The diagnostic accuracy of CT-based "Banner cloud sign" for dural ossification in patients with thoracic ossification of the ligamentum flavum: a prospective, blinded, diagnostic accuracy study protocol

Background: Ossification of the ligamentum flavum (OLF) is the most common cause of thoracic spinal stenosis, which responds poorly to conservative treatment. Thus, surgery is the only effective treatment for OLF. The existence of dural ossification (DO) makes surgery challenging and increases the risk of intra-/post-operative complications. To date, several methods have been proposed to identify DO, but either the diagnostic accuracy is low or the feasibility is poor. Therefore, the aim of this study was to propose a new imaging sign (Banner cloud sign, BCs), evaluate the accuracy of BCs in the diagnosis of DO, and provide reliable evidence-based data for its application in clinical practice. Methods: A prospective, blinded, diagnostic accuracy study will be conducted to assess and compare the accuracy of BCs in the diagnosis of DO with other radiological signs [Tram track sign (TTs) and Comma sign (Cs)]. A total of 120 patients diagnosed with OLF who underwent decompression at the Peking University Third Hospital between January 2018 and June 2019 will be enrolled. Patients' medical records and imaging data will be retrieved from the hospital database server. An observational group consisting of six spine surgeons (with different seniority levels) and two epidemiological researchers will read the patients' images to identify typical imaging signs and determine the presence of DO. Surgical records will be reviewed to confirm the presence of DO, and the results will serve as the reference standard for estimating accuracy. The primary outcome of the study is to determine the accuracy of BCs for DO diagnosis, and the secondary outcome is to compare the sensitivity, specificity, area under the receiver operating characteristic (ROC) curve and inter-observer reliability of each imaging sign. The time taken and level of confidence in DO diagnosis of each observer will also be compared. Discussion: This study represents the first large-scale investigation of the diagnostic value of BCs, TTs and Cs in the diagnosis of DO, and will provide convincing evidence about their clinical application.