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Presentation1, radiological imaging of artifact and pitfalls in shoulder joint at mri.
This document discusses various normal anatomical variations and artifacts that can be mistaken for pathology on shoulder MRI images. It describes variations that can be seen in tendons like the biceps and rotator cuff, ligaments, labral structures, bone structures, and bone marrow. Specifically, it notes variations in tendon bifurcation and vascular structures, subtle differences between tendons in the rotator cuff, variants of ligaments and labral structures like the sublabral foramen, and normal anatomical grooves and depressions in bones that should not be confused with defects or lesions. Positioning artifacts are also discussed. The document aims to help radiologists avoid misdiagnosing these normal variants as pathological conditions.
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Presentation1, radiological imaging of artifact and pitfalls in shoulder joint at mri.
- 1. Artifacts and pitfallsin shoulder magnetic resonance imaging. Dr/ ABD ALLAH NAZEER. MD.
- 2. TENDONS: Long head ofthe biceps brachii The vincula of the biceps tendon (synovial bands attaching to the biceps within the tendon sheath) may be seen within the bicipital groove. Blood vessels can also be depicted in the bicipital groove. Bifid or duplicated biceps brachii tendon constitutes a normal variation, it may be mistaken for longitudinal split tendon tears.
- 3. Biceps vincula (mesotendon).The biceps tendon obtains its blood supply from a mesotendon (arrow), also called vinculatendinum
- 4. Vessels adjacent tothe long head of the biceps tendon (arrows).
- 5. Coronal fat-suppressed T2-weightedimage shows thin, high-signal- intensity linear structures (arrows) in supraspinatus tendon and muscle. These are blood vessels that should not be misinterpreted for tears.
- 6. Sagittal fat-suppressed T2-weightedMR image shows dilated veins (arrow) in spinoglenoid notch. These should not be mistaken for paralabral cysts.
- 7. Bifid biceps tendon(arrow).
- 8. Rotator cuff The supraspinatustendon usually inserts into the greater tubercle of the humerus. However, rarely it may be ectopically inserted into the bicipital groove. Mochizuki et al. have demonstrated that the supraspinatus tendon may also insert into the lesser tuberosity of the humerus. Also, Clark et al. have demonstrated the difficulty in separating the fibers of the supraspinatus and infraspinatus tendons. In some cases, one just cannot say exactly which tendon has a tear, but this should not be a source of distress.
- 9. Frequently, in thearea of the insertion, one can hardly determine where the supraspinatus tendon ends and where the infraspinatus tendon starts.
- 10. Coronal (A) andabduction external rotation (B) fat-suppressed T1-weighted MR arthrograms show rotator cable (arrow) underlying supraspinatus tendon.
- 11. A magic angleartifact may also occur in the supraspinatus tendon at short TE spin echo sequences; likewise seen in the intracapsular long head of the biceps brachii. In such cases, T2-weighted sequences are very useful to distinguish between magic angle artifact and rotator cuff tendinosis or partial tendon tear). The area of bright signal within the tendon does not persist or is decreased on T2-weighted images with longer TE.
- 12. Magic angle androtator cuff. Increased signal in the supraspinatus tendon at short TE sequence.
- 13. Magic angle androtator cuff. Coronal PD and T2-weighted images of the supraspinatus insertion. At left, increased signal on the short TE sequence (arrow), which is not seen on the long TE sequence at right (arrow).
- 14. Another pitfall involvingthe supraspinatus tendon is the small sulcus of uncovered bone located between the supraspinatus insertion and the joint cartilage. The presence of this sulcus is important because this small area of exposed bone should not be mistaken for a chondral articular surface injury or even a partial tear. A small sulcus between the osseous insertion of the supraspinatus and the articular cartilage (arrow) is a normal finding.
- 15. Glenohumeral ligament andcapsular variants The MGHL may be thickened (a cord-like pattern) or thinned. The association of thickened MGHL and absent anterosuperior labrum is called a Buford complex. Compensatory thickening of the MGHL is due to the absent labrum. The frequency of Buford complex approximates to 1.5% of shoulders. The Buford complex should not be mistaken for detachment of the anterior superior labrum.
- 16. Thickened MGHL (arrow)and absent anterosuperior labrum (Buford complex).
- 17. Axial fat-suppressed T1-weightedMR arthrogram shows cordlike middle glenohumeral ligament in front of superior glenoid rim with absent labrum, representing Buford complex (arrow).
- 18. Sagittal fat-suppressed T2-weightedMR images show normal superior (black arrow) and middle (white arrow, A) glenohumeral ligaments (A) and anomalous bifid middle glenohumeral ligament (arrow, B).
- 19. Axial fat-suppressed T2-weightedMR image shows corrugated appearance of attachment of inferior glenohumeral ligament on humeral neck (arrow).
- 20. Axial fat-suppressed T2-weightedMR image shows thickened posterior glenohumeral ligament adjacent to normal labrum (arrow). This anomaly can be mistaken for labral tear.
- 21. LABRAL VARIANTS Anatomic variationsof labral form and contour are commonly found. Usually, such variations occur in the superior half of the labrum, close to the insertion of many of the stabilizing capsular structures, and may easily mistaken for labral or capsular pathology. The sublabral foramen is an anatomic variation located in the anterosuperior labrum, where it is detached from the anterior glenoid margin, allowing for communication between the glenohumeral joint and the subscapular recess. It is important to recognize such a variation at MR arthrography, as it may be misinterpreted as anterior extension of a SLAP tear.
- 22. The sublabral foramen(arrows) is an anatomic variation and sometimes it may be not easily differentiated from labral tear.
- 23. Coronal T2-weighted MRimage shows smooth, thin defect at base of superior labrum consistent with sublabral recess (arrow).
- 24. Axial fat-suppressed T1-weightedMR arthrogram shows defect (arrow) at base of anterior superior labrum, consistent with sublabral foramen.
- 25. Axial fat-suppressed T1-weightedMR arthrogram shows normal gap (arrow) between superior labrum and middle glenohumeral ligament that should not be mistaken for tear.
- 26. Axial fat-suppressed MRarthrogram shows normal intermediate-signal-intensity cartilage (arrow) at interface between anterior labrum and glenoid fossa.
- 27. Coronal MR arthrographyT1-weighted sequence showing a normal sulcus in the region of the biceps-labral complex (arrow), which is typically parallel to the glenoid (A). In SLAP tears, the signal alteration extends towards the substance of the superior labrum (B).
- 28. JOINT RECESSES ANDBURSAE The subscapular recess is an extension of the glenohumeral joint located on the posterior and anterosuperior aspects of the subscapularis tendon, typically just below the coracoid process. Therefore, it may be confused for the subcoracoid bursa. The subscapular recess freely communicates with the glenohumeral joint via various possible synovial foramina located between the glenohumeral ligaments. It is should be highlighted that, in healthy shoulders, there is no communication between the glenohumeral joint and the subcoracoid bursa. However, a communication between the subacromial-subdeltoid bursa and subcoracoid bursa might be present.
- 29. Subscapular recess (A)versus subcoracoid bursa (B). The subscapular recess communicates with the glenohumeral joint (short arrow). The subcoracoid bursa is located anteriorly to the subscapular tendon and inferiorly to the coracoid process, but does not communicate with the joint cavity. Coracoid process (arrowheads).
- 30. POSITIONAL VARIATIONS The supraspinatusand infraspinatus tendons are best imaged with the patient’s shoulder placed in external rotation. Such tendons remain out of the standard at coronal and sagittal imaging as the humerus is internally rotated or externally rotated in excess. In such a condition, the increased tendons overlap may preclude the diagnosis of possible injuries, because the supraspinatus tendon may appear discontinuous. Also, if there is an exaggerated internal rotation, there may be a false subscapularis tendon thickening or artifactual signal abnormality from the MGHL and capsular structures. Such positioning may also result in abnormal signal intensity of the supraspinatus and infraspinatus, probably due to a magic angle effect.
- 31. Exaggerated internal rotationon the image A, simulating subscapularis tendon thickening (short arrow). Certainly, the tendon is normal (long arrow) with external rotation (B).
- 32. ACROMION Based on shape,the acromion process has been classified into four types, namely, type 1 (straight or flat); type 2 (curved); type 3 (hooked); type 4 (inverted). This fourth type has lately been added and represents a convex or upward pointing undersurface. These morphological acromial variations may be viewed by using either scapular Y- view radiographs or sagittal oblique and coronal oblique MRI sequences.
- 33. The figures representeach acromion type.
- 34. The os acromialeforms a pseudoarticulation with the base of the acromion through the fibrous tissue, periosteum, cartilage or synovium. A second “acromioclavicular” joint may be seen on images, where the os acromiale is seen articulating with the clavicle. It is important to identify an os acromiale because it plays a role in the development of shoulder impingement symptoms due to inferior displacement at deltoid contraction. Degenerative changes in this pseudoarticulation may occur across the synchondrosis or in association with acromioclavicular degeneration
- 35.
- 36. Axial T1-weighted MRimage demonstrates the acromioclavicular joint and the os acromiale (white arrow). Acromion (A) and clavicle (C).
- 37. Coronal fat-suppressed T1-weightedMR arthrogram shows normal low- signal-intensity attachment of deltoid tendon along inferior lateral aspect of acromion (arrow). Subacromial enthesophyte can also occur in this location.
- 38. HUMERUS A normal grooveis frequently found at the posterior aspect of the humerus near the junction of the head and proximal diaphysis, representing a potential pitfall at axial MR imaging, and should not be mistaken for a Hill-Sachs lesion. Such a distinction becomes important in patients with a history of glenohumeral instability, considering that the presence of a Hill-Sachs lesion might warrant surgical treatment. Usually, Hill-Sachs defects are visible on the uppermost axial images of the humerus, superolaterally at 5 mm from the top of the humeral head. The normal anatomic groove of the humerus usually lies at 20 to 30 mm from the superior humeral head and is more medial and posteriorly positioned on axial images. Depth and width of the defect are not considered to be reliable indicators for its differentiation
- 39. Normal groove inthe posterior aspect of the humeral head (A). Hill- Sachs defects are visible on the uppermost axial sections (B).
- 40. Normal humeral headversus Hill-Sachs lesion. (A) On the axial T2 gradient echo weighted MR image, there is a slight flattening of the posteroinferior surface of the humeral head (arrow), which is a normal finding. (B) Axial fat saturated T2-weighted MR image obtained at the level of the coracoid process (arrowhead, B) typically shows a Hill-Sachs defect (arrow) in a patient with history of anterior shoulder dislocation.
- 41.
- 42. GLENOID The shallow glenoidcavity provides increased range of motion of the glenohumeral joint at the cost of stability. This stability is achieved by the surrounding structures, particularly the glenohumeral ligaments, labrum, and rotator cuff. Some imaging abnormalities and variations of the glenoid may be present. At the central region of the glenoid, there is an area of thickened subchondral bone (tubercle of Ossaki) with thinned overlying cartilage. It should not be mistaken for an area of chondral damage or loss. On the other hand, in this equivalent area, a smooth focal full thickness cartilage defect without thickening of the underlying bone may be seen as a normal variant and should not be confused with chondromalacia
- 43. Tubercle of Ossaki.Area of focal subchondral bone thickening with thinned overlying cartilage (arrows).
- 44. Axial (A) andsagittal (B) fat-suppressed T1-weighted MR arthrograms show depression (arrow) in central glenoid cavity devoid of cartilage. Finding represents bare area of glenoid cavity, which is normal variant.
- 45. Axial (A) andsagittal (B) fat-suppressed T1-weighted MR arthrograms show depression (arrow) in central glenoid cavity devoid of cartilage. Finding represents bare area of glenoid cavity, which is normal variant.
- 46. Axial images atthe level of the inferior glenoid demonstrate the normal triangular type glenoid rim shape (A), the rounded " Lazy J " type glenoid rim shape (B) and the deltoid glenoid rim shape (C) (white arrowheads).
- 47. Axial MR imageat the level of the middle glenoid shows a slight retroversion of the normal glenoid.
- 48. BONE MARROW Heterogeneous signalintensity from the bone marrow heterogeneous signal is typically observed in the region of the humeral head and neck. In adult patients, red marrow may be physiologically seen below the physeal scar with slightly hypointense signal at T1- weighted images. Red marrow should not be confused with marrow infiltrative processes, nodules or tumors. In infiltrative processes, the marrow signal becomes markedly low, hypointense to the muscle.
- 49. Normal bone marrowstriations.
- 50.