MR imaging of entrapment neuropathies of the shoulder

LEARNING OBJECTIVES: To describe the MRI features of most common entrapment neuropathies of the shoulder: - Parsonage-Turner syndrome - quadrilateral space syndrome (axillary neuropathy) - suprascapular nerve syndrome BACKGROUND: Entrapment neuropathies are characterized by alteration of nerve function secondary to compression by mechanical or dynamic forces. The compression may be acute, chronic or intermittent. Not infrequently compressive neuropathies are related to space-occupying lesions such as tumors, cysts, inflammatory processes, or post-traumatic conditions. IMAGING FINDINGS: The MR imaging appearance of Parsonage-Turner syndrome is quite characteristic, with marked edema in the affected muscles of the shoulder, most commonly those innervated by the suprascapular nerve, although deltoid muscle can also be compromised. MR imaging of quadrilateral space syndrome may reveal fatty atrophy or edema isolated to the teres minor muscle. MR imaging of suprascapular nerve syndrome is established when edema or fatty changes of supraspinatus and/or infraspinatus muscle is present along with a cyst or ganglion in the spinoglenoid or suprascapular notch. CONCLUSION: MRI is a powerful diagnostic imaging tool in the diagnosis of entrapment neuropathies of the shoulder and underlying causes, thus excluding other possible causes of shoulder pain. Moreover, MRI may recognize active changes of denervation in muscle from chronic denervation muscle changes or “fatty atrophy” in isolation, and therefore it may change treatment and management.