, so as to avert whatsoever trapped mucosa betwixt the layers of reconstruction, which tin event in postoperative intracranial mucocele formation.^iv Placing the flap over secretory mucosa likewise risks flap dehiscence from the skull base of operations. For successful flap adherence of the PNSF to the skull base, at that place must exist acceptable contact between the mucoperichondrial/mucoperiosteal surface of the flap and the denuded bone. Additionally, in transplanum and transsellar approaches the unabridged sphenoid sinus is denuded to prevent sphenoid sinus mucocele formation. This also includes denuding the mucosa of the lateral recesses of the sphenoid sinus.

Multilayer Reconstruction of Skull Base of operations Defect

Meticulous multilayer reconstruction of the skull base dural defect is critical for preventing postoperative CSF leakage (Video 1).^2,22,23,37 The skull base of operations dural defect is initially converted from a high-flow CSF leak country to a depression-menses CSF leak state by placing a piece of autologous fascia lata to embrace the defect (Fig. 1A and B). Information technology is important to harvest a piece of fascia lata that is larger than the dimensions of the dural defect. We use precut pieces of Gelfoam of different sizes as templates to estimate the dimensions of the dural defect.

For transcribriform and transclival defects, we adopt to use an inlay technique and then that the edges of the fascia are tucked underneath the dural edges. For larger transcribriform defects, nosotros place an additional layer of acellular dermal allograft as a combined inlay/overlay layer.^10,22,26 Nonetheless, we prefer to use an overlay technique for transplanum transtuberculum defects because the optic canals and optic sheaths are ofttimes exposed in this procedure, especially for handling of tuberculum sellae meningiomas.^23,25 Placing the graft on the exterior as opposed to the inside will decrease the hazard of graft compression of the exposed optic nerves (Fig. 1A and B). For transsellar defects, we besides prefer to apply an overlay technique considering nosotros ordinarily perform wide dural openings that prohibit any graft to be tucked underneath as an inlay. For larger sellar defects, equally in pituitary macroadenomas, we occasionally insert a piece of autologous fat in the sellar defect before placement of the fascia lata onlay graft. A monolayer of Surgicel is then placed over the fascia graft to hold it in position to preclude graft migration prior to placement of the PNSF (Fig. 1C and D). At this juncture, in that location should be almost no testify of CSF egress from the dural repair before proceeding to the next stride of nasoseptal flap placement. If needed, a second piece of fascia lata followed by another layer of Surgicel tin can exist placed to stop any further CSF egress.

Rotation and Positioning of the PNSF

The vascularized PNSF is and so brought upwards from the nasopharynx or maxillary sinus and rotated toward the ventral skull base of operations repair (Fig. 2A). It is essential to maintain proper orientation of the flap so that the mucoperichondrial/mucoperiosteal surface of the PNSF is in direct contact with the ventral skull base defect. It is also important to ensure that the vascular pedicle is not twisted upon itself but maintains a uniform directionality. To ensure that the "reach" of the PNSF is maximally optimized, we aggressively remove the rostrum and flooring of the sphenoid bone during the skull base of operations exposure so that the flap is not hinged on this ledge, which tends to shorten the accomplish of the flap. The reach of the flap can also be lengthened past extending the incision at the proximal base of the flap near the vascular pedicle along the superior arc of the choana as mentioned higher up.

Using the ii-surgeon technique, the PNSF is advisedly positioned over the skull base repair. Cottonoid paddies are used to apply gentle pressure on the flap from a proximal to distal mode to rid whatever trapped air bubbles beneath the PNSF (Fig. 2B and C). This step ensures a skillful seal against the skull base so as to avoid the risk of flap dehiscence. Another unmarried layer of Surgicel is placed effectually the edges of the PNSF to concord it in position and prevent flap migration (Fig. 2D). In our initial experience, we applied a dural sealant (fibrin glue or DuraSeal) over the PNSF repair at this juncture. Even so, in a contempo retrospective review, nosotros found that the improver of a dural sealant did not significantly subtract the rate of postoperative CSF leakage.² Therefore, we have stopped using dural sealants when performing PNSF reconstruction in the aforementioned fashion, which has also decreased the surgical costs. We likewise believe that adding a layer of dural sealant prevents maximal buttressing force of the Gelfoam and Merocel packing confronting the PNSF repair. Additionally, nosotros believe that the dural sealant has the potential to drip underneath the free edges of the PNSF and lift the flap away from the bone during the sealant expansion, thus risking flap dehiscence.

Bolstering and Buttressing the PNSF

Proper buttressing of the PNSF is also critical to preventing postoperative flap dehiscence. The PNSF repair is and then bolstered with several pieces of 2.5 × two.5–cm Gentamicin-soaked Gelfoam pledgets (Fig. 3A and B). An initial layer is placed directly on the PNSF repair so compressed with cottonoid paddies with gentle suction. This stride is followed past the placement of a second layer of Gelfoam. An inflatable Merocel nasal tampon lathered with Bacitracin ointment is then placed into the nasal cavity to buttress the repair. The packing expands the dead infinite in the nasal cavity after it becomes hydrated with Gentamicin irrigation (Fig. 3C and D). This provides buttressing support up confronting the PNSF repair to optimize flap adherence to the os.

Although some have used a Foley catheter balloon to buttress the PNSF repair, we prefer to use the inflatable Merocel nasal tampon. In our opinion, the Merocel tampon expands in such a manner to provide a tighter packing of the nasal cavity dead space while applying uniform pressure to the skull base repair. Because the Foley balloon is spherical in shape, the balloon has less direct contact on the PNSF repair than does the Merocel pack that expands to fill the dead space. The Merocel pack, in general, is less invasive and more comfortable for the patient while avoiding the risk of premature inadvertent removal by the patient or nursing staff.

Postoperative Management

The patient is maintained on postoperative antibiotics with a third-generation cephalosporin or a penicillin-based antibody with β-lactamase for about 10–12 days after surgery until the Merocel packing is removed by nasal endoscopy. The patient receives stool softeners and is instructed to avoid Valsalva maneuvers, nose blowing, or activities that can raise intracranial pressure level. Additionally, we do not routinely use postoperative lumbar drainage to avoid complications associated with intracranial hypotension and tension pneumocephalus considering the patient is already in a CSF hypovolemic country at the terminate of the surgery.^five We have observed that by non placing an indwelling lumbar drain, patients are able to ambulate earlier and minimize their potential risks for thromboembolic events. Furthermore, patients are discharged from the infirmary earlier, thereby promoting shorter infirmary stays. In our experience of using the aforementioned reconstruction technique in 93 patients, we have observed a postoperative CSF leak rate of 3.2%. These leaks were all successfully repaired past repositioning and rebolstering the same PNSF on top of a multilayer reconstruction.

Management of Postoperative CSF Leaks

Of 93 patients who underwent multilayered PNSF reconstruction of high-menstruum CSF leaks subsequently endoscopic skull base surgery, 3 suffered a postoperative CSF leak. All iii patients underwent endoscopic endonasal reexploration and revision of the skull base repair using the same viable PNSF. In that location were no further leaks subsequently the revision repair. Interestingly, all iii patients had undergone a transplanum transtuberculum approach to a suprasellar tumor. The skull base defect created past this arroyo is generally big (approximately 5 cm²) and communicates freely with an opened suprasellar arachnoid cistern and, in some cases, a fenestrated floor of the third ventricle. Thus, some have suggested that transplanum defects have a higher chance of postoperative CSF leakage than other locations such as transcribriform or transsellar.^9,37

Each failure was critically analyzed for the potential cause of the leak. In i patient delayed CSF rhinorrhea developed 4 weeks after surgery, about 1 week afterward a routine outpatient follow-up debridement performed via nasal endoscopy. Nosotros postulate that disturbance of the repair may have occurred during the debridement. The patient underwent endoscopic reexploration, and the nasoseptal flap was noted to be partially displaced. The defect was successfully repaired with an acellular dermal allograft followed by repositioning the same PNSF. The 2d patient was noted to have high CSF egress during the dural opening part of the surgery. Benign intracranial hypertension was suspected, and a postoperative lumbar bleed was therefore placed postoperatively for v days. Ii days later on removing the lumbar bleed, the patient presented with a CSF leak. A lumboperitoneal shunt was inserted, and a revision of the PNSF repair was undertaken using the same flap. The third patient adult delayed intraventricular tension pneumocephalus ane week afterward surgery. An emergency ventricular catheter was placed to aspirate air, and endoscopic reexploration was performed thereafter. A ball-valve leak was noted in the repair, and successful revision of the repair was performed using the same fascia lata graft and PNSF.

Discussion

Endoscopic endonasal approaches to admission ventral skull base pathologies have become increasingly constructive over the last decade (Fig. four). In properly selected cases, this approach provides various advantages over more than conventional open transcranial methods to admission and remove lesions of the midline ventral skull base, sellar region, and parasellar region, including avoidance of a transfacial or transcranial incision, craniotomy or transfacial osteotomies, and risks associated with brain retraction and manipulation.^{11,15,xvi,18–20,22,23,25,26,33} Furthermore, this approach offers panoramic visualization of ventral skull base structures from the frontal sinuses to the craniocervical junction with the assist of angled endoscopes.^one,22,23

Initially, the EEAs were restricted to the removal of small lesions through smaller skull base defects (< 1 cm). These smaller defects were usually airtight using a combination of nonvascularized costless tissue and synthetic grafts, applied in a variety of methods. The success rate for closing modest lesions with this method was approximately 95%, which showed EEAs to exist an effective method when the performance required creating a minor skull base of operations defect.¹² Still, i of the major criticisms of EEAs during their infancy was the relatively high rate of postoperative CSF leaks when the approach was used for removal of larger lesions through a large (> two-cm) defect when using the same multilayered nonvascularized free graft reconstruction technique. This type of closure began with a subdural inlay graft of collagen matrix to eliminate intradural expressionless space and was followed by an extradural inlay graft of acellular dermis to provide closure of the cranial defect. If an epidural graft was bereft or a more than complete closure was desired, the application of grafts over the defect on the nasal side was oftentimes performed, with careful denudation of the surrounding mucosa to prevent mucocele germination. Finally, the grafts would exist bolstered by a combination of absorbable packing, gelatin sponge squares, and possibly synthetic glue.³⁹ The basic premise established by the closure of traumatic, idiopathic, and smaller skull base of operations defects was expanded upon by using unlike materials for closure, namely endogenous nonvascularized tissue grafts, including autologous fat grafts, fascia lata grafts, temporalis fascia grafts, and occasionally autologous bone grafts. These grafts would be used at various points in the closure, either as subdural inlay grafts or as overlay grafts for the defect.^{eight,21,32,36} However, even with optimal closure, endoscopic reconstruction of larger dural defects resulted in an unacceptably high CSF leak rate of approximately 20%–thirty%.³⁹ Furthermore, the utilise of vascularized flaps for the repair of dural defects in transcranial approaches, including pericranial, galeal, and temporoparietal flaps, were not feasible for minimally invasive endonasal approaches. Non only did externally accessing these cranial flaps contradict the minimal access nature of EEAs, merely information technology could drastically increase the risk for postoperative morbidity and infection.^seven,12

The high postoperative CSF leak rate associated with EEAs for large skull base lesions limited this approach to only small lesions, leaving larger lesions for traditional transcranial approaches. All the same, the recent appearance of pedicled endonasal mucosal flaps for repair of large skull base of operations defects considerably expanded the role of EEAs in accessing and removing these larger lesions. Initially, the intranasal flaps were taken from random locations, with varied success.^35,39 Of these, the PNSF has been the most widely studied and has gained the most popularity for closure of big skull base defects created after EEAs. This flap consists of a neurovascular pedicled flap from the mucoperiosteum and mucoperichondrium of the nasal septum, which is supplied by the posterior septal branch of the sphenopalatine artery.¹² The greatest advantage of this flap is that it tin be harvested endoscopically before creating the skull base defect, thereby eliminating the need for external flap harvesting. Furthermore, this flap provides the same advantages as other vascularized flaps, namely faster healing and a lower incidence of graft migration. Some other major advantage to this flap is that it provides a very big expanse (approximately 25 cmⁱⁱ) for the coverage of large defects created from EEAs.⁷ The PNSF is effective in covering defects greater than 6 cm in the anterior cranial fossa, particularly the transcribriform defects that extend from the posterior table of the frontal sinuses to the planum sphenoidale in the sagittal plane and between both orbits in the coronal plane.^22,26,38 All the same, maximally extensive defects from multiple-corridor EEAs, such as those that extend from the sella turcica to the posterior table of the frontal sinus, may crave bilateral PNSFs or other forms of repair.^22,27,29

Conclusions

The PNSF used in conjunction with a multilayered reconstruction is an constructive method for repair of high-menstruum CSF leaks from large skull base defects created after endoscopic skull base surgery. The fundamental aspects to successful reconstruction include meticulous multilayered reconstruction performed by 2 surgeons (the 3- to four-paw technique), conscientious grooming of the skull base defect and graft site, accurate flap design and preservation of the vascular pedicle with avoidance of trauma to the flap, and optimal positioning and buttressing of the PNSF repair. Careful consideration of all these steps in the PNSF reconstruction is critical to minimizing postoperative CSF leakage.

Disclosure

The authors report no conflict of interest apropos the materials or methods used in this report or the findings specified in this paper.

Author contributions to the study and manuscript preparation include the following. Conception and blueprint: Liu, Eloy. Acquisition of data: all authors. Analysis and interpretation of data: all authors. Drafting the article: Liu, Schmidt, Choudhry. Critically revising the article: Liu, Schmidt, Eloy. Reviewed submitted version of manuscript: Liu, Schmidt. Approved the last version of the manuscript on behalf of all authors: Liu. Study supervision: Liu, Eloy.

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