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Identification of the Wedge-Sickle Sign Associated with Fibromuscular Bands in Neurogenic Thoracic Outlet Syndrome Using MR Neurography: A Case Report
Sophie Queler
*1, Delaram Shakoor
1, Ajul Shah
2, Ek Tsoon Tan
1, Darryl Sneag
11Hospital for Special Surgery, Brooklyn, NY; 2Plastic Surgery, The Institute for Advanced Reconstruction, New York, NY
Background: The lower nerve roots (C8-T1) and lower trunk of the brachial plexus may be impinged by congenital, fibromuscular bands causing neurogenic thoracic outlet syndrome (nTOS). The sonographic "˜wedge-sickle' sign has been previously used to describe indentation of neural structures by such bands but has not been reported on magnetic resonance neurography (MRN). Here, we describe on MRN the wedge-sickle sign and subsequent creation of three-dimensional digital and printed models to guide surgical decompression.
Methods: Brachial plexus MRI at 3.0 Tesla was performed at our institution in a 17-year-old female who had progressive right arm numbness, cramping, burning pain and muscle atrophy (Fig. 1a-b). The imaging protocol comprised multiplanar proton density fast-spin-echo (FSE), T2-weighted fat-suppressed 2-point Dixon, oblique coronal 3D FSE short tau inversion recovery (STIR) and double echo steady state (DESS) sequences. A 3D zero time to echo (ZTE) sequence was also acquired to enhance visualization of osseous structures. Additionally, contrast-enhanced MR angiography was performed to better delineate the relevant vasculature. 3D renderings were created.
Results: Nerve conduction studies revealed slowing in the median and ulnar nerves. MRN revealed prominent enlargement of the right C8 nerve root and lower trunk and compression of the lower trunk between a suspected fibrous band arising from a small cervical rib (Fig. 1c-d), redemonstrated on 3D rendering (Fig. 1e-f). Decompression surgery confirmed the presence of the fibrous band causing kinking and severe impingement of the lower trunk (Fig. 1g-i).
Conclusion: MRN can demonstrate the analogous finding of the sonographic wedge-sickle sign. This finding may enhance the sensitivity of MRN's detection of fibromuscular bands, which may be thin and challenging to visualize particularly given their oblique course.
