Quantitative Computed Tomography and Magnetic Resonance Assessment of Vascular Compression in the Thoracic Outlet

Objective: Diagnostic criteria for venous and arterial thoracic outlet syndrome (TOS) are heterogeneous. Detailed guidance on imaging methods and reporting is lacking. This study examined the reliability of a standardised method to quantify vascular compression in the thoracic outlet on dynamic computed tomography (CT) and magnetic resonance (MR) imaging. Methods: A standardised and pragmatic method to calculate changes in area using the major and minor diameter of the subclavian artery and vein in the sagittal plane during adduction and abduction was investigated. In a single TOS expertise centre, all CT and MR scans performed according to the TOS protocol were retrospectively identified and independently analysed by four observers using the pre-defined measurement method. Intraclass correlation coefficients were calculated to assess inter- and intra-observer reliability, with thresholds of < 0.5 (poor), 0.5 – 0.75 (moderate), > 0.75 – 0.9 (good), and > 0.9 (excellent). Results: Fifty-one CT scans (102 arms) and 58 MR scans (116 arms) were analysed. Venous compression (> 50%) was more prevalent compared with arterial compression both in the CT (51% vs. 16%) and MR (64% vs. 2%) cohorts. Interobserver agreement for CT measurements was 0.79 (95% confidence interval [CI] 0.69 – 0.86) and 0.82 (95% CI 0.75 – 0.88) for arterial and venous compression, respectively; intra-observer agreement was 0.80 (95% CI 0.72 – 0.86) and 0.84 (95% CI 0.76 – 0.89), respectively. For MR measurements, interobserver agreement was 0.36 (95% CI 0.16 – 0.53) and 0.38 (95% CI 0.20 – 0.54) for arterial and venous compression, respectively; intra-observer agreement was 0.39 (95% CI 0.23 – 0.54) and 0.60 (95% CI 0.47 – 0.71), respectively. Conclusion: The pre-defined measurement protocol applied to standard CT imaging proved reliable for both arterial and venous quantification of vascular compression. The same measurement protocol applied on MR imaging showed poor inter- and intra-observer reliability. Use of this standardised measurement protocol with CT in prospective multicentre studies on vascular TOS is advocated.