Imaging description

The earliest detectable changes in denervated muscles in patients with Parsonage–Turner syndrome are diffusely increased signal on fluid-sensitive sequences such as short tau inversion recovery (STIR) or T2-weighted sequences and normal signal on T1-weighted images. After a few weeks in the subacute to chronic phase, the denervated muscle atrophies, seen as a reduction in muscle bulk and increased T1 signal due to fatty infiltration (Figure 9.1). MR imaging findings of quadrilateral space syndrome include atrophy of the teres minor and, less commonly, of the deltoid, which is seen as a reduction in muscle bulk and fatty infiltration with chronic compression.

Importance

No test is specific for the diagnosis of Parsonage–Turner syndrome and MR imaging must be interpreted in light of the patient's clinical history. In patients with quadrilateral space syndrome, MR imaging commonly shows no structural abnormality within the quadrilateral space but may reveal secondary features of denervation myopathy.

Typical clinical scenario

Parsonage–Turner syndrome is an uncommon, self-limiting disorder characterized by sudden onset of non-traumatic shoulder pain associated with progressive weakness of the shoulder girdle musculature. Quadrilateral space syndrome is characterized clinically by poorly localized anterolateral shoulder pain and is exacerbated by forward flexion, abduction, and external rotation of the humerus.

Differential diagnosis

Differential diagnosis includes intrinsic shoulder abnormalities such as rotator cuff tears, impingement syndrome, and labral tears.

Teaching point

MR imaging is the technique of choice in patients with shoulder pain and weakness, and it is sensitive for the detection of signal abnormalities in the shoulder girdle musculature related to denervation injury.