Identification of long thoracic nerve on high-resolution 3T MRI

Long thoracic neuropathy results in serratus anterior muscle denervation and presents with scapular winging. Previously published studies have been unable to identify the long thoracic nerve on MRI; instead, secondary imaging features of serratus anterior muscle denervation are used to infer nerve injury. Our study's purpose was to evaluate the ability of high-resolution MRI to depict the long thoracic nerve.

In this HIPAA-compliant, IRB-approved retrospective study, two musculoskeletal radiologists reviewed the brachial plexus MRI exans of 24 subjects performed for clinical suspicion of long thoracic neuropathy. The radiologists evaluated whether the long thoracic nerve could be identified and for the presence of serratus anterior denervation; when the nerve was seen, assessment for nerve enlargement, signal hyperintensity, and morphologic change was performed. Inter-observer reliability was estimated with Cohen's kappa (κ). Clinical presentation and electromyogram (EMG) were then reviewed.

The long thoracic nerve was identified in 18 cases (75%), with high inter-observer reliability for nerve visualization. Kappa values of 1.0, 0.9, 1.0, and 0.9 were obtained for identification of the LTN on coronal sequences of the brachial plexus, identification of the LTN on proximal and mid segments of the nerve on oblique sagittal sequences, and identification of the distal segment of the LTN on axial sequences through the chest, respectively. The nerve was identified in 91% of patients with positive EMG findings for a long thoracic neuropathy. In patients with EMG features of long thoracic neuropathy, 70% had corresponding abnormal MRI features. When denervation edema was present, the nerve was identified 86% of the time.

High-resolution MRI can be used to visualize segments of the long thoracic nerve.