Thoracic Outlet Syndrome: Diagnostic Accuracy of MRI

Background: Thoracic outlet syndrome (TOS) is challenging to diagnose, as the physical findings and investigations lack sensitivity and/or specificity. Magnetic resonance imaging (MRI) with dynamic manoeuvres can rule out a tumour and detect anatomical abnormalities potentially responsible for compression. The objective of this study was to assess the sensitivity and specificity of MRI for identifying anatomical structures responsible for compression in TOS, using intra-operative findings as the diagnostic reference standard.

Hypothesis: MRI is effective in diagnosing the source of compression in TOS, notably within the scalene triangle and at the pleural apex.

Methods: We retrospectively included 48 patients who underwent surgery for TOS after a work-up that included MRI (1.5-T, n=29 and 3-T, n=19). The MRI scans were reviewed for the study by a specialised radiologist who was unaware of the intra-operative findings. The sensitivity and specificity of MRI for diagnosing TOS were estimated using the intra-operative findings as the reference standard.

Results: MRI identified a structure potentially responsible for TOS in 34 (71%) patients; thus, the false-negative rate was 14/48 (29%). The sensitivity of MRI was 28% for compression at the suspensory ligament of the pleural dome, 81% for hypertrophy of the anterior scalene muscle, and 50% for an accessory scalene muscle. For diagnosing a cervical rib, MRI had 100% sensitivity and 100% specificity.

Conclusion: MRI can contribute to the diagnosis of TOS. Specificity is sufficiently high to provide guidance for planning the surgical procedure. Sensitivity, however, is too low for MRI to be useful as a screening test. MRI should be used in combination with the clinical assessment and other investigations to assist in the diagnosis of TOS.

Level of evidence: IV, retrospective cohort study.