Understanding Shoulder MRI
Magnetic Resonance Imaging, or MRI, is a non-invasive imaging technique providing detailed internal views. It uses strong magnetic fields and radio waves to generate cross-sectional images of organs, soft tissues, and bone. For the shoulder, MRI effectively captures details of its anatomy, including muscles, tendons, ligaments, and cartilage.
An MRI machine creates a powerful magnetic field, aligning the water molecules within the body’s tissues. Short bursts of radio waves are then emitted, temporarily knocking these aligned molecules out of position. When the radio waves are turned off, the water molecules relax back into alignment, releasing energy signals that are detected by the MRI scanner. Different tissues release energy at varying rates, allowing a computer to translate these signals into distinct, highly detailed images of the shoulder’s internal structures.
MRI offers superior soft tissue visualization compared to X-rays or CT scans, which primarily image bone. Its ability to differentiate soft tissues helps doctors identify subtle injuries, inflammation, or diseases within the shoulder joint. It helps locate and characterize abnormalities not visible with other imaging.
Common Conditions Revealed by Shoulder MRI
A shoulder MRI provides a comprehensive view, detecting conditions affecting joint stability and function. Common findings include rotator cuff tears, involving damage to one or more of the four tendons that stabilize the shoulder and enable arm movement. MRI can distinguish between partial tears (portion damaged) and full-thickness tears (completely severed), often showing fluid accumulation or tendon retraction.
Labral tears are also frequently diagnosed by MRI. The labrum is a cartilage rim that deepens the shoulder socket, helping hold the arm bone in place. MRI identifies types of labral injuries, such as SLAP (Superior Labrum Anterior to Posterior) tears, occurring where the biceps tendon attaches, or Bankart lesions, often associated with shoulder dislocations.
Inflammatory conditions like tendinitis and bursitis are apparent on MRI scans. Tendinitis involves tendon inflammation, such as biceps tendinitis in the front of the shoulder. Bursitis is inflammation of bursae, small fluid-filled sacs cushioning bones, tendons, and muscles around joints; MRI can show fluid accumulation and bursa thickening.
MRI can assess osteoarthritis, a degenerative joint disease, and other cartilage damage. The scan shows thinning or erosion of articular cartilage covering bone ends, bone spurs (osteophytes), and bone marrow edema, indicating joint degeneration. This aids in understanding cartilage loss and joint space narrowing.
MRI can reveal impingement syndrome, where tendons or bursae are compressed in a narrow shoulder space. The scan may show inflammation or swelling of the supraspinatus tendon or subacromial bursa, indicating compression under the acromion. It also identifies structural abnormalities contributing to impingement.
While X-rays are often first for fractures, MRI excels at detecting subtle or occult fractures not visible on plain X-rays, especially stress fractures. It shows bone marrow edema, an early sign of bone injury before a distinct fracture line is evident. This sensitivity is useful for diagnosing injuries causing persistent pain without clear X-ray findings.
MRI can identify abnormal growths or signs of infection within shoulder bone or soft tissues. It differentiates between benign and malignant tumors based on signal characteristics and shows fluid collection, inflammation, or bone destruction indicative of infection like osteomyelitis. This allows for precise localization and characterization of these less common but serious conditions.
Preparing for a Shoulder MRI
Preparing for a shoulder MRI involves steps for patient safety and image quality. Patients must remove all metal objects before entering the MRI suite, including jewelry, watches, hairpins, or clothing with metal. The strong magnetic field can interfere with metal, potentially causing injury or distorting images.
Patients should inform medical staff about any internal medical implants or devices. Those with pacemakers, certain artificial joints, cochlear implants, or aneurysm clips may not undergo an MRI due to magnetic field interaction. Some newer implants are MRI-compatible, but verification is necessary.
Sometimes, a contrast dye (typically gadolinium) might be injected intravenously to enhance tissue or abnormality visibility. If used, kidney function may be checked for safe dye excretion. Patients with claustrophobia should discuss it with their doctor, as medication may be prescribed to help them relax during the scan.
During and After a Shoulder MRI
During a shoulder MRI, the patient lies still on a movable table that slides into the tube-shaped MRI machine. The technologist provides headphones or earplugs to minimize the loud knocking or tapping noises produced by the machine. Communication with the technologist is maintained through an intercom, allowing the patient to speak if needed.
The scan typically lasts 30 to 60 minutes, depending on images required. Remaining still throughout the procedure is important for clear, high-quality images. Patients generally experience no discomfort, though some may feel a slight warming sensation in the scanned area.
Immediately after the shoulder MRI, there is usually no recovery time unless sedation was administered. Patients can typically resume normal activities. A radiologist, a doctor specializing in interpreting medical images, reviews the MRI images and prepares a detailed report. This report is sent to the referring healthcare provider, usually within a few days, who will discuss findings and next steps with the patient.