Age / Sex : 57 / F

Chief complaint : Rt. shoulder pain

What is the structure indicated with arrows?


Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).


Courtesy : 정준용 (Joon-Yong Jung), 서울성모병원 (Seoul Saint Mary’s Hospital)

Ectopic Insertion of the Pectoralis Minor Tendon

Discussion

Findings:

[MRI]

Oblique sagittal T2-weighted images show pectoralis minor tendon slip passing over coracoid process and running underneath supraspinatus muscle, while main portion of pectoralis minor tendon inserts into anterior aspect of coracoid process.

Differential Diagnosis:

Discussion:

Most pectoralis minor tendons insert into the superomedial aspect of the coracoid process. However, in a cadaveric study, described three types of attachment variations of the pectoralis minor tendon, and about 15% of the cadavers showed ectopic insertion of the pectoralis minor tendon (EIPMT) passing over the coracoid process.

 Since that report, several studies have found EIPMT incidence rates of 9.6–16%. However, this anatomical variation has attracted little attention from radiologists regardless of the high incidence. The clinical significance of EIPMT remains obscure, but several studies have shown its association with subacromial or subcoracoid impingement and shoulder stiffness as in adhesive capsulitis.

In addition, the importance of preoperative detection of EIPMT in patients with a rotator cuff tendon tear because it can be a possible obstacle to retract the supraspinatus tendon upon immobilization, leading to tension on the repaired tendon. Therefore, a preoperative evaluation for EIPMT could be important for patients undergoing rotator cuff tendon repair.

US allows for a dynamic study to evaluate EIPMT but has disadvantages of being poorly objective and operator dependent. In turn, MR arthroscopy has an advantage to demonstrate EIPMT easily but may fail to detect partial EIPMT (a portion of the tendon has a normal insertion into the coracoid process and another portion has an anomalous insertion. In addition, the extra-articular portion such as the subcoracoid area cannot be evaluated because of fat suppression.

References:

1. Ectopic Insertion of the Pectoralis Minor Tendon: Inter-Reader Agreement and Findings in the Rotator Interval on MRI “Korean J Radiol 15(6), Nov/Dec 2014”


2. Pectoralis minor tendon in the rotator interval: arthroscopic, magnetic resonance imaging findings, and clinical significance “J Shoulder Elbow Surg (2015) 24, 848-853”