An axial MRI scan of the shoulder acquired at multiple anatomical levels provides a detailed, slice-by-slice view of the joint, enabling precise evaluation of the rotator cuff tendons, labrum, biceps tendon, articular cartilage, bone marrow, and surrounding soft tissues. In clinical practice, axial sequences are a core component of shoulder MRI protocols because they align with the natural orientation of the humeral head within the glenoid fossa, making it easier to detect tears, impingement signs, instability findings, and degenerative changes. This guide explains key anatomy, common pathologies, and how radiologists and clinicians use axial images to inform diagnosis and treatment planning.
Fundamentals of Shoulder MRI Acquisition
MRI of the shoulder typically includes a combination of axial, sagittal, and coronal sequences, each optimized to highlight different tissue contrasts and anatomical landmarks. Axial images are acquired perpendicular to the long axis of the humerus, providing cross-sectional views that map the spatial relationship of articular surfaces and deep structures. T1-weighted sequences deliver excellent anatomic detail and signal characteristics similar to gross anatomy, while T2-weighted and intermediate-weighted sequences increase sensitivity for edema, inflammation, and fluid-filled lesions. Several pulse sequences may be used, including proton density–weighted, fat-suppressed, and gradient-echo or steady-state sequences, to improve visualization of specific tissues or pathology. Acquisition parameters, including slice thickness, gap, field of view, and matrix size, influence spatial resolution, signal-to-noise ratio, and the ability to assess fine anatomic detail.
Typical MRI Protocol Elements for the Shoulder
- Sequences: T1-weighted, T2-weighted (with and without fat suppression), proton density–weighted, gradient-echo
- Orientations: Axial, sagittal, coronal; oblique sequences aligned with tendon insertions when needed
- Coils: Dedicated shoulder or phased-array torso coils for optimal signal
- Contrast: Intravenous gadolinium is used selectively for evaluating capsular integrity, synovitis, or tumor
Key Structures Seen on Axial MRI
In axial MRI slices, the shoulder presents a layered anatomy that can be systematically assessed from superior to inferior and from articular surface to extra-articular soft tissues. Recognizing the normal appearance of each structure helps clinicians confidently identify deviations caused by injury, inflammation, or degeneration. Radiologists often correlate findings with clinical history and physical examination, because some morphologic features can be present without symptoms.
Articular Surfaces and Joint Space
The articular cartilage covering the humeral head and glenoid fossa appears as a thin, low-signal-intensity band on both T1- and T2-weighted images. Uniform joint space width and smooth contour indicate preserved cartilage, whereas focal thinning, fissuring, or irregularity suggests early osteoarthritis or post-traumatic changes. Bone marrow signal adjacent to the articular surface can provide indirect signs of subchondral remodeling or occult bone pathology.
Humerus and Glenoid Fossa
The humeral head appears as a rounded structure with intermediate to slightly high T2 signal in normal marrow, surrounded by a thin peripheral rim of low-signal subchondral bone. The glenoid fossa, part of the scapula, should be well corticated with a symmetric contour; subtle variations in shape may influence susceptibility to instability. Bone marrow edema or cystic changes can reflect stress reaction, impingement, or inflammatory conditions. Cortical breaches or focal bone lesions warrant further investigation to exclude tumor or infection.
Rotator Cuff Complex
The rotator cuff comprises four tendons—supraspinatus, infraspinatus, teres minor, and subscapularis—that converge to stabilize the humeral head. On axial images, the tendons insert along the greater tuberosity, and their integrity can be evaluated from the articular to the bursal surface. Normal tendons demonstrate homogeneous intermediate signal on T2-weighted images and relatively low signal on T1-weighted images. Tendon thinning, tendon retraction, high T2 signal internal to the tendon, and discontinuity are key findings in partial and full-thickness tears. Tendonosis or tendinosis may manifest as fusiform enlargement with intermediate signal and disorganized internal architecture, often without clear evidence of macroscopic tear.
Labrum and Capsule
The glenoid labrum is a fibrocartilaginous rim that deepens the socket and is evaluated best on sequences with high contrast between cartilage and soft tissue. Tears may manifest as irregular margins, flap-like displacements, or bucket-handle configurations, sometimes with associated instability signs. The joint capsule appears as a thin structure that should not significantly enhance or display nodularity in the absence of inflammation. Labral pathology and capsular laxity are important contributors to shoulder instability and should be carefully correlated with clinical symptoms and provocative testing.
Biceps Tendon and Intertubercular Sulcus
The long head of the biceps tendon traverses the intertubercular sulcus and is commonly assessed on axial images. Normal tendon signal is typically low on T1- and T2-weighted images, and the tendon should remain within the bicipital groove without substantial bowstringing. Tendon disorders include tendinitis, partial tearing, subluxation or dislocation out of the groove, and degenerative changes. Associated findings such as bone bruising or remodeling at the sulcus may indicate chronic instability or tendon pathology.
Common Pathologic Findings on Axial Images
Several common pathologic entities are reliably identified on axial MRI of the shoulder. Accurate interpretation of these findings often requires comparison across sequences and correlation with adjacent anatomy, as some lesions can mimic one another in appearance. In many cases, integrating axial views with sagittal and coronal reconstructions improves confidence in localization and characterization.
Rotator Cuff Tears
Full-thickness rotator cuff tears typically demonstrate complete loss of tendon continuity, with retraction of the tendon margins and often superior migration of the humeral head. Partial-thickness tears may appear as focal high-signal intensity that does not extend completely through the tendon thickness or as tendon surface irregularities. Indirect signs include fatty infiltration of the rotator cuff muscles and atrophy. The presence and size of the tear influence treatment decisions, with larger and chronic tears often associated with poorer functional outcomes without surgical repair.
Labral Tears and Instability-Related Changes
Labral tears, including SLAP (superior labrum anterior to posterior) lesions and Bankart lesions, can show abnormal morphology, contrast enhancement extending into the labral substance, or displacement. In instability scenarios, the relationship between the humeral head and glenoid can be evaluated with dynamic or stress images when available, although these are not always obtained. Hill-Sachs lesions and bony Bankart lesions represent osseous injuries associated with recurrent anterior instability; their size and location affect recurrence risk and treatment strategy.
Impingement and Associated Soft Tissue Changes
Evidence of impingement may include subacromial bursitis, tendinosis of the supraspinatus or infraspinatus, and partial articular-sided rotator cuff tears. Acromial morphology, such as the presence of a hooked acromion or reduced subacromial space, can be assessed on axial images and correlated with clinical impingement. Chronic impingement can lead to cuff tears and secondary changes in the acromioclavicular joint, which may also be evaluated on axial sequences.