Chunky yarn sign: A screening marker for brachial plexus hypertrophy on axial cervical spine MRI

Background Nerve hypertrophy is one of the characteristic features of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). The brachial plexus runs along the gap between the anterior and medial scalene muscles (interscalene gap), and its enlargement sometimes appears as widening of the interscalene gap on conventional axial cervical spine MRI.Methods To determine whether the screening of nerve hypertrophy in CIDP is available via conventional cervical spine MRI, we reviewed the medical records of 29 patients with CIDP who underwent cervical MRI, and imaging features were compared with 50 patients with cervical spondylosis who underwent nerve conduction study and were confirmed to have no neuropathies. The maximum diameter of the interscalene gap at the 6th or 7th cervical vertebra level on axial-slice T2 weighted imaging was measured by two observers independently.Results The maximum diameter of the interscalene gap was significantly larger in the CIDP patients (range, 1.7-11.58; median, 3.64 mm; interquartile range [IQR], 1.79) than in the cervical spondylosis patients (range, 0.87-4.71; median, 1.96 mm; IQR, 0.88) (p < 0.001).Conclusion The enlarged interscalene gaps were analogous to chunky yarn, with a continuous thick structure along the gaps. Attention to interscalene gaps on routine MRI can contribute to the screening of hypertrophic neuropathies without additional costs or procedures.

Automated summary

This study found that the maximum diameter of the interscalene gap was significantly larger in CIDP patients compared to patients with cervical spondylosis. It suggests that conventional cervical spine MRI can be used as a screening tool for nerve hypertrophy in CIDP.