Impact of Obesity on Postoperative Complications after Lateral Skull Base Surgery: A Systematic Review

The population of overweight (body mass index [BMI] ≥25) and obese (BMI ≥30) individuals continues to rise and has reached epidemic levels in the USA, with an estimated prevalence of approximately 42% among US adults [1]. The health impact of obesity is drastic. For every increase in 5 kg/m² over a BMI of 25, overall mortality, vascular mortality, and diabetes-related mortality increase by 29%, 41%, and 210%, respectively [2]. Obesity-related morbidity and mortality are comparable with those of cigarette smoking, the leading cause of preventable death in the USA. However, while smoking rates in the USA have decreased from 20.9% in 2005 to 13.7% in 2018, the percentage of obese individuals continues to increase [3, 4].

Elevated BMI adversely impacts perioperative outcomes in several surgical subspecialties [5‒9]. However, results are inconsistent across the literature, with some studies finding no association between obesity and surgical complications [10‒13]. Otolaryngology is no exception to these trends. It is well established that obese patients have an increased risk of several otolaryngologic diseases, including obstructive sleep apnea, idiopathic intracranial hypertension, and spontaneous cerebrospinal fluid (CSF) leak [7, 8]. More recently, obesity has been associated with an increased risk of hearing loss and chronic rhinosinusitis [14, 15]. However, the impact of obesity on perioperative outcomes is not clear across all areas of Otolaryngology. Some studies have found no effect of obesity on postoperative outcomes after head and neck free tissue transfer [13], while others have shown a protective effect on oncologic outcomes in patients with head and neck squamous cell carcinoma [12].

The relationship between obesity and complications after lateral skull base tumor resection is unclear. There is conflicting evidence regarding the incidence of postoperative complications in this patient population. The purpose of this study is to examine the relationship between obesity and outcomes following lateral skull base tumor resection, including postoperative complications such as CSF leaks, readmission rates, reoperation rates, and length of stay (LOS).

A comprehensive search of the MEDLINE (PubMed), Embase (Elsevier), CINAHL (EBSCO), and Cochrane CENTRAL (Wiley) databases in February 2021 was performed. The search strategy was comprised of two main concepts: obesity and lateral skull base and included key words and database-specific terminology (e.g. MeSH). Search terms were structured to capture patients undergoing transtemporal approaches to the posterior fossa, including the internal auditory canal, or posterior or middle fossa approaches to the temporal bone. The full strategy is presented in Supplemental Figure 1 (for all online suppl. material, see https://doi.org/10.1159/000531531). No restrictions were placed upon language or date of publication. A total of 1,251 references were identified across databases and imported into Covidence systematic review management software. Covidence identified 342 duplicate records, leaving 909 abstracts to screen. The final cohort included all adult patients who underwent lateral skull base tumor removal. Only abstracts that studied the relationship between overweight or obese status and postoperative outcomes following lateral skull base tumor resection were included. 25 abstracts underwent full-text review, with 14 full-text manuscripts meeting final inclusion criteria (Fig. 1). Exclusion criteria were studies with fewer than 5 patients, pediatric patients, non-English texts, and secondary studies such as systematic reviews and meta-analyses. For studies performed by the same author group that included duplicate patient populations, the most recent study was included for analysis.

Data extraction was divided among two reviewers. Extracted data included study information, patient demographics, tumor pathology, surgical approach, and postoperative outcomes including incidence of CSF leak, LOS, reoperations, readmissions, and operative time. Descriptive statistics were used to compare postoperative outcomes for obese and nonobese controls. Due to both clinical and methodological heterogeneity of the studies, cumulative results were not pooled into a meta-analysis. The Newcastle-Ottawa scale was used to perform quality assessment. Two authors independently scored each study, and a consensus score was reached for any disagreements. Results of bias assessment are found in Table 1.

All 14 studies were retrospective analyses with publication dates ranging from 2009 to 2020. The cumulative number of patients was 15,928 (Table 1). Nine studies evaluated the relationship between obesity and postoperative CSF leaks [16‒18, 22‒26, 29]. Six studies described the relationship between obesity and postoperative LOS [19, 20, 22, 24, 26, 28]. Five papers studied the influence of obesity on readmission and reoperation rates [20, 21, 24, 25, 27]. Two studies compared operative time between obese and nonobese patients [20, 25]. Tumor types encompassed across studies included vestibular schwannoma, meningioma, glomus vagale, facial neuroma, epidermoid cyst, trigeminal neuroma, glomus jugulare, arachnoid cyst, and choristoma.

Nine studies compared the incidence of postoperative CSF leak after lateral skull base tumor resection between obese and nonobese patients [16‒18, 22‒26, 29] (Table 2, Table 3). The cumulative leak rate was 3.8% across all studies.

Four studies found a significant association between obesity and postoperative CSF leaks [16, 18, 25, 26]. Alattar et al. [16] performed a retrospective analysis to identify risk factors for 30-day readmission due to CSF leak following vestibular schwannoma (VS) surgery using a statewide database. This study found that 240 out of 6,820 (3.5%) patients developed a postoperative CSF leak. Overweight or obese status on admission was significantly associated with the risk of 30-day readmission for CSF leak (OR 2.10, 95% CI: [1.20–3.66], p = 0.009). In a retrospective review of 362 patients diagnosed with vestibular schwannomas, Luryi et al. [25] compared postoperative outcomes between obese and nonobese controls. A BMI greater than 30 was independently associated with postoperative CSF leak (OR 1.11, 95% CI: [1.04–1.18], p = 0.002). Similarly, Mantravadi et al. [26] studied the relationship between BMI and postoperative complications after transtemporal cerebellopontine angle (CPA) surgery. In this study, 15 out of 134 patients (11.1%) developed a postoperative CSF leak. Average BMI in the CSF leak cohort was 34.03 compared to 27.09 in the non-CSF leak group (OR 1.13, 95% CI: [1.03–1.18], p = 0.004). In a study of 457 patients that underwent VS resection, Copeland et al. [18] found BMI to be significantly associated with CSF leak (OR 1.06, 95% CI: [1.01–1.10], p = 0.01) [18]. 45 out of 457 (9.8%) patients developed postoperative CSF leaks, 87% of which were in overweight or obese individuals.

In contrast, five studies found no significant association between elevated BMI and postoperative CSF leak [17, 22‒24, 29]. A retrospective study of 170 patients with CPA tumors found no difference in the average BMI between patients who developed a postoperative CSF leak versus those who did not (27.63 vs. 26.75) [17]. Hatch et al. reported similar outcomes in a national database study of patients who underwent vestibular schwannoma surgery between 2012 and 2015 [22]. Lipschitz et al. [23] studied the incidence of postoperative CSF leak after the middle cranial fossa approach to VS resection. Two out of 66 patients (3.0%) developed a CSF leak, and BMI did not significantly influence this outcome (p = 0.30). In a similar study using the translabyrinthine approach to VS resection, incidence of CSF leak was 12% (N = 33/275), with no difference in BMI between those who did or did not develop a CSF leak [29]. Finally, Lipschitz et al. [24] also studied whether elevated BMI was associated with postoperative complications after VS surgery using all surgical approaches. Postoperative CSF leak developed in 22 out of 205 patients (10.7%), nine of whom were obese. Obesity, defined as a BMI of 30 or higher, was not associated with postoperative CSF leak on univariate analysis (p = 0.82).

Out of six studies that assessed the influence of BMI on LOS, only one found an association (Table 4). O’Connell et al. [28] studied predictors of LOS in patients undergoing lateral skull base surgery for benign cranial nerve lesions using the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) databases. 252 patients were identified from 2009 to 2012. Patients with a BMI ≥30 had a significantly longer LOS compared to patients who were not obese (5.6 ± 3.9 d vs. 4.6 ± 3.4 d, p = 0.006). Obesity as well as operative time and reoperation within 30 days were independent predictors of a prolonged LOS on multivariate analysis.

The remaining five studies did not elicit a relationship between elevated BMI and prolonged LOS [19, 20, 22, 24, 26], with one study finding elevated BMI to be a protective factor for shorter hospital stays [19]. In a retrospective study of 401 patients that underwent vestibular schwannoma resection, a higher BMI was protective for LOS on linear regression analysis (β= −0.06, p < 0.044) [19]. Goshtasbi et al. [20] used the NSQIP database from 2005 to 2017 to evaluate surgical morbidity after vestibular schwannoma in an obese versus nonobese cohort. LOS was slightly longer in the obese (BMI ≥30) cohort (5.2 ± 4.2 vs. 4.9 ± 3.9); however, this did not reach statistical significance (p = 0.11). Another national database study of vestibular schwannoma surgical patients utilizing the University Health System Consortium (UHC) inpatient database from 2012 to 2015 also found no association between obesity and prolonged LOS (p = 0.23) [22]. In the study by Lipschitz et al., obese patients and nonobese patients had similar hospital stays (4.5 vs. 4.4, p = 0.88) [24]. Similarly, Mantravadi et al. [26] found no difference in BMI between patients that had a hospital stay greater than 3 days and those that did not (29.10 vs. 28.20, p = 0.49).

Four studies evaluated the relationship between obesity and both readmission and reoperation rates [20, 21, 24, 27], and one studied obesity and reoperation rates alone [25] (Table 5, Table 6). In the study by Goshtasbi et al. [25] of 1,405 vestibular schwannoma patients, 30-day readmission and reoperation rates were 9.3% and 7.5%, respectively. These rates did not differ between an obese (BMI ≥30) and nonobese cohort. Lipschitz et al. [20] had a readmission rate of 12.7% and a reoperation rate of 4.9% in their study of vestibular schwannoma patients. The readmission rate did not differ between obese and nonobese patients. There was a trend toward an increased reoperation rate in patients with a BMI of 30 kg/m² or higher compared to nonobese controls (N = 6, 60% of reoperations vs. N = 4, 40% of reoperations); however, this did not reach statistical significance (p = 0.19).

Murphy et al. [27] performed a study of all patients with a benign cranial nerve neoplasm using ACS-NSQIP from 2007 to 2013. Postoperative morbidity, readmission, and reoperation rates were analyzed based on patient BMI. Thirty-day readmission did not differ based on patient BMI on bivariate analysis (p = 0.488). Return to the operating room trended toward a higher rate based on increasing BMI; however, this did not reach statistical significance (p = 0.323). However, on multivariate analysis, return to the operating room was significantly higher in patients with a BMI ≥40 (OR 6.25, 95% CI: [1.27–30.37], p = 0.024). Gupta et al. [21] performed a similar study of all patients with benign cranial nerve neoplasms using ACS-NSQIP from 2011 to 2015. Out of 996 patients, 108 (10.8%) and 80 (8.0%) were readmitted or underwent a second operation, respectively. The rates of readmission and reoperation did not differ based on BMI.

Finally, Luryi et al. [25] analyzed reoperation rates between obese (BMI ≥30) and nonobese (BMI <30) patients undergoing surgery for vestibular schwannomas. Reoperation was defined as the need for any revision surgery within 6 months postoperatively and not exclusively for removal of residual tumor. The overall reoperation rate was 9.1% (N = 33). Of these 33 patients, 19 (57.6%) were obese and 14 (42.4%) were nonobese. The increased rate of reoperation in obese patients reached statistical significance on multivariate analysis (OR 1.07, 95% CI: [1.01–1.13], p = 0.02).

Other analyzed outcomes reported in multiple studies included operative time. Two studies compared operative time between obese and nonobese patients. Goshtasbi et al. [20] found a slightly higher average operative time in obese (BMI ≥30) patients compared to nonobese patients (413.4 +/− 168 vs. 401.4 +/− 157 min); however, this was not statistically significant (p = 0.17). Luryi et al. [25] also evaluated operative time based on BMI and found no significant difference in BMI between patients with an operative time greater than 6 h versus less than 6 h.

The current literature on the relationship between obesity and postoperative outcomes after lateral skull base tumor removal is inconclusive. This review suggests a trend toward an increased risk of postoperative CSF leak in obese patients undergoing lateral skull base tumor resection, with a CSF leak rate ranging from 2.1 to 15.9%. However, the results do not show a clear association between elevated BMI and postoperative LOS, readmission rates, reoperation rates, or operative time.

Postoperative CSF leak is a known complication after resection of lateral skull base tumors [16]. There is an established relationship between elevated BMI, spontaneous CSF leaks, and idiopathic intracranial hypertension in non-surgical patients. Obese patients account for approximately 80% of the spontaneous CSF leak patient population [25, 30]. Likewise, recent literature has reported an increased risk of postoperative CSF leak in overweight and obese patients both in anterior and lateral skull base surgery [16, 18, 25, 26, 31]. Postoperative CSF leak increases the risk of meningitis and reoperation and prolongs hospital stay. As such, identifying potential risk factors is essential both when identifying optimal surgical candidates and counseling patients.

In this review of the current literature, the incidence of postoperative CSF leak was ranged from 2.1 to 15.9% [16‒18, 22‒26, 29]. Our results point toward an increased incidence of postoperative CSF leak in the overweight and obese population with four studies reaching statistical significance [16, 18, 25, 26] and three studies [17, 23, 29] with a higher rate of CSF leak in obese patients that was not statistically significant. Conversely, one study found no significant difference in CSF leak rate between obese and nonobese groups, with a slightly higher percentage of CSF leaks in the nonobese group [24].

This study also found no increased risk of postoperative complications in the obese patient cohort. The authors of the aforementioned study note that the explanation for these results is not immediately evident and partially attribute their findings to the “obesity-paradox,” wherein overweight and moderately obese patients experience a paradoxically lower rate of some postoperative complications compared to their underweight or morbidly obese counterparts. Although the exact mechanism is not understood, it is suggested that excess metabolic and nutrient reserves in obesity trigger a chronic, low-grade inflammatory state. This inflammatory state triggers the same signaling pathways induced by tissue injury and repair processes. Thus, obese patients may have developed an adaptive mechanism needed to mount an appropriate inflammatory and immune response to the stressors of surgery [32].

Heterogeneity in study design limits the strength of conclusions that can be drawn. Two studies were based on statewide or national databases and were limited in their description of patient characteristics and surgical details, whereas the remaining seven studies were retrospective analyses [16, 22]. Notably, two studies, Alattar et al. and Copeland et al., included overweight with obese patients, which may confound the significance of their results [16, 18].

Six studies included in this review evaluated the impact of obesity on postoperative LOS [19, 20, 22, 24, 26, 28]. Only one study demonstrated that obesity was associated with a longer LOS using the ACS-NSQIP database [26]. The authors attribute this to several factors, including delayed postoperative mobilization, increased risk of postoperative CSF leak, and increased postoperative complications. However, the ACS-NSQIP database lacks several patient and disease-specific characteristics, thus limiting a comprehensive analysis of all factors that may have prolonged postoperative LOS.

In contrast, the remaining studies found no association between elevated BMI and prolonged postoperative LOS. While increased BMI is known to increase the risk of several medical conditions including cardiopulmonary-related conditions, its effects on postoperative complications are less well-defined. Lipschitz and colleagues found that obesity was not associated with most postoperative complications after vestibular schwannoma resection, including length of hospital stay [24]. Goshtasbi et al. [20] found similar results and also observed that while postoperative myocardial infarction and wound complications were more common in the obese patient cohort, LOS and other complication rates were similar to the nonobese cohort. Interestingly, Dang et al. [19] found BMI to have a potentially protective impact on LOS, which again could be explained in part by the obesity-paradox, though the mechanism underlying this phenomenon is still poorly understood.

The effect of obesity on readmission and reoperation rates in other surgical fields is inconclusive [33‒35]. This review yielded similar results. Three studies evaluated the impact of obesity on 30-day readmission and/or reoperation using the ACS-NSQIP database [20, 21, 27]. All three studies utilized the same ICD-9/ICD-10 codes (225.1/D33.3) over different time periods, collectively spanning from 2005 to 2017. Of these three studies, only Murphy et al. [27] found that reoperation rates were higher in morbidly obese patients with a BMI ≥40. Gupta found a trend toward an increased readmission and reoperation rate for obese patients; however, this did not reach statistical significance [21]. In contrast, Goshtasbi found a higher rate of readmission and reoperation in the nonobese cohort compared to the obese cohort, with low overall postoperative complications in the obese population [20]. It is worth noting that Goshtasbi et al. [20] narrowed their search to only those patients with benign cranial nerve neoplasms that underwent an infratemporal, transtemporal, middle/posterior fossa, or posterior fossa approach. In contrast, the other two studies included all benign cranial nerve neoplasms based on ICD-9 code 225.1 [21, 27]. Based on the ICD-9 classification, “acoustic neuroma” and/or “vestibular schwannoma” are categorized under the umbrella term “benign cranial nerve neoplasms.” Murphy et al. [27] state, however, that because of the rare occurrence of other benign neoplasms of cranial nerves, the assumption that the vast majority of cases represent vestibular schwannoma is reasonable. Similarly, Gupta et al. state that while surgical approach may vary based on the origin of the schwannoma, most neoplasms included in their study likely represent vestibular schwannoma which undergo lateral skull base approaches. The authors’ note that a surgical approach was not included in their coding strategy due to inconsistencies in national coding practices for vestibular schwannoma [21]. As a result of the aforementioned assumptions made by both authors, both studies were included in this review. Nonetheless, the possibility that a small percentage of patients included in these studies may represent cranial nerve lesions that were not managed via a lateral skull base approach limits the conclusions that can be drawn based on their results.

Additionally, Lipschitz and Luryi assessed the impact of obesity on readmission and/or reoperation in their retrospective analyses [24, 25]. Lipschitz et al. [24] found no difference in 30-day readmission or any return to the operating room between an obese (BMI ≥30) and nonobese (BMI ≤30) cohort. In contrast, Luryi et al. [25] found a higher need for revision surgery within 6 months postoperatively in those with a BMI ≥30; however, this was attributed to the 7-fold increase in postoperative CSF leak in this patient population.

These inconclusive results can be attributed to several factors. Some of the data could be biased if there was differential employment of intraoperative or postoperative lumbar drainage. Furthermore, if patients had a postoperative CSF leak that was diagnosed before discharge and resolved with a lumbar drain without need for reoperation, they would not be identified with an analysis of readmission and reoperation rates. Except for the morbidly obese patient population, the impact of obesity on readmission and reoperation after lateral skull base tumor resection is not evident.

Two studies evaluated whether obesity prolongs duration of surgery and found no association between elevated BMI and operative time [20, 25]. It is worth noting the differences in the definition of surgical duration in both papers. The ACS-NSQIP database used by Goshtasbi et al. [20] defines operative time as skin incision to skin closure time. Luryi et al. [25] documented operative time as the duration of intraoperative neuromonitoring in their retrospective analysis. Due to the nature of lateral skull base surgery, one might expect similar skin-to-skin operative times in obese and nonobese patients. Surgical access to the CPA does not require significant soft tissue division, and the bony anatomy of the skull base is largely conserved regardless of body habitus [25]. In contrast, it is likely that the obese patient population has a longer operative time when considering the amount of time that lapses from when a patient enters and exits the operating room. Obesity is an independent predictor of a difficult airway, both in terms of difficult bag-mask ventilation and endotracheal intubation, which can prolong induction of anesthesia [36]. Additionally, patient positioning presents several challenges and can further prolong surgical duration. The aforementioned studies do not account for such challenges, and as such, further studies are needed to determine the effect of elevated BMI on total operative duration for lateral skull base tumor surgery [25, 19].

This study is not without limitations. First, all included studies are retrospective in nature and are subject to biases inherent to this study type. Additionally, several studies were based on statewide or national databases. National databases have intrinsic limitations. Limited data is available for tumor size, surgical approach, and postoperative outcomes including CSF leak and nerve injury, all of which may affect our outcomes. The ACS-NSQIP database only assesses 30-day complications, including readmission and reoperation rates. Consequently, long-term complications were unable to be assessed in these studies. Our study is also limited by the possibility of duplicate patient populations. Several studies utilized the ACS-NSQIP database over various, overlapping time frames and may capture a portion of the same patient population. As such, postoperative outcomes may differ from what is reported in this study and limits the quality of our evidence. However, because the studies included different time frames and evaluated various outcomes, we believe that the most comprehensive method was to include all papers as they were relevant to this study.

This study also has outcome-level limitations. There was heterogeneity both in study design and definition of clinical outcomes. As a result, we were unable to pool the data into a meta-analysis. Further, our study is limited by the potential for different postoperative morbidities depending on which approach is taken to the lateral skull base. The studies varied in the proportion of patients that had a retrosigmoid, translabyrinthine, middle cranial fossa, or other approaches to their tumors, and information regarding choice of approach was not available for all included studies. Consequently, we cannot draw conclusions about the differences in postoperative outcomes between the various surgical approaches. Lastly, two studies included all patients with benign cranial nerve neoplasms based on a national database and, as such, may have captured some patients that did not have lateral skull base tumors [21, 27]. However, as previously mentioned, the authors of the aforementioned studies made the assumption that the vast majority of the patients identified by their coding strategy had vestibular schwannomas, given the rare occurrence of schwannomas arising from other cranial nerves. Both studies, however, found no significant association between obesity and readmission or reoperation rates aside from a slightly higher reoperation rate in the morbidly obese population in the study by Murphy et al. [27]. As a result, we feel the inclusion of these studies does not significantly impact our results, despite the possibility that there is a small percentage of patients that represent schwannomas that were not managed via a lateral skull base approach.

Nonetheless, this study is the first comprehensive review that evaluates the relationship between obesity and complications after lateral skull base tumor resection. These limitations underscore and highlight the importance and need for more systematic research into the impact of obesity on patients undergoing lateral skull base procedures.

Our results indicate that current published data do not suggest that obesity increases postoperative LOS, readmission, or reoperation rates after lateral skull base tumor resection. The relationship between obesity and postoperative CSF leak is inconclusive but has trended toward an increased incidence of postoperative CSF leak in the obese patient population. Obese patients should be counseled about this risk prior to tumor removal and the consequent increased risk of meningitis, reoperation, and prolonged hospitalization. Obesity is an increasingly prevalent problem with numerous potential implications, and more studies should be done to clarify its impact on patients undergoing lateral skull base procedures.

An ethics statement is not applicable because this study is based exclusively on published literature.

The authors have no conflicts of interest to declare.

This article did not receive funding.

Study design, data analysis and collection, drafting of the manuscript, and final approval of the manuscript: Bridgham, Shikara, Ludeman, Eisenman. This work was presented at the American Neurotological Society at COSM on April 29–31st in Dallas, TX.

All data generated or analyzed during the study are included in this article. Further inquiries can be directed to the corresponding author.