MR neurography (MRN) of the long thoracic nerve: retrospective review of clinical findings and imaging results at our institution over 4 years

Objective: Long thoracic nerve (LTN) injury can result in ipsilateral serratus anterior palsy and scapular winging. Traditional means of evaluating patients with suspected LTN injury include physical examination and electrodiagnostic studies. The purpose of our study is to describe high-resolution magnetic resonance (MR) findings in patients with clinical suspicion of LTN neuropathy. Methods: In this HIPAA-compliant, IRB-approved, retrospective study, two radiologists reviewed MR imaging performed for long thoracic neuropathy. Clinical presentation, electrodiagnostic studies and MR imaging of 20 subjects [mean age 37 ± 13 years; 25% (5/20) female] were reviewed. Observers reviewed MR imaging for LTN signal intensity, size, course, presence or absence of mass and secondary findings [skeletal muscle denervation (serratus anterior, trapezius, rhomboid) and scapular winging]. Descriptive statistics were reported. Results: Clinical indications included trauma (n = 5), hereditary neuropathy (n = 1), pain (n = 8), winged scapula (n = 6), brachial plexitis (n = 4) and mass (n = 1). Electrodiagnostic testing (n = 7) was positive for serratus anterior denervation in three subjects. Abnormal LTN signal intensity, size, course or mass was present in 0/20. Secondary findings included skeletal muscle denervation in the serratus anterior in 40% (8/20), trapezius in 20% (4/20) and rhomboid in 20% (4/20). In 5% (1/20), an osteochondroma simulated a winged scapula, and in 2/20 (10%) MR showed scapular winging. Conclusions: High-resolution MR imaging is limited in its ability to visualize the long thoracic nerve directly, but does reveal secondary signs that can confirm a clinical suspicion of LTN injury.