Teres Minor Denervation Injury

Coronal T2 MR image with fat suppression demonstrates abnormal high T2 signal intensity within a portion of the teres minor. No mass was seen at the supraspinatus fossa.

Facts: MRI in Denervation Injury

• MR change of T1 and T2 prolongation can be seen as early as within 15 days after complete skeletal muscle denervation
• Initial stage of change due to denervation is increased extracellular water content and decreased muscle fiber volume
• Most chronic stage of change occurs after 1 year of injury. This is seen as atrophy and fatty replacement, which are irreversible
• There may be no change in signal intensity if denervation is partial or there is a collateral motor nerve innervation

MR Findings

• Signal change within the muscle in a diffuse and homogeneous pattern
• Adjacent subcutaneous fat and fascial layers typically are unaffected (different from trauma, inflammation or neoplasm)
• Distribution of abnormality can help identify the nerve injured:

Both supra- and infraspinatus involved --> suprascapular nerve above the supraspinatus fossa

Infraspinatus only --> suprascapular nerve below the supraspinatus fossa

Anterior deltoid --> axillary nerve (anterior branch)

Teres minor --> axillary nerve (posterior branch)

Reference:

Sallomi D, Janzen DL, Munk PL, Connell DG, Tirman PFJ. Muscle denervation patterns in upper limb nerve injuries: MR imaging findings and anatomic basis. AJR 1998; 171:779.