"In ten years, Ultrasound will account for more than half of all soft tissue imaging studies"
Barry Goldberg, M.D, Thomas Jefferson University, Philadelphia
Dr. Jon Jacobson, professor or Radiology at the University of Michigan writes in Diagnostic Imaging (“Ultrasound takes on musculoskeletal MRI”) the comparative benefits of Ultrasound for musculoskeletal imaging:
- Sonography is capable of producing results similar to those of MRI when performed by an experienced examiner.
- MSUS Provides detailed depiction of superficial structures. It is also portable and less expensive.
- Interventional procedures such as joint aspiration can be guided with sonography.
- Dynamic examination of sonography may detect abnormalities that are present only with joint positioning not obtainable with MRI.
- MSUS is useful when MRI’s are contraindicated (metal implants, claustrophobia, etc).
- Superficial tendons and muscles can be easily depicted at high resolution. Sonography should be considered when a tendon abnormality is clinically suspected.
- MSUS allows differentiation between full-thickness and partial-thickness tendon tears with greater ease than MRI.
- MSUS sensitivity in diagnosing partial-thickness tears (in rotator cuff) is 93%.
- Tendons demonstrate a fine fibrillar echotexture by sonography and appear hyperechoic relative to muscle.
- One advantage of sonography over MRI is in the evaluation of biceps brachii longhead tendon Subluxation.
- Another abnormality that may be better depicted by sonography than by MRI is calcium hydroxyapatite crystal deposition, or calcific tendonitis.
- Another area producing promising results is the evaluation of ankle tendons, including the posterior tibial tendon. Although MRI may also be used to evaluate ankle tendon pathology, high-resolution sonography may demonstrate intrasubstance alterations and partial-thickness tears, which are difficult to resolve with standard MRI imaging.
- Another area of success is evaluation of the Achilles tendon. High-resolution sonography allows detection of an intact Plantaris tendon, which may be difficllt to identify with MRI imaging. Information regarding the Plantaris tendon and the torn Achilles tendon approximation can assist the surgeon in deciding between surgical and conservative treatment.
- When a patient presents with a painful and erythematous extremity, it may be difficult to differentiate between cellulitis, septic effusion, and soft-tissue abscess on clinical grounds alone. Both MRI and sonography can be used for this purpose. Additionally, sonography has the advantage of mobility and availability.
- Immediate aspiration can be guided with sonography to confirm the diagnosis of infection.
- Evaluation of a soft-tissue infectious process adjacent to an orthopedic device or hardware is possible with sonography, but not with MRI imaging due to the presence of metal. It allows easy visualization of an adjacent joint effusion or soft-tissue fluid collection.
- Certain foreign bodies, such as wood, cannot be identified by radiography, but are easily detected with sonography. Wooden bodies as small as 2.5 mm have been successfully detected.
- Sonography can accurately locate a soft-tissue foreign body, indicate its location by marking the overlying skin, and provide guidance for surgical removal.
- In the evaluation of carpal tunnel syndrome, causes for nerve compression such as ganglion cysts and tenosynovitis can be identified. Both MRI and sonography are effective in the diagnosis of carpal tunnel syndrome.
- When soft tissue mass is identified, sonography can determine if the mass is cystic or solid, and demonstrate its relation to adjacent structures.
- There are two scenarios in which sonography can be used in place of MRI when evaluating a soft tissue mass: ganglion cyst of the wrist, and Baker cyst of the knee. MRI and sonography have been shown to be equally effective in diagnosing the wrist ganglia.
- Sonography is also useful in excluding other causes for palpable wrist mass such as paratendonitis or aneurysm.
- Sonography can confirm the presence of a cystic mass between the semimembranosus and the medial head of the gastrocnemius tendons.
- Sonography can determine if the Baker cyst is complicated from hemorrhage or has leaked into the adjacent soft tissues, as can MRI, which should be used if the patient will undergo surgery.
- Sonography has demonstrated its capability of producing results at least equivalent to those attained by MRI imaging in a range of musculoskeletal disorders. While its primary handicap is operator dependence, this can be minimized with proper training and standardized techniques.