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Endoscopic Reconstruction of Surgically Created Skull Base Defects: A Systematic Review Ethan Soudry, Justin H. Turner, Jayakar V. Nayak and Peter H. Hwang Otolaryngology -- Head and Neck Surgery 2014 150: 730 originally published online 3 February 2014 DOI: 10.1177/0194599814520685 The online version of this article can be found at: http://oto.sagepub.com/content/150/5/730

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Systematic Review

Endoscopic Reconstruction of Surgically Created Skull Base Defects: A Systematic Review

Otolaryngology– Head and Neck Surgery 2014, Vol. 150(5) 730–738 Ó American Academy of Otolaryngology—Head and Neck Surgery Foundation 2014 Reprints and permission: sagepub.com/journalsPermissions.nav DOI: 10.1177/0194599814520685 http://otojournal.org

Ethan Soudry, MD1, Justin H. Turner, MD, PhD2, Jayakar V. Nayak, MD, PhD1, and Peter H. Hwang, MD1

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

Received August 22, 2013; revised November 11, 2013; accepted January 2, 2014.

Abstract Objectives. To systematically review the literature concerning techniques of closure of endoscopically created skull base defects based on site of skull base defect and flow rate of cerebrospinal fluid (CSF).

D

Data Sources. PubMed, SCOPUS, and Cochrane databases. Review Methods. A comprehensive systematic literature review. Results. The literature search produced a total of 1708 studies. Of these, 1585 studies were excluded based on title and/or abstract review. A total of 123 articles remained for full-text review, 101 of which were subsequently excluded primarily because of lack of detailed information as to the reconstructive techniques used or clinical outcomes. Of the 22 studies remaining for final analysis, all were case series. A total of 673 patients were included in the analysis, with an overall postoperative CSF leak rate of 8.5%. Subgroup analysis was performed based on location of the skull base defect and presence and quality of intraoperative CSF leak. Conclusions. Based on level 4 evidence, in cases of low-flow intraoperative CSF leaks, skull base reconstruction with multilayered free grafts and synthetic materials offers similar outcomes to vascularized flaps. In cases of high-flow intraoperative CSF leaks, pedicled vascularized flaps appear to be superior. Location of the defect does not seem to be a significant factor in determining successful closure, with the exception of clival defects. In all other sites, good closure may be achieved by multiple reconstructive approaches. More consistency in data reporting and higher levels of evidence will ultimately be necessary to make definitive recommendations.

uring the past decade, indications for endoscopic endonasal surgery have expanded beyond inflammatory sinus conditions and now include treatment of sinonasal tumors, skull base lesions, and even intracranial pathology. As experience with expanded endoscopic endonasal approaches has increased, larger and more complicated resections are being undertaken, resulting in larger cranial base defects that pose surgical challenges for closure. As with any surgically created skull base defect, the need for effective reconstruction is paramount, both to separate the sinonasal and intracranial cavities and to avoid complications such as cerebrospinal fluid (CSF) leak, meningitis, and pneumocephalus. Initially, the choices of techniques and materials for the endoscopic closure of skull base defects were primarily based on experience gained from endoscopic CSF leak repair. But basic techniques such as free mucosal grafting were often insufficient for management of large skull base defects. With successful closure rates of less than 50% in some series, it subsequently became apparent that the inability to effectively reconstruct large skull base defects may have represented an Achilles heel of endoscopic skull base surgery. This concern prompted the development of more robust and durable reconstructive techniques, most notably the vascularized pedicled nasoseptal flap,1 which has offered excellent results and comparable outcomes to most open reconstructive techniques. Most would agree2 that the key factors to be considered when reconstructing an endoscopically created skull base defect are (1) the availability of tissues/materials for reconstruction, (2) location of the defect, (3) presence and flow

1 2

Keywords endoscopic skull base surgery, skull base reconstruction, CSF leak, skull base repair, high-flow CSF leak, low-flow CSF leak, systematic review

Stanford University School of Medicine, Stanford, California, USA Vanderbilt University School of Medicine, Nashville, Tennessee, USA

Corresponding Author: Peter H. Hwang, MD, Department of Otolaryngology–Head & Neck Surgery, Stanford University School of Medicine, 801 Welch Road, Stanford, CA 94305, USA. Email: [email protected]

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rate of intraoperative CSF leak, and (4) prior or future radiation therapy. The flow rate of intraoperative CSF leak is generally classified as low or high. Although there are no uniform criteria to determine the leak flow rate, it is generally accepted that a high flow leak exists when there is a direct communication between an arachnoid membrane defect and the brain cisterns or ventricles. In endoscopic skull base repair, the incidence of postoperative CSF leak is generally considered to be the most relevant primary outcome measure reflecting the success of skull base reconstruction. Numerous reconstructive techniques and materials have been reported in the literature. Most such publications describe heterogeneous cohorts, reporting various techniques of closure for multiple types of skull base defects. It is consequently difficult to make evidence-based decisions regarding which reconstructive techniques are best for specific types of skull base defects. Our objective was to review the best available evidence of closure techniques of endoscopically created skull base defects stratified by (1) the location of the skull base defect and (2) the flow rate of an intraoperative CSF leak. Thus, we aimed to develop an evidence-based algorithm for skull base reconstruction using postoperative CSF leak rate as the main outcome. As a secondary aim, we investigated the outcomes of related parameters, such as the use of routine postoperative lumbar drains (LD) and revision skull base repair for management of closure failures.

Materials and Methods A comprehensive systematic literature review was performed with the assistance of a library sciences specialist using the PubMed, SCOPUS, and Cochrane databases. The search was limited to articles published in the English language, and all nonhuman or cadaveric studies were excluded. All case reports and case series with less than 5 patients were also excluded from further analysis. Literature prior to January 2013 was searched using a dual-prong search algorithm designed to capitalize on MeSH terms, subheadings, and free text/keywords. The titles and abstracts of retrieved articles were reviewed, and appropriate studies were selected by 2 authors (E.S. and J.H.T.) in a standardized manner. All references cited by relevant captured review papers were also examined to ensure that all publications of interest were included. Full-text review was then performed by both authors to ensure that inclusion and exclusion criteria were met. To be included in the systematic review, studies had to include descriptions of (1) endoscopic endonasal skull base resection and (2) skull base reconstruction techniques and outcomes. Data pertaining to the location of the skull base defect as well as to the presence and quality of intraoperative CSF leak were also collected when available. Studies were excluded if they had a mixed case population from which individual outcomes could not be extracted, if the reconstruction techniques were poorly characterized, or if a technique was described in fewer than 4 patients. Studies that presented results on simple CSF leak or encephalocele repair were excluded as well.

Data were extracted from individual studies and entered into a standardized database. Clinical data included for subsequent analysis included patient age; follow-up time; location of skull base defect; quality of intraoperative CSF leak (high flow vs low flow), if present, as described by the authors; use of postoperative lumbar drains; presence of postoperative CSF leak; and management of repair failures. Successful closure of a skull base defect was defined as a surgical closure resulting in no postoperative CSF leak.

Assessment of Risk of Bias and Heterogeneity Assessment of risk of bias was conducted in accordance with the Agency for Healthcare Research and Quality Methods Guide for Comparative Effectiveness Reviews.3 The included studies were assessed for risk of bias based on the methods of data collection, sampling method, attrition (loss to followup of patients) and adequacy of reporting outcome. Judgment of the risk of bias for each study was categorized as ‘‘low risk,’’ ‘‘high risk,’’ or ‘‘unclear risk’’ of bias, as shown in Table 1. Evidence of high-risk bias or unclear bias in 1 or more of the above parameters was considered sufficient to change the bias category from low risk to high/unclear risk of bias. In addition, the risk of bias assessment was evaluated quantitatively using the Begg and Egger tests. Statistical analysis was performed using StatsDirect software version 2.7.9. Given the likelihood of between-study variability, a randomeffects model (DerSimonian-Laird) was employed, with heterogeneity assessed by the I2 statistic. Where possible, results are described in accordance with the PRISMA guidelines for reporting meta-analyses, with 95% confidence intervals reported throughout. A P value of \.05 was considered significant for all statistical tests.

Results The literature search produced a total of 1708 studies. Of these, 1585 studies were excluded based on title and/or abstract review. Most excluded studies were either review articles, single case reports, anatomic studies, studies describing CSF leak not associated with skull base surgery, studies describing nonendoscopic techniques, or duplicates. A total of 123 articles remained for full-text review, 101 of which were subsequently excluded primarily because of inadequate documentation of the reconstructive technique used or the absence of information pertaining to patient outcomes. Twenty-two studies4-25 were included in the final analysis. All included articles were case series, representing level 4 evidence. A total of 673 patients were extracted from the 22 studies for the outcomes analysis. The overall postoperative CSF leak rate after intraoperative skull base repair was 8.5% (57/673), revealing an overall success rate of 91.5% (95% confidence interval [CI] = 0.894137 to 0.935314; Figure 1).

Risk of Bias and Heterogeneity Assessment Qualitative assessment of the risk of bias is presented in Table 1, revealing a low risk of bias. In addition, both the Begg and Egger tests were nonsignificant (P = .22 and P = .34, respectively), corroborating the qualitative results. A

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Table 1. Qualitative Assessment for Risk of Bias. Authors

Year

Method of Data Collection

Carrabba et al4 Ceylan et al5 Garcia-Navarro et al6 Germani et al7 Harvey et al8 Horiguchi et al9 Kassam et al10 Kong et al11 Liu et al12 Luginbuhl et al13 Moliterno et al14 Muscatello et al15 Patel et al16 Shin et al17 Simal Julian et al18 Stippler et al19 Tabaee et al20 Villaret et al21 Zanation et al22 Rawal et al23 Saito et al24 Zhang et al25

2008 2011 2011 2007 2009 2010 2008 2011 2011 2010 2010 2011 2010 2011 2011 2009 2007 2010 2009 2012 2012 2012

Retrospective Retrospective Prospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Retrospective Prospective Retrospective Prospective Retrospective Retrospective Retrospective

Method of Sampling

Attrition (Loss to Follow-up)

Adequacy of Outcome Report

Consecutive Consecutive Consecutive Consecutive Consecutive Consecutive Consecutive Consecutive Unclear Consecutive Consecutive Consecutive Consecutive Consecutive Unclear Consecutive Consecutive Consecutive Consecutive Consecutive Consecutive Consecutive

None None None None None None None None None None None None None None None None None None None None None None

Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete Complete

funnel plot depicting this analysis is presented in Figure 2. Heterogeneity analysis revealed only a moderate heterogeneity between the studies’ I2 (inconsistency) = 42% (95% CI = 0% to 64.1%).

Outcomes Based on High- vs Low-Flow Intraoperative CSF Leak Twelve of the studies presented data on intraoperative CSF leak, 8 of which elaborated on the relationship between quality of flow and postoperative outcomes.6,11,13,14,18,20,22-24 Analysis of the pooled data from these studies revealed 3 subgroups: 141 patients with no evidence of intraoperative CSF leak, 74 patients with evidence of low-flow CSF leak, and 218 patients with high-flow CSF leak. In patients without evidence of intraoperative CSF leak, there were no postoperative leaks reported, regardless of the closure technique applied. Of the patients reported to have intraoperative CSF leak, persistent postoperative CSF leak occurred in 10.3% (30/292). We next analyzed the outcomes of the specific closure techniques presented for the subgroups that had evidence of intraoperative CSF leaks. For low-flow intraoperative CSF leaks, 5 studies presented data on 74 patients11,14,18,20,23 (Table 2). Successful closure was described for both nonvascularized and vascularized closure techniques. Reconstruction with layered free grafts was used in 64

Risk of Bias Low Low Low Low Low Low Low Low Unclear Low Low Low Low Low Unclear Low Low Low Low Low Low Low

patients, with an overall success rate of 92%.11,14,18 Reconstruction with a pedicled flap from the septum or middle turbinate was used in 10 patients with a 100% success rate. For high-flow intraoperative CSF leaks, 6 studies presented data on 218 patients. There appeared to be differences in success rates between vascularized versus nonvascularized closures, with specific techniques summarized in Table 3.6,11,13,18,20,22 Of the 218 patients, 107 patients were reconstructed with a vascularized pedicled flap with or without underlying free grafts, achieving a successful closure rate of 94%. The remaining 111 patients were reconstructed with multilayered free grafts without a pedicled flap, achieving a successful closure rate of only 82%. Notably, the lowest success rates were achieved when reconstruction was performed with an inlay of fat and Duragen and onlay of Duragen, resulting in a success rate of only 55% (11/20).13

Outcomes Based on Site of Skull Base Defect Fifteen studies, comprising a total of 313 patients, reported postoperative outcomes as a function of the location of the skull base defect being reconstructed (Table 4).4,5,7,12,14-16,18-25 We were able to stratify the site of the defect into 4 groups: (1) anterior cranial fossa (spanning locations from the planum sphenoidale to posterior frontal sinus table), (2) sellar defects, (3) tuberculum sellar defects, and (4) clival

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Figure 1. Forest plot for the success rate reconstruction of surgically created skull base defects.

Figure 2. Funnel plot assessing the risk of publication bias of success rate for reconstruction of surgically created skull base defects for each included study.

defects. In 7 studies, we were unable to extract accurate information pertaining to a specific defect location, and therefore, these studies were excluded from this analysis.

Anterior cranial base defects. Eight studies presented data on anterior cranial base reconstruction in a total of 142 patients, with an overall successful closure rate of 92% (Table 3). Successful closures were described with both nonvascularized and vascularized techniques, ranging from

single-layer free graft to multilayered closure including pedicled flap. In the series describing nonvascularized reconstruction, greater variance in success rates was observed. For example, a triple layer of iliotibial tract free tissue graft21 reconstruction achieved a 93% successful repair rate in a series of 41 patients. Yet in another smaller series of 6 patients in which a triple layer of fascia lata was also used, there was only a 67% success rate.15 No explanation for these poorer results was provided in the latter study; both studies reported a mixed population of low- and high-flow leaks, but specific characteristics about leak rates were not extractable from either study. The ‘‘gasket seal’’ technique of free graft closure was effective for high-flow leaks when used in conjunction with an inlaid free fat graft, with a success rate of 91%. However, the gasket seal technique was less successful when a communication with the ventricle precluded the use of inlaid fat; the success rate in a small group of 6 patients without fat graft inlay dropped to 67%. For anterior cranial base reconstructions using vascularized pedicled flaps, high rates of success were reported using both pedicled septal flaps and pedicled pericranial flaps. A repair technique using inlay of Duragen and an onlay of pedicled septal flap achieved excellent results with 96% success in 26 patients. A smaller series of 9 patients with Duragen inlay with pericranial flap onlay showed 100% successful closure. We attempted to assess the impact of high versus low CSF leak on the success rate of the various techniques described for anterior skull base reconstruction. No formal comparisons could be made due to inconsistencies in reporting. Of 7 total studies, 4 studies offered no information regarding intraoperative CSF leak. In one study, intraoperative CSF leak was documented but the quality of the intraoperative leak was not specified. Two studies focused on closure of documented high-flow CSF leak, whereas none of the studies presented data on low-flow intraoperative CSF leak.

Sellar defects. Five studies presented data on the reconstruction of sellar defects in a total of 104 patients. Reconstruction was described with biomaterials or with nonvascularized free grafts or with vascularized pedicled flaps with an overall successful closure rate of 93% (Table 3). Two studies presented outcomes of free graft/biomaterial reconstruction in the setting of low-flow intraoperative CSF leak. In one series, inlaid fat and bone/miniplate was used in 39 patients, achieving an 87% success rate. The other study, with only 10 patients, used gelfoam as inlay and polymethylmethacrylate as an onlay and reported a 100% success rate. No vascularized grafts or flaps were used in these patients.14 We found no data regarding free graft reconstruction of sellar high-flow leaks. Use of vascularized pedicled flaps was described in the other 3 studies with excellent (94%-100%) results, in both high- and low-flow intraoperative CSF leaks (Table 3).

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Table 2. Outcome of Specific Reconstruction Techniques for Cases of Low-flow Intraoperative CSF Leak. Technique

Number of Patients

Location of Defect

8 12 39 5 4 6

Clivus/sella/tuberculum/planum Clivus/sella/tuberculum/planum Sella Sella Sella Sella

Inlay, fat; onlay, mucosa graft11 Gasket seal 1 onlay of fascia lata11 Inlay, intradural fat; extradural, bone/miniplate20 Inlay, gelfoam; onlay, polymethylmethacrylate14 Onlay, middle turbinate flap18 Onlay, NSF23

Number of CSF Leaks % CSF Leaks 0 0 5 0 0 0

0 0 12.8 0 0 0

Abbreviation: CSF, cerebrospinal fluid; NSF, nasoseptal flap

Table 3. Outcome of Specific Reconstruction Techniques for Cases of High-flow Intraoperative CSF Leak. Technique Inlay, fat; onlay, mucosal graft11 Gasket seal 1 onlay of fascia lata11 Inlay, fat and Duragen; onlay, Duragen13 Gasket seal with inlay of fat20 Gasket seal (ventricular communication)20 Gasket seal6 Inlay, Duragen; onlay, NSF22 Inlay, fascia lata X2 (intra and extradural); onlay, NSF13 Onlay, middle turbinate flap18

Number of Patients

Location of Defect

9 17 20 34 6 25 66 16 4

Clivus/sella/tuberculum/planum Clivus/sella/tuberculum/planum Sella/tuberculum/planum ASB ASB Multiple, mainly sella and supra sella Sella/clivus/ASB Sella/tuberculum/planum Sella

Number of CSF Leaks % CSF Leaks 3 2 9 3 2 1 4 1 0

33 11.8 45 8.8 33 4 6 6.25 0

Abbreviation: ASB, anterior skull base; CSF, cerebrospinal fluid; NSF, nasoseptal flap.

Clival defects. Clival reconstruction was presented in 4 studies discussing a total of 51 patients with an overall successful closure rate of 80% (Table 3).4,19,22,24 In the only study presenting nonvascularized flap reconstruction, a 60% success rate was achieved with multilayer free grafts; the closure success rate improved to 100% when a pedicled septal flap was added as an onlay.4 In a small series of 4 patients that were a subset of a larger series, an inlay of fascia lata and onlay of septal flap achieved a 100% success rate.24 One institution published 2 series of clival chordoma patients repaired with an inlay of Duragen and an onlay of pedicled septal flap. In the first series, a 90% success rate was achieved in 10 patients22; however, in the second series, a larger cohort of 20 patients using the same reconstruction technique achieved a much lower success rate of 75%. In the latter study, a large number of the patients had previous radiation, recurrent tumors, or tumors with extensive intradural involvement.19 Intraoperative CSF leak was documented in 2 of the 4 studies. In one, a high-flow leak was present, and in the other, a mix of high- and low-flow leaks was present (Table 3). We were therefore unable to assess the impact of the flow of intraoperative CSF leak in these cases. Nonetheless, the above findings highlight the fact that reconstruction of clival defects with free grafts only is likely insufficient. Additional factors apart from the site and flow rate of CSF leak, such as prior radiation or recurrent

tumor, may affect the success rate of a specific repair technique.

Tuberculum defects. Reconstruction of tuberculum defects was discussed specifically in only 2 studies5,12 presenting a limited number of 22 patients with a 100% success rate. One described the use of free grafts and biomaterial for reconstruction and the other the use of a vascularized pedicled flap overlaying free tissue graft (Table 3). Since there was also no documentation of whether intraoperative CSF leak was present in this very limited data set, we were not able to assess the impact of this factor on the outcome of reconstruction.

Perioperative Lumbar Drainage Details regarding the use of perioperative LDs were presented in 12 of 22 studies, in a total of 474 patients.5,6,8-15,20,22 In these studies, 312 patients did not have perioperative lumbar drainage placed. Of these 312 patients, 144 had no intraoperative CSF leak, whereas 168 had some form of intraoperative leak: 31 patients with a low-flow leak, 27 patients with a high-flow leak, and 110 patients with unspecified low- or high-flow intraoperative leak (Table 5). A total of 172 patients had perioperative placement of LD, of whom 105 had a high-flow intraoperative CSF leak. In 59 patients, the intraoperative leak was not specified as either low or high flow (Table 5). In 8 patients, there was no mention

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Table 4. Outcome of Specific Reconstruction Techniques for Cases for Each Site of Skull Base Defect. Location

Vascularized vs Nonvascularized

Anterior skull base

Nonvascularized

Vascularized Sella

Nonvascularized Vascularized

Clivus

Nonvascularized Vascularized

Tuberculum

Nonvascularized Vascularized

Repair Technique

CSF Flow

Number of Patients

Success Rate (%)

Gasket seal with inlay of fat20 Gasket seal without inlay fat20 (ventricular communication) Inlay, fascia lata X2; onlay, FL15 Inlay, ITTx2; onlay, ITT21 Onlay of Alloderm7 Inlay, FL; onlay, muscle graft and Ethisorb Dural Patch25 Inlay, Duragen; Onlay, NSF22 Onlay, pericranial flap, Duragen16 Inlay, fat, bone/miniplate20 Inlay, gelfoam; onlay, polymethylmethacrylate14 Inlay, Duragen; onlay, NSF22 Onlay, middle turbinate flap18 Onlay, middle turbinate flap18 NSF onlay23 Inlay, Duragen, FL; onlay, FL4 Inlay, Duragen, FL; onlay, FL and NSF4 Inlay, Duragen; onlay, NSF19 Inlay, Duragen; onlay, NSF22 Inlay, FL; onlay, NSF24 Inlay, fat, FL; onlay, methylmethacrylate, free mucoperichondrium graft5 Inlay, FL; onlay, NSF12

H H M M NM NM H NM L L H L H L NM NM NM H M NM

34 6 6 41 12 8 26 9 39 11 34 4 4 6 10 7 20 10 4 8

91 67 67 93 100 88 96 100 87 100 94 100 100 100 60 100 75 90 100 100

NM

14

100

Abbreviations: CSF, cerebrospinal fluid; FL, fascia lata; H, high flow; ITT, iliotibial tract; L, low flow; M, mixed high and low flow; NM, not mentioned; NSF, nasoseptal flap; PMMC, polymethylmethacrylate.

Table 5. Analysis of Studies Describing of Skull Base Reconstruction in the Absence or Presence of Perioperative CSF Diversion via Lumbar Drain. Study Reference Harvey et al8 Horiguchi et al9 Kassam et al10 Kong et al11 Moliterno et al14 Muscatello et al15 Liu et al12 Tabaee et al20 Zanation et al22 Luginbuhl et al13 Rawal et al23 Ceylan et al5 Kong et al11 Luginbuhl et al13 Zanation et al22 Tabaee et al20 Garcia- Navarro et al6

CSF Diversion via Lumbar Drain

Number of Patients

Intraoperative CSF Leak Flow

No No No No No No No No No No No Yes Yes Yes Yes Yes Yes

25 21 20 98 11 6 14 84 5 22 6 8 26 14 65 28 31

N/A 7, none; 14, yes None 78, none; 20, low flow 6, none; 5, low flow N/A N/A 33, none; 51, high or low flow High flow All high flow Low flow N/A High flow High flow High flow Low and high flow Low and high flow

Abbreviations: CSF, cerebrospinal fluid; N/A, not available. Downloaded from oto.sagepub.com at PRINCETON UNIV LIBRARY on August 28, 2014

Number of Postoperative CSF Leaks 1 2 0 0 0 2 0 Cannot determine 0 Cannot determine 0 0 5 Cannot determine 4 Cannot determine Cannot determine

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of either the presence or quality of intraoperative CSF leak. Most of the above studies did not specify the outcome of a specific reconstruction technique with regard to the use of perioperative LD. We were therefore not able to evaluate whether placement of LD affected the outcome of skull base reconstruction, particularly in cases of intraoperative high-flow CSF leaks.

Management of Unsuccessful Skull Base Reconstructions In 57 (of 673) patients, primary skull base reconstruction resulted in a persistent postoperative CSF leak, and a secondary intervention was required. These data were available for only 42 patients. Postoperative CSF leak was successfully managed by lumbar drainage alone in 16 patients (38%) and by revision of the skull base repair, with or without LD placement, in 26 patients (62%). We could not determine from the data available which factors predicted successful management by postoperative LD alone versus those that would require revision surgery.

Discussion A wide range of reconstructive techniques has been used in endoscopic skull base surgery, including various combinations of free tissue grafts and biomaterials. With recent advances in the development of vascularized regional flaps that can be raised endoscopically, vascularized flaps have been increasingly employed for skull base closure as well. Most techniques appear to be effective at closing active CSF leaks, with our systematic review data showing an overall success rate of 92%. Interestingly, success rates remained high (90%) when only cases with intraoperative CSF leak were included in the analysis, emphasizing the recent advancements in skull base reconstruction. A recent systematic review of reconstruction of large dural defects26 found that vascularized flaps were associated with a lower rate of postoperative CSF leaks when compared with free tissue grafts. However, it has not been delineated when a vascularized flap is indicated versus when a simple free graft and/or biosynthetic material may suffice. In this study, we attempted to use evidence-based data to define the indications for various techniques for the reconstruction of endoscopically created skull base defects. All studies identified in our systematic review were case series with small groups of patients (level 4 evidence). There have been no published randomized control studies, cohort studies, or case-control studies to date, thus limiting the findings of the current study to grade C recommendations. The data are also limited by a lack of standardized descriptions of skull base defects and their repair, which affects the comparability of various defect types and closure techniques. Our results should therefore be interpreted with appropriate caution. In addition, since studies with fewer than 5 patients were excluded from our review, recent reports detailing the successful reconstruction of skull base defects with inferior

turbinate flaps, palatal flaps, and temporoparietal fascia flaps27-30 were not analyzed. We focused on 2 main factors: the location of the skull base defect and the degree of intraoperative CSF flow. Independent analysis of these factors individually was difficult, primarily because of the potential interdependence of the criteria, with certain locations of the skull base more characteristically associated with higher or lower flow leaks. When we compared reconstruction outcomes by subsite of defect, there were no clear differences between vascularized versus nonvascularized reconstruction techniques for any individual subsite apart from the clivus. Free tissue grafts, biomaterials, and vascularized pedicled flaps were all successfully used in reconstructing defects. Better results of clival defect reconstruction were achieved with pedicled vascularized flaps. It appears that specific characteristics of the defect may be more relevant to selection of reconstructive technique, rather than the anatomic subsite. For example, in anterior cranial base defects, it is thought that the weight of the brain on an inlay graft helps to hold the material in position securely and prevent migration.7 In contrast, the tuberculum sella and the clivus are anatomically closer to the anterior brain cisterns and ventricles. Resection of lesions in these areas is therefore at higher risk of resulting in high-flow CSF leaks, and hence, the lesions may probably benefit more from vascularized flap reconstruction. When data regarding the quality of intraoperative CSF leak were also taken into consideration, differences in success rates were noticed for high-flow leaks; for any given subsite, higher flow leaks were repaired with greater success rates when vascularized tissue was used. Because of the heterogeneity of data reporting, analysis of reconstruction outcomes in low-flow intraoperative CSF leak was limited to studies of defects of the sellar and parasellar regions. Data on high-flow intraoperative CSF leak were present for all subsites. The analysis revealed that in low-flow intraoperative CSF leaks, layered repair with various types of free grafts and/or synthetic materials appeared to result in excellent (92%) outcomes. In cases of high-flow intraoperative CSF leak, the addition of vascularized pedicled flaps resulted in improved rates (94% vs 82%) of successful skull base closure. Similar conclusions were reported by Patel et al,2 who reviewed endoscopic skull base reconstruction techniques. The generalizability of these results should be interpreted with caution since they are based on a limited number of studies. In cases in which no intraoperative CSF flow was noted, the outcomes were excellent regardless of whether the cranial base defect was repaired or not. Other factors that may influence the outcome of cranial base reconstruction were insufficiently presented in the case series analyzed and therefore could not be included in the analysis. These factors included the size of the cranial base defect, prior history of radiation therapy, and the presence or absence of a bony rim around the defect. As a matter of expert opinion, many authors would agree that patients with larger defects and those receiving radiation therapy would probably benefit from a vascularized flap to promote better

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wound closure.10 In addition, where no bony ledges are present around a defect, the use of the ‘‘gasket seal’’ method or of Alloderm alone, both of which necessitate tucking of free grafts under bony ledges, may be less optimal. However, these recommendations are not currently substantiated by evidence higher than level 5. The indications for placement of LD in endoscopic skull base surgery are poorly defined, and routine placement of perioperative lumbar drains is considered by many skull base surgeons to be unnecessary. This is mainly based on previous reports assessing the value of LD placement in spontaneous and traumatic CSF leak repairs, in which the success rate of CSF leak repair was unchanged whether LD was placed or not.31,32 Moreover, analysis of the risk/benefit ratio of LD use for endoscopic skull base surgery has shown that complications of LD may be more frequent than those of postoperative CSF leaks themselves.33 The value of LD placement in patients with intraoperative CSF leak, particularly high-flow leaks, could not be definitively determined from the systematic review due to heterogeneity of data reporting. For example, the frequency of lumbar drain placement was reported in only two-thirds of eligible studies, and the indications for LD placement were not specified in most cases. In general, perioperative lumbar drains were placed in those patients with evidence of intraoperative high-flow CSF leaks. However, not all patients with high-flow intraoperative CSF leaks had perioperative LDs placed, and successful closure of high-flow leaks without LD was also reported. The reporting of successful closure of high-flow CSF leaks without LD suggests that LDs are probably not essential in all patients with highflow intraoperative CSF leak. A recent study supports this finding and suggests that the use of routine postoperative CSF diversion for management of high-flow CSF leaks created during endoscopic skull base surgery may not be necessary when a septal flap is used.34 With level 4 evidence supporting both the use and nonuse of LD in high-flow leaks, no definitive conclusions could be made. The most consistent indication reported for LD placement was for the management of postop failures of skull base reconstruction. In 40% of cases of failed reconstruction in which no LD had been placed intraoperatively, LD placement postperatively led to satisfactory resolution of the CSF leak; 60% of reconstruction failures required revision surgery. This level 4 evidence suggests that placement of a lumbar drain may be indicated as a first-line treatment for persistent postop CSF leak, while in cases in which an LD has already been placed, immediate revision of the reconstruction may be necessary. Additional studies with more comprehensive reporting and stratification of predictive factors may help to develop more definitive indications for LD use in endoscopic skull base surgery.

Conclusions Based on level 4 evidence, in cases of low-flow intraoperative CSF leaks, skull base reconstruction with multilayered free grafts and biosynthetic materials offers similar

outcomes to vascularized flaps. In cases of high-flow intraoperative CSF leaks, pedicled vascularized flaps appear to be superior. Location of the defect does not seem to be a significant factor in determining successful closure, with the exception of clival defects. In all other sites, good closure may be achieved by multiple reconstructive approaches. The value of intraoperative lumbar drain placement is indeterminate; however, postoperative lumbar drain placement is indicated as initial management of postoperative CSF leaks, with revision surgery reserved for cases of lumbar drain failure. More consistency in data reporting and higher levels of evidence will ultimately be necessary to make definitive recommendations as to the optimal reconstruction techniques for specific types of endoscopically created skull base defects. Acknowledgment The authors would like to acknowledge the contributions of Christopher Stave from the Stanford University School of Medicine Lane Medical Library for his assistance with the systematic literature review.

Author Contributions Ethan Soudry, conception, design, acquisition of data, analysis, drafting, final approval; Justin H. Turner, acquisition of data, drafting, approval; Jayakar V. Nayak, interpretation of data, drafting, approval; Peter H. Hwang, conception, analysis and interpretation of data, drafting, approval.

Disclosures Competing interests: Jayakar V. Nayak, Medtronic, Stryker Navigation, Olympus, consultant; Polyganics, scientific advisory board (no relevant conflicts with the article); Peter H. Hwang, Medtronic, Sinuwave, Intersect, 3NT, consultant (no relevant conflicts with the article). Sponsorships: None. Funding source: None.

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