Validation of the Skull Base Inventory Quality of Life Questionnaire in a Multi-institutional Prospective Cohort Study of Patients Undergoing Open and Endoscopic Skull Base Surgery

Background: Surgical treatment for skull base neoplasms has seen much advancement over the past two decades. Oncological outcomes have steadily improved and are well understood. However, sound knowledge of the quality of life (QOL) in patients treated for these neoplasms is lacking. The Skull Base Inventory (SBI) was developed as a means to better assess QOL in patients with anterior and central skull base neoplasms treated by both endoscopic and open approaches. Previous studies have shown satisfactory psychometric properties of the SBI in cross-sectional analysis, but none have yet reported gold-standard prospective reliability and validity measures.

Methods: The current study is part of a multicenter, prospective cohort study examining endoscopic and open procedures from 2012 to 2018. The SBI is a 11-domain questionnaire with 41 items, previously generated through chart review, systematic review, expert opinion, and patient focus groups, with item reduction through an impact score method. The SBI was administered at several time points, including preoperatively, 2-weeks postoperatively, and 3, 6, and 12-months postoperatively. Reliability of the SBI was assessed through test–retest and internal consistency. Concurrent validity was assessed through comparison with the Anterior Skull Base (ASB) questionnaire and the Sinonasal Outcome Test (SNOT-22). Convergent validity was assessed through comparison of five global QOL ratings (ranging from “much worse” to “much better”). Discriminative validity was assessed by comparing SBI score between the preoperative time period and the acute postsurgical period (2-weeks). The minimally important clinical difference was determined as the mean change in SBI score in patients who rated their symptoms as “a little better” or “a little worse.”

Results: One-hundred eighty-seven patients were included across five centers, with 121 having an endoscopic procedure. The mean age was 53.5 years, and the majority of patients were female (60%). Internal consistency was excellent (Cronbach’s α ¼ 0.95). Test–retest at 12-months and 12- months plus 2 weeks was also excellent (intraclass correlation > 0.90) in all SBI domains except two. Concurrent
validity was demonstrated by the presence of a very strong correlation, at all-time points, between total SBI scores and ASB scores (range of r ¼ 0.810–0.869, p < 0.001), and moderate correlation of the nasal domain SBI scores with SNOT-22scores (range of r ¼ 0.616 to 0.738, p < 0.001). Convergent validity was demonstrated by the presence of a moderate correlation of the mean change in SBI scores with the
global QOL ratings from preoperative to 1-year postoperative (rs ¼ 0.4942, p < 0.001). The SBI demonstrates discriminative validity, showing significant mean differences between the preoperative and 2-week periods, for total scores and seven of the domains (emotional, family, financial, social, nasal, neurologic, and other). Lastly, the minimally important clinical difference was determined to be 6.0 out of a possible
100.

Conclusion: The SBI questionnaire is reliable and valid for patients treated with endoscopic and open approaches for anterior skull base neoplasms, and can be used for assessment of QOL in this setting.