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MD Consult: Books: Goldman: Cecil Medicine: ULTRASONOGRAPHY

Goldman: Cecil Medicine, 23rd ed.

Copyright © 2007 Saunders, An Imprint of Elsevier

ULTRASONOGRAPHY

In ultrasound imaging, sound waves are pulsed through tissues to obtain an image that can localize and characterize pathology. Through the years, resolution has increased markedly. Portable scanners are also being used, especially by nonradiologists. These units are less expensive. They are adequate for injections and for detection of fluid collections and tenosynovitis, but they do not provide the detailed anatomy of their high-end counterparts.

Ultrasound provides a less expensive, noninvasive method to visualize joint structures such as tendons, ligaments, fibrocartilage, muscles, and soft tissue masses without the use of ionizing radiation. Areas of pain and swelling can be scanned in real time with the opposite side for comparison. Fluid within tendon sheaths can be easily assessed. Fluid, blood, pus, and mucin in ganglia, cysts, bursae, hematomas, seromas, and abscesses can be differentiated from solid masses based on echogenicity ( Fig. 279-3 ). Areas around metallic hardware or other implants are easily assessed for such masses without the artifact that might limit MRI or CT evaluation.

FIGURE 279-3  Knee ganglion demonstrated by magnetic resonance imaging and ultrasonography. A, A fat-suppressed T2-weighted axial magnetic resonance image of the knee demonstrates a high-signal-intensity mass in the posterior aspect of the knee. Without intravenous gadolinium to show the enhancement pattern, it is difficult to determine whether the mass is cystic or solid. B, An ultrasound image demonstrates that the mass is hypoechoic, a finding consistent with a ganglion.

Hypervascularity is a component of inflammatory joint disease and angiofibroblastic response in tendons that can be assessed by Doppler imaging, a sonographic method that assesses vascular flow. This information can be used for diagnosis and assessment of therapeutic response and to identify locations for injections of anesthetic agents or steroids.

Ultrasound can demonstrate dynamic properties of tendons and other structures. The real-time capability allows for identification of subluxation and impingement, pinpointing causes of pain with certain movements. Ultrasonography is a quick and inexpensive method to perform accurate aspirations and injections of joints and soft tissue structures such as tendon sheaths and bursae. Areas of hydroxyapatite crystal deposition disease can be aspirated and injected.

Ultrasound is an operator-dependent technique with a steep learning curve. It can be time-consuming for the operator scanning the patient. Some important joint structures are in sonographically inaccessible areas, such as those obscured by bone. This includes portions of the menisci and the cruciate ligaments of the knee, the labra of the hip and shoulder, and some portions of hyaline cartilage that are more easily seen with MRI. Sonography does not allow for evaluation of bone marrow pathology or global assessment of a joint, but it can be helpful for targeted diagnostic problems, as outlined earlier.

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