Pitfalls In Rotator Cuff Imaging

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Rotator Cuff Injury Causes and Treatment

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Intermediate or inhomogeneous signal in the cuff tendons are causes of diagnostic difficulty. Although the signal may be because of tendinopathy or partial tearing, artifacts such as magic angle phenomenon, inhomogeneous fat suppression, and partial volume averaging also may cause an increase in signal.

Magic angle phenomenon occurs on short TE sequences, such as PD sequences. Artifactually increased signal may be seen where the fibers of the cuff tendons are aligned at a 55-degree angle to the main magnetic field. At that angle there is T2 lengthening that results in focally increased signal. This artifact is recognized by its characteristic location where the tendon begins to slope downwards. The artifact is confirmed by comparison to T2 images that have a long TE and so do not show the artifact [1].

Rotator Cuff Magic Angle

Fig. 9. Internal impingement in 28-year-old patient. Following intra-articular injection of contrast material, fat-suppressed Tl-weighted oblique coronal image (A) demonstrates small partial-thickness articular surface tear (straight arrow) of supraspinatus tendon and tear of superior labrum (curved arrow). More posteriorly (B), high-signal contrast material leaks under the superior glenoid labrum, indicating type 2 superior labrum, anterior-to-posterior (SLAP) lesion (arrow). At arthroscopy, internal impingement was confirmed, and the tendon and labral lesions were debrided. H, humeral head.

Fig. 9. Internal impingement in 28-year-old patient. Following intra-articular injection of contrast material, fat-suppressed Tl-weighted oblique coronal image (A) demonstrates small partial-thickness articular surface tear (straight arrow) of supraspinatus tendon and tear of superior labrum (curved arrow). More posteriorly (B), high-signal contrast material leaks under the superior glenoid labrum, indicating type 2 superior labrum, anterior-to-posterior (SLAP) lesion (arrow). At arthroscopy, internal impingement was confirmed, and the tendon and labral lesions were debrided. H, humeral head.

The appearance of calcium on MRI can be deceptive. Calcifications in the cuff may appear dark or bright and may be misinterpreted as subacromial spurs or as tears. The presence of calcific tendinopathy is excluded easily by obtaining radiographs. In addition, bony changes associated with impingement, such as subacromial enthesophytes and sclerosis, and remodeling of the greater tuberosity, are appreciated more easily on radiographs than on MRI [10]. Whenever possible MRI studies should be read in conjunction with comparison radiographs.

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