Inflammation is the body’s natural response to injury or infection. Ultrasound, a non-invasive imaging technique, visualizes internal body structures in real-time, including changes associated with inflammatory processes. It is a valuable tool for healthcare providers to assess and monitor inflammation within various tissues and organs.
How Ultrasound Works
Ultrasound imaging relies on high-frequency sound waves to create pictures of structures inside the body. A transducer sends these sound waves into the body; when they encounter tissues, some waves reflect back as echoes. The transducer receives these echoes, converting them into electrical signals that a computer processes to form a real-time image.
Tissue appearance on ultrasound is determined by its ability to reflect sound waves, known as echogenicity. Structures that produce no echoes, like simple fluid, appear black (anechoic). Tissues producing fewer echoes than surrounding areas appear darker (hypoechoic), while those reflecting more sound waves appear brighter (hyperechoic). These varying degrees help distinguish tissue types and identify abnormalities.
General Signs of Inflammation on Ultrasound
Inflammation presents with characteristic appearances on ultrasound, reflecting underlying physiological changes. Swelling or edema, a common sign, appears as hypoechoic (darker) areas due to fluid accumulation within affected tissues. This fluid often results in indistinct tissue planes.
Increased blood flow, or hyperemia, is another indicator detected using color or power Doppler ultrasound. This displays increased color signals within the inflamed region. This heightened vascularity delivers more immune cells and healing factors to the site of injury or infection.
Fluid collections, such as effusions or abscesses, also signal inflammation. Effusions, found in joints or body cavities, typically appear anechoic (black) or as complex fluid collections with internal echoes. Abscesses, localized pus collections, can appear as hypoechoic or anechoic fluid collections, sometimes with internal debris or gas bubbles.
Inflamed tissues may also exhibit changes in texture and echogenicity. They can appear thickened, irregular, or have an altered echotexture compared to healthy surrounding tissue. These visual cues aid in identifying inflammatory processes.
Ultrasound Appearance in Specific Conditions
The general signs of inflammation manifest uniquely across various specific conditions, providing distinct diagnostic patterns on ultrasound. In tendinitis and tenosynovitis, inflammation of a tendon or its surrounding sheath, ultrasound typically reveals tendon thickening and hypoechoic changes within the tendon. Fluid accumulation within the tendon sheath, appearing anechoic or hypoechoic, is also frequently observed, often accompanied by increased vascularity detected with Doppler.
For inflammatory arthritis, such as rheumatoid arthritis or gout, ultrasound can show synovial thickening, the thickening of the joint lining. Joint effusions, or fluid within the joint space, are commonly seen. Increased Doppler signals within the inflamed synovium indicate active inflammation, while in gout, hyperechoic urate crystal deposits may be visible within the joint or tendons.
When evaluating appendicitis, an inflamed appendix typically appears as a non-compressible, thickened tubular structure, often with a diameter greater than 6 millimeters and a wall thickness exceeding 3 millimeters. Periappendiceal fluid and increased blood flow within the appendix wall, visible on Doppler imaging, are additional indicators. Surrounding fat tissue may also appear hyperechoic and stranding due to inflammation.
In cellulitis, a widespread bacterial infection of the skin and subcutaneous tissue, ultrasound often shows diffuse thickening of the skin layers and hyperechoic changes in the subcutaneous fat. This can present as a “cobblestone pattern” due to fluid accumulation. Abscesses may also be present, appearing as well-defined hypoechoic or anechoic fluid-filled areas, sometimes with internal debris or gas, and may show increased surrounding vascularity on Doppler.
Benefits and Limitations of Ultrasound for Inflammation
Ultrasound offers advantages when assessing inflammation. Its real-time imaging allows for dynamic evaluation of tissues and blood flow. The technique is non-invasive, involving no needles, incisions, or ionizing radiation, making it a safe option for repeated examinations.
Ultrasound is relatively inexpensive and widely accessible compared to other imaging methods. It can also guide procedures, such as fluid aspirations or injections, by providing direct visualization of the target area. Visualizing increased blood flow and fluid changes in real-time provides immediate information for clinicians.
Despite its benefits, ultrasound has limitations. Its effectiveness depends on the operator’s skill and experience. Depth of penetration is limited, making it challenging to visualize deep organs or structures obscured by bone or gas. While ultrasound can detect inflammation, it may not always distinguish between different causes without additional clinical information or other diagnostic tests. Therefore, ultrasound is often part of a broader diagnostic process, not a standalone tool for definitive diagnosis.