Going the Distance in Acoustic Neuroma Resection: Microsurgical Outcomes at High-Volume Centers of Excellence

doi:10.21203/rs.3.rs-2579737/v1

Purpose: High-volume hospitals are associated with improved surgical outcomes for acoustic neuromas (ANs). Due to the benign and slow-growing nature of ANs, many patients travel to geographically distant cities, states, or countries for their treatment. However, the impact of travel burden to high-volume centers, as well as its relative benefit are poorly understood. We compared post-operative outcomes between AN patients that underwent treatment at local, low-volume hospitals with those that traveled long distances to high-volume hospitals.

Methods: The National Cancer Database was used to analyze AN patients that underwent surgery (2004–2015). Patients in the lowest quartile of travel distance and volume (Short-travel/Low-Volume: STLV) were compared to patients in the highest quartile of travel distance and volume (Long-travel/High-Volume: LTHV). Only STLV and LTHV cases were included for analysis.

Results: Of 13,370 cases, 2,408 met inclusion criteria. STLV patients (n = 1,305) traveled a median of 6 miles (Interquartile range [IQR] 3-9) to low-volume centers (median 2, IQR 1-3 annual cases) and LTHV patients (n = 1,103) traveled a median of 143 miles [IQR 103-230, maximum 4,797] to high-volume centers (median 34, IQR 28–42 annual cases). LTHV patients had lower Charlson/Deyo scores (p=0.001), mostly received care at academic centers (81.7% vs 39.4%, p<0.001), and were less likely to be minorities (7.0% vs 24.2%, p<0.001) or underinsured (4.2% vs 13.8%, p<0.001). There was no difference in average tumor size.

On multivariable analysis, LTHV predicted increased likelihood of gross total resection (odds ratio [OR] 5.6, 95% confidence interval [CI] 3.8-8.4, p<0.001), longer duration between diagnosis and surgery (OR 1.3, 95% CI 1.0-1.6, p=0.040), decreased length of hospital stay (OR 0.5, 95% CI 0.4-0.7, p<0.001), and greater overall survival (Hazard Ratio [HR] 0.6, 95% CI 0.4-0.95, p=0.029). There was no significant difference in 30-day readmission on adjusted analysis.

Conclusion: Although traveling farther to high-volume centers increased the time between diagnosis and treatment for AN patients, they experienced superior postoperative outcomes compared to patients who received treatment locally at low-volume centers. Enabling access and travel to high-volume centers may improve AN patient outcomes.

acoustic neuroma

vestibular schwannoma

surgeon volume

hospital volume

outcomes

mortality

Acoustic neuromas (ANs) are benign nerve sheath tumors of the vestibular nerve, occurring in approximately 1 in 100,000 people. Treatment options include observation, radiation, and microsurgical resection. Improved outcomes have been observed after surgery for ANs at high-volume surgical centers, with lower morbidity and mortality and improved facial nerve and hearing preservation.^1–9 These findings are consistent with volume-outcome relationships that have been identified for numerous surgical procedures. With the increasing nationwide focus on patient-centered and value-based care, initiatives such as the Leapfrog Group have instituted minimum hospital surgeon standards for certain common surgical procedures. The need for high-volume, multidisciplinary dedicated teams for complex medical conditions such as ANs have led to the concept of Centers of Excellence. There is a growing body of research on this topic, in addition to the developing role of social media and patient-centered organizations such as the Acoustic Neuroma Association (ANA) in patient decision-making. Therefore, patients diagnosed with ANs may have the choice to pursue treatment at a local, low-volume hospital versus traveling larger distances to reach a high-volume center. The objective of this study was to determine the impact of travel burden and hospital volume on post-operative outcomes of patients with ANs.

Patient Population

The National Cancer Database (NCDB) is a joint program of the Commission on Cancer and the American Cancer Society. Nearly 70% of new cancer cases among patients ≥ 18 years of age in the United States from over 1500 hospital clinics are included in the database. In our analysis, we included patients diagnosed with an acoustic neuroma / vestibular schwannoma (histology codes 9560 or 9570, and site code C72.4) between 2004 and 2015. Patients were included if they underwent at least a biopsy. Patients who did not receive surgery or had an unknown surgical history were excluded.

Statistical Analysis

The primary exposures were travel distance and hospital volume. Within the NCDB, travel distance is defined as the number of miles between a patient’s residential zip code centroid and the zip code of the treating hospital. Annual surgical volume was calculated using unique facility identifiers. Two patient cohorts were defined: patients in the lowest quartile of travel distance treated at the lowest quartile of hospital volume (Short-travel/Low-Volume: STLV) and patients in the highest quartile of travel distance treated at the upper quartile of hospital volume (Long-travel/High-Volume: LTHV). Patients not meeting criteria for either group were excluded from the final analysis. Outcomes included extent of resection (coded in the NCDB starting in 2010), receipt of radiation, post-treatment 30-day readmission, overall survival, time between diagnosis and surgery, and length of stay (LOS). Long LOS was defined as the top quartile of LOS.

Binary outcomes were investigated using Pearson’s chi-square tests for univariable analysis and logistic regression for multivariable analysis. Continuous and ordinal variables were analyzed using t-tests and Wilcoxon rank-sum tests, respectively. Univariable and multivariable analyses of overall survival (OS) were completed with Cox proportional hazards models with results presented as hazard ratios (HRs). Multivariable analyses were adjusted a priori for the following patient, clinical, tumor, and hospital characteristics: age at diagnosis, race/ethnicity, Charlson-Deyo comorbidity score, insurance status, median household income of zip code, tumor laterality, tumor size, hospital type, hospital region, and hospital safety-net burden. Survival analysis was also adjusted for the receipt of radiation. Race/ethnicity included white, black, Hispanic, Asian/Pacific Islander, or other race. Patients were categorized as underinsured if they were uninsured or covered by Medicaid. Safety-net burden was defined as the proportion of Medicaid and uninsured patients treated at each hospital. Statistical analysis was completed with Stata MP Version 14.1 (Stata Corp LP). All tests were two-sided with statistical significance defined as p < 0.05.

Overall, 13,370 AN patients underwent surgery in the NCDB between 2004 and 2015. Of these, 1,305 patients were classified as STLV and traveled a median of 6 miles (Interquartile range [IQR] 3–9) to 439 low-volume centers, which performed a median of 2 (IQR 1–3) annual cases. In comparison, the LTHV cohort (n = 1,103) traveled a median of 143 miles (IQR 103–230) to 31 high-volume centers, which performed a median of 34 annual cases (IQR 28–42). Patient and hospital characteristics are summarized in Table 1. Regional variation in surgical volume and travel distance is shown in Fig. 1.

Table 1

Patient characteristics and unadjusted outcomes of STLV and LTHV patient groups
Factor	Total (n = 2,408)	STLV (n = 1,305)	LTHV (n = 1,103)	p-value
Number of Facilities	448	439	31
Annual Volume, median (IQR)	4.00 (2.00, 34.00)	2.00 (1.00, 3.00)	34.00 (28.00, 42.00)	< 0.001
Burden, median (IQR)	8.36 (4.85, 13.04)	9.55 (6.64, 13.51)	5.22 (4.06, 13.04)	< 0.001
Patient Age, mean (SD)	50.91 (13.22)	50.97 (13.84)	50.83 (12.45)	0.79
Sex				0.94
Male	1070 (44.4%)	579 (44.4%)	491 (44.5%)
Female	1338 (55.6%)	726 (55.6%)	612 (55.5%)
Median income of zip				< 0.001
<$38,000	342 (14.2%)	190 (14.6%)	152 (13.8%)
$38,000–$47,999	580 (24.1%)	259 (19.8%)	321 (29.1%)
$48,000–$62,999	724 (30.1%)	362 (27.7%)	362 (32.8%)
$63,000+	759 (31.5%)	494 (37.9%)	265 (24.0%)
Unknown	3 (0.1%)	0 (0.0%)	3 (0.3%)
Insurance				< 0.001
Not Insured	74 (3.1%)	54 (4.1%)	20 (1.8%)
Private Insurance	1747 (72.5%)	879 (67.4%)	868 (78.7%)
Medicaid	148 (6.1%)	123 (9.4%)	25 (2.3%)
Medicare	349 (14.5%)	205 (15.7%)	144 (13.1%)
Other Government	39 (1.6%)	20 (1.5%)	19 (1.7%)
Unknown	51 (2.1%)	24 (1.8%)	27 (2.4%)
Race				< 0.001
White	1922 (79.8%)	963 (73.8%)	959 (86.9%)
Black	94 (3.9%)	75 (5.7%)	19 (1.7%)
Hispanic	175 (7.3%)	150 (11.5%)	25 (2.3%)
Asian/Pacific Islander	111 (4.6%)	83 (6.4%)	28 (2.5%)
Other	106 (4.4%)	34 (2.6%)	72 (6.5%)
Distance to Hospital, median (IQR)	10.70 (5.30, 133.80)	5.70 (3.20, 8.60)	143.40 (103.10, 230.20)	< 0.001
Charlson/Deyo Score				0.007
0	2077 (86.3%)	1099 (84.2%)	978 (88.7%)
1	268 (11.1%)	162 (12.4%)	106 (9.6%)
2	50 (2.1%)	34 (2.6%)	16 (1.5%)
3	13 (0.5%)	10 (0.8%)	3 (0.3%)
Size				< 0.001
0.1–20 mm	818 (34.0%)	357 (27.4%)	461 (41.8%)
21–40 mm	850 (35.3%)	525 (40.2%)	325 (29.5%)
41–60 mm	177 (7.4%)	121 (9.3%)	56 (5.1%)
61–80 mm	12 (0.5%)	7 (0.5%)	5 (0.5%)
81–100 mm	6 (0.2%)	4 (0.3%)	2 (0.2%)
>100 mm	26 (1.1%)	10 (0.8%)	16 (1.5%)
Unknown	519 (21.6%)	281 (21.5%)	238 (21.6%)
Laterality				0.001
Right	1168 (48.5%)	616 (47.2%)	552 (50.0%)
Left	1174 (48.8%)	638 (48.9%)	536 (48.6%)
Bilateral/Midline	63 (2.6%)	48 (3.7%)	15 (1.4%)
Unknown	3 (0.1%)	3 (0.2%)	0 (0.0%)
Facility Type				< 0.001
Community Cancer Program	41 (1.7%)	41 (3.1%)	0 (0.0%)
Comprehensive Community Cancer Program	553 (23.0%)	417 (32.0%)	136 (12.3%)
Academic/Research Program	1126 (46.8%)	401 (30.7%)	725 (65.7%)
Integrated Network Cancer Program	186 (7.7%)	160 (12.3%)	26 (2.4%)
Other/Unknown	502 (20.8%)	286 (21.9%)	216 (19.6%)
Year of diagnosis				0.004
2004	166 (6.9%)	101 (7.7%)	65 (5.9%)
2005	201 (8.3%)	110 (8.4%)	91 (8.3%)
2006	227 (9.4%)	114 (8.7%)	113 (10.2%)
2007	217 (9.0%)	114 (8.7%)	103 (9.3%)
2008	163 (6.8%)	91 (7.0%)	72 (6.5%)
2009	222 (9.2%)	95 (7.3%)	127 (11.5%)
2010	199 (8.3%)	111 (8.5%)	88 (8.0%)
2011	177 (7.4%)	94 (7.2%)	83 (7.5%)
2012	196 (8.1%)	108 (8.3%)	88 (8.0%)
2013	208 (8.6%)	134 (10.3%)	74 (6.7%)
2014	227 (9.4%)	116 (8.9%)	111 (10.1%)
2015	205 (8.5%)	117 (9.0%)	88 (8.0%)
Extent of Resection				< 0.001
Biopsy	154 (21.2%)	115 (27.4%)	39 (12.7%)
Subtotal Resection	229 (31.5%)	166 (39.5%)	63 (20.5%)
Gross Total Resection	345 (47.4%)	139 (33.1%)	206 (66.9%)
Radiation	128 (5.3%)	120 (9.3%)	8 (0.7%)	< 0.001
30-day mortality	23 (1.1%)	18 (1.6%)	5 (0.5%)	0.016
90-day mortality	35 (1.7%)	28 (2.5%)	7 (0.7%)	0.001
30-day readmission	157 (6.5%)	100 (7.7%)	57 (5.2%)	0.013
30-day unplanned readmission	128 (5.3%)	76 (5.8%)	52 (4.7%)	0.23
Diagnosis to surgery (days), mean (SD)	57.45 (112.98)	48.14 (63.80)	68.63 (151.63)	< 0.001
LOS from surgery (days), mean (SD)	5.58 (6.54)	6.25 (8.32)	4.88 (3.74)	< 0.001

Compared to STLV patients, LTHV patients had lower Charlson/Deyo scores (p = 0.001), mostly received care at academic centers (65.7% vs 30.7%, p < 0.001), were less likely to be minorities (7.0% vs 24.2%, p < 0.001) or underinsured (4.2% vs 13.8%, p < 0.001), and were more likely to have private insurance (78.7% vs 67.4%, p < 0.001). LTHV patients were treated at hospitals with lower safety net burden (5.2 vs 9.6, p < 0.001). There was no difference in age, sex, or average tumor size.

Geographic variations included more LTHV patients treated in centers located in the South Atlantic (19.6% vs. 13.3%), East North Central (15.9% vs. 11.9%), and West North Central (25.4% vs. 6.2%) regions relative to STLV patients. In contrast, more STLV patients were treated in New England (3.9% vs. 0%), Middle Atlantic 11.8% vs. 1.2%), Mountain (6.9% vs. 0.6%), and Pacific (11.6% vs. 7.0%) regions relative to LTHV patients.

Multivariable regression analyses were completed with both hospital volume and residential distance from the hospital treated as continuous variables, and then as categorical variables in quartiles. Hospital volume was significantly associated with increased likelihood of GTR and longer duration between diagnosis and surgery, reduced odds of 30-day readmission and prolonged length of stay, and lower HR of death (Table 2). No consistent relationship was identified between distance and any of the outcomes studied.

Table 2

Results of multivariable analyses evaluating the impact of hospital volume and travel distance on outcomes. Covariates are excluded from the table. Abbreviations: GTR, gross total resection; LOS, length of stay; OS, overall survival; OR, odds ratio; HR, hazard ratio.
		Continuous			Categorical
		OR/HR	95% CI	p	OR/HR	95% CI	p
Hospital Volume	GTR	1.037	1.032,1.043	< 0.001	3.389	2.775,4.139	< 0.001
	30d readmit	0.989	0.983,0.995	< 0.001	0.716	0.572,0.895	0.003
	Time to Surgery	1.005	1.001,1.008	0.004	1.15	1.008,1.311	0.037
	Long LOS	0.989	0.985,0.993	< 0.001	0.586	0.506,0.679	< 0.001
	OS	0.988	0.981,0.995	0.001	0.608	0.470,0.786	< 0.001
Distance	GTR	1.001	1.000,1.001	0.021	1.162	0.959,1.409	0.126
	30d readmit	1	0.999,1.000	0.319	0.936	0.754,1.162	0.552
	Time to Surgery	1	1.000,1.000	0.85	1.069	0.941,1.215	0.305
	Long LOS	1	1.000,1.000	0.314	0.892	0.770,1.034	0.13
	OS	0.999	0.999,1.000	0.125	0.812	0.629,1.048	0.109

Subsequent analyses included only those patients in the STLV or LTHV groups (Table 3). On multivariable analysis, LTHV patients had an increased likelihood of gross total resection (odds ratio [OR] 5.6, 95% confidence interval [CI] 3.8–8.4, p < 0.001), longer duration between diagnosis and surgery (OR 1.3, 95% CI 1.0-1.6, p = 0.040), decreased length of hospital stay (OR 0.5, 95% CI 0.4–0.7, p < 0.001), and greater overall survival (HR 0.6, 95% CI 0.4–0.95, p = 0.029), Fig. 2. STLV patients were much more likely to undergo radiation (OR 12.3, 95% CI 5.8–26.1, p < 0.001). There was no significant difference in 30-day readmission on adjusted analysis.

Table 3

Results of multivariable analyses. *Because extent of resection was not included within the NCDB until 2010, the years 2004–2009 are excluded from the analysis of gross total resection. Abbreviations: OR, odds ratio; β, standardized beta coefficient; HR, hazard ratio.
	Gross Total Resection			30d Readmission			Time to Surgery			Long LOS			Overall Survival
	OR	95% CI	p	OR	95% CI	p	β	95% CI	p	OR	95% CI	p	HR	95% CI	p
Travel/Volume
STLV (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
LTHV	5.639	3.769,8.438	< 0.001	0.733	0.491,1.094	0.128	1.284	1.011,1.632	0.04	0.5	0.384,0.652	< 0.001	0.576	0.360,0.920	0.021
Age
18–49 (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
50–69	0.618	0.405,0.942	0.025	0.717	0.475,1.080	0.112	0.993	0.761,1.296	0.961	1.289	0.952,1.745	0.101	2.624	1.354,5.084	0.004
70+	0.407	0.181,0.919	0.03	1.45	0.686,3.062	0.33	0.864	0.500,1.492	0.599	1.954	1.154,3.309	0.013	6.653	3.048,14.521	< 0.001
Sex
Male (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
Female	0.9	0.644,1.258	0.537	0.937	0.672,1.308	0.704	1.09	0.885,1.343	0.416	1.122	0.894,1.408	0.32	0.718	0.501,1.030	0.072
Median income of zip
<$38,000 (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
$38,000- $47,999	1.63	0.933,2.847	0.086	1.183	0.669,2.094	0.563	0.604	0.429,0.851	0.004	0.947	0.655,1.367	0.77	1.269	0.740,2.176	0.386
$48,000–62,999	1.494	0.872,2.560	0.144	1.141	0.650,2.001	0.646	0.719	0.518,0.997	0.048	0.812	0.565,1.166	0.259	0.728	0.411,1.292	0.278
$63,000+	1.769	1.026,3.051	0.04	1.125	0.641,1.974	0.682	0.891	0.641,1.237	0.491	1.015	0.712,1.447	0.933	0.691	0.383,1.248	0.22
Insurance
Not Insured (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
Private Insurance	0.305	0.119,0.782	0.013	0.794	0.338,1.867	0.597	1.503	0.749,3.014	0.251	0.452	0.258,0.792	0.006	1.37	0.411,4.562	0.608
Medicaid	0.369	0.121,1.128	0.08	1.244	0.474,3.271	0.657	2.157	0.980,4.747	0.056	1.002	0.525,1.911	0.995	2.816	0.786,10.090	0.112
Medicare	0.299	0.101,0.887	0.03	0.629	0.230,1.722	0.367	1.507	0.707,3.212	0.288	0.455	0.237,0.875	0.018	3.822	1.107,13.189	0.034
Other Government	0.0501	0.007,0.344	0.002	1	--	--	1.658	0.582,4.726	0.344	0.511	0.171,1.521	0.228	4.687	0.891,24.638	0.068
Unknown	0.264	0.071,0.983	0.047	1	--	--	1.067	0.380,2.998	0.902	0.817	0.324,2.061	0.669	1.721	0.275,10.763	0.562
Race
White (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
Black	1.868	0.822,4.244	0.136	0.557	0.196,1.584	0.272	1.006	0.586,1.726	0.983	1.876	1.123,3.136	0.016	3.402	1.750,6.613	< 0.001
Hispanic	1.57	0.850,2.899	0.149	1.474	0.836,2.599	0.18	1.332	0.876,2.026	0.18	1.3	0.858,1.970	0.216	1.87	0.968,3.612	0.062
Asian/Pacific Islander	2.229	1.072,4.632	0.032	0.956	0.445,2.053	0.907	0.643	0.359,1.150	0.136	1.906	1.214,2.992	0.005	2.203	1.127,4.307	0.021
Other	0.605	0.212,1.730	0.349	0.739	0.262,2.081	0.566	1.04	0.613,1.764	0.885	0.876	0.465,1.651	0.682	0.75	0.230,2.445	0.633
Charlson/Deyo Score
0 (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
1	0.72	0.421,1.232	0.231	1.087	0.655,1.804	0.747	1.311	0.948,1.812	0.101	1.307	0.936,1.827	0.116	1.74	1.140,2.656	0.01
2	2.445	0.806,7.418	0.114	1.143	0.391,3.338	0.807	1.203	0.599,2.415	0.604	1.897	0.975,3.690	0.059	1.658	0.759,3.623	0.204
3	7.079	0.661,75.766	0.106	3.411	0.839,13.870	0.086	0.237	0.029,1.912	0.176	0.71	0.180,2.800	0.625	5.011	1.681,14.937	0.004
Tumor Size
0–2 cm (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
2–4 cm	0.645	0.430,0.966	0.033	1.253	0.839,1.871	0.27	0.453	0.355,0.577	< 0.001	2.337	1.736,3.148	< 0.001	3.023	1.758,5.198	< 0.001
> 4 cm	0.281	0.145,0.545	< 0.001	1.092	0.590,2.019	0.78	0.251	0.158,0.399	< 0.001	3.644	2.430,5.463	< 0.001	2.974	1.422,6.221	0.004
Unknown	0.839	0.509,1.385	0.493	0.754	0.450,1.264	0.284	0.311	0.229,0.422	< 0.001	1.765	1.256,2.479	0.001	2.032	1.130,3.656	0.018
Tumor Laterality
Right (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
Left	1.218	0.874,1.698	0.244	1.043	0.747,1.455	0.806	0.775	0.629,0.956	0.017	0.986	0.786,1.237	0.903	1.112	0.775,1.595	0.563
Bilateral/Midline	8.626	1.381,53.866	0.021	0.422	0.099,1.800	0.244	0.848	0.406,1.771	0.66	0.542	0.245,1.198	0.13	0.842	0.287,2.469	0.753
Facility Type
Community Cancer Program (Ref)	1	--	--	1	--	--	1	--	--	1	--	--	1	--	--
Comprehensive Community Cancer Program	1.298	0.289,5.825	0.734	1.346	0.387,4.677	0.641	0.388	0.166,0.905	0.029	1.423	0.514,3.943	0.497	0.456	0.206,1.009	0.053
Academic/Research Program	1.341	0.304,5.904	0.698	1.33	0.383,4.614	0.654	0.821	0.357,1.887	0.641	1.476	0.534,4.076	0.453	0.384	0.170,0.868	0.021
Integrated Network Cancer Program	2.229	0.466,10.659	0.315	1.538	0.414,5.718	0.52	0.642	0.265,1.556	0.327	1.536	0.532,4.439	0.428	0.467	0.191,1.143	0.095
Other/unknown	0.961	0.211,4.389	0.959	0.778	0.212,2.860	0.706	0.513	0.216,1.219	0.13	1.771	0.619,5.070	0.287	0.289	0.086,0.976	0.046
Year*
2004	--	--	--	1	--	--	1	--	--	1	--	--	1	--	--
2005	--	--	--	1.199	0.555,2.587	0.644	1.073	0.573,2.007	0.827	0.723	0.425,1.230	0.232	1.558	0.773,3.142	0.215
2006	--	--	--	0.888	0.400,1.970	0.77	1.749	0.993,3.081	0.053	0.564	0.330,0.964	0.036	1.17	0.540,2.538	0.69
2007	--	--	--	0.597	0.252,1.412	0.24	1.117	0.613,2.035	0.717	0.558	0.324,0.962	0.036	1.184	0.512,2.736	0.693
2008	--	--	--	0.788	0.329,1.888	0.593	1.972	1.075,3.618	0.028	0.508	0.283,0.912	0.023	0.95	0.405,2.228	0.906
2009	--	--	--	0.873	0.393,1.940	0.739	0.871	0.476,1.594	0.654	0.562	0.327,0.965	0.037	1.016	0.427,2.417	0.971
2010	1	--	--	0.834	0.370,1.877	0.661	2.314	1.310,4.088	0.004	0.529	0.303,0.923	0.025	0.757	0.298,1.924	0.558
2011	1.242	0.692,2.229	0.467	0.544	0.216,1.369	0.196	1.732	0.954,3.144	0.071	0.628	0.359,1.096	0.101	1.257	0.486,3.255	0.637
2012	1.185	0.668,2.103	0.561	1.312	0.621,2.773	0.477	1.642	0.917,2.938	0.095	0.341	0.190,0.613	0	0.418	0.129,1.357	0.147
2013	1.003	0.562,1.790	0.992	0.566	0.239,1.344	0.197	2.879	1.641,5.053	0	0.577	0.338,0.985	0.044	2.34	1.015,5.394	0.046
2014	1.172	0.668,2.056	0.581	1.109	0.521,2.358	0.788	2.354	1.351,4.101	0.003	0.613	0.364,1.033	0.066	1.097	0.387,3.108	0.862
2015	1.158	0.663,2.023	0.607	0.491	0.201,1.198	0.118	2.03	1.156,3.564	0.014	0.576	0.334,0.993	0.047	--	--	--
Radiation	--	--	--	--	--	--	--	--	--	--	--	--	0.624	0.262,1.487	0.287
Observations	727			2312			2261			2215			2189

In this study, we examined the impact of travel distance and hospital volume on treatment characteristics and post-surgical outcomes for a nationwide cohort of newly diagnosed ANs. As many patients with ANs do not live near a high-volume center, we sought to determine if overcoming the travel burden to a high-volume center instead of receiving care locally at a low-volume center resulted in a meaningful clinical benefit. Given that ANs are typically slow-growing and treated in an elective fashion, patients may have time to arrange for longer travel to a high-volume center without the risk of disease progression or clinical deterioration. Our study demonstrates that despite an expected delay in treatment associated with long travel distance (as well as likely delays in establishing care with a second provider), patients treated at high-volume hospitals are more likely to receive maximal tumor resection and have improved short- and long-term post-operative outcomes (including overall survival) as compared to those treated locally at low-volume centers. This is the first study to characterize the distance-volume relationship on outcomes for ANs.

Volume-outcome relationship in AN

Prior studies have characterized the volume-outcome relationship in ANs. High surgeon volume has been associated with reduced risk for postoperative complications, shorter length of stay, and lower hospital charges.¹ Similarly, high volume centers have been shown to have lower complication rates, length of stay, costs, need for postoperative intervention for hydrocephalus, and nonroutine discharge.^{1,2, 4–6,8,9} For AN surgery, which is highly specialized and is frequently performed by a single neurosurgeon-otolaryngologist team (rather than a variety of surgeons) at a given institution, surgeon volume and hospital volume are often synonymous.

In the current work, we found that annual hospital operative volume was independently associated with an increased likelihood of GTR and longer OS, as well as a reduced likelihood of long hospital stay or 30-day readmission. Operative mortality has been previously studied in the NCDB.¹⁰ However, a survival benefit associated with high-volume hospitals has not been previously reported and is among the important findings of this study. Due to the predominantly benign pathology of ANs, this likely reflects a difference in the quality of surgical management rather than the natural history of the disease.

GTR is the goal of AN surgery when it can be done safely, as GTR is associated with reduced tumor recurrence that could necessitate reoperation or radiation.¹¹ However, the goal of GTR for benign schwannomas is superseded by preservation of facial nerve function, and in some cases, hearing preservation or protection of the brainstem. Higher rates of GTR, lower complication rates, and increased likelihood of routine discharge have previously been associated with greater surgeon/hospital volume and experience.^1,5,8,9,12 However, some studies have identified greater morbidity associated with GTR due to adherence between the facial nerve and tumor, particularly just medial to the porous acousticus.¹³ Our finding that both surgical morbidity and mortality are lower for high-volume hospitals suggests that highly experienced AN surgeons can achieve GTR while also minimizing the risk of complications.

Long Travel High Volume versus Short Travel Low Volume

We found that LTHV patients had an increased likelihood of GTR, shorter hospital length of stay, and greater overall survival, suggesting that overcoming the travel burden in order to receive care at a high-volume center is worth the wait for those with the socioeconomic means to do so.

The impact of residential distance on CNS tumor outcome was studied by Johnson et al. using the NCDB.¹⁴ The study population was adolescents and young adults with primary brain and intraspinal tumors. For patients with low-grade astrocytic tumors and ependymomas, increased distance to the hospital was associated with a reduced risk of death and mediated by facility volume. These findings mirror our results for AN, which suggests that this effect may specifically pertain to tumor types that are relatively slow growing and have very high survival.

Interestingly, a study on GBM by Lopez Ramos et al. used methods similar to the current work and also identified a significant survival advantage for GBM patients traveling long distances for high volume care.¹⁵ While rates of GTR were the same between STLV and LTHV hospitals, the utilization of standard-of-care adjuvant chemotherapy was significantly higher at LTHV hospitals, suggesting that aspects of care other than surgical technique may play a critical role in defining outcomes in patients with more aggressive CNS tumors.

In the current work, LTHV patients had fewer medical comorbidities than STLV patients and had lower proportion of Black, Hispanic, or Asian/Pacific Islander patients. They were also more likely to have private insurance and less likely to be underinsured. Unlike STLV hospitals, LTHV hospitals were mostly academic centers. An effect of race on AN management has been previously analyzed, with one prior study of the SEER database reporting that Black patients with ANs were more likely to receive recommendations against surgical resection compared with White patients.¹⁷ Regarding surgical outcomes, studies have identified a higher rate of mortality of African American patients undergoing resection by low-caseload surgeons.¹⁶ This has led prior authors to suggest that perhaps under-resourced patient populations should be preferentially managed with minimally invasive options such as observation, fractionated stereotactic radiotherapy, or stereotactic radiosurgery.¹⁶ However, treatment disparities in ANs may also extend to radiation therapy, as an NCDB study found that patients treated with Gamma Knife had greater proportions of private insurance, higher incomes, treatment in academic centers and high-volume facilities compared to those treated with a Linear Accelerator.¹⁸ Although the ideal solution to these findings is an equitably distribution of care for all AN patients, it remains unclear how to either increase access to high-volume centers or optimize outcomes in lower volume centers for patients with limited resources.

To date, there are limited data regarding the impact of travel burden to high volume centers on outcomes for skull base tumors such as ANs. Patients’ decisions to travel substantial distances to high-volume centers are complex and multifactorial. While financial resources and healthcare literacy likely play a significant role, the blossoming of online patient education, social media, and social networking such as the Acoustic Neuroma Association in which patients can directly exchange information regarding the facets of their care undoubtedly have impacted the way patients choose their surgeons. Recognizing the value of traveling to high-volume AN hospitals is increasingly important, as certain employers and insurance carriers may consider providing financial incentives to seeking care at Centers of Excellence.¹⁹

Limitations

In this study, we calculated hospital volume based on unique hospital identifiers provided by the NCDB. Unfortunately, unique surgeon identifiers were not available, so we were unable to determine surgeon volume. Limitations of this study include the fact that surgeon experience may not equate to surgeon volume (i.e., a high-volume practice in a given year may not necessarily reflect many years of high volume). The same is true for hospitals, which may have a referral pattern that persists even when experienced surgeons retire or leave. High-volume surgeons can move to new institutions and create new high-volume centers; in these situations, the centers have a relatively little experience whereas the surgeon may have decades of it.

Furthermore, retrospective analysis of the NCDB has its own limitations. Data are derived only from Commission on Cancer (CoC)-accredited cancer programs. Additionally, important anatomic characteristics (such as the position of the facial and vestibular nerves relative to the tumor), surgical details (including the approach used), and outcomes that may be important to quality of life (such as postoperative facial nerve and hearing status), were not available. Finally, because NCDB data include only the “first course of treatment” (all methods of treatment administered before disease progression or recurrence), the need for additional surgeries or radiation for residual or recurrent tumor cannot be assessed.

Although traveling farther to high-volume centers increased the time between diagnosis and treatment for AN patients, they experienced superior postoperative outcomes compared to patients who received treatment locally at low-volume centers. Enabling access and travel to high-volume centers may improve AN patient outcomes.

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No competing interests reported.

Going the Distance in Acoustic Neuroma Resection: Microsurgical Outcomes at High-Volume Centers of Excellence

Status:

Journal Publication

Version 1

Abstract

Figures

Introduction

Methods

Patient Population

Statistical Analysis

Results

Discussion

Volume-outcome relationship in AN

Long Travel High Volume versus Short Travel Low Volume

Limitations

Conclusions

References

Additional Declarations

Status:

Journal Publication

Version 1