Diagnostic ultrasound ( PDFDrive )

CHAPTER 24 The Shoulder 895
A
B
FIG. 24.30 Short-Axis Images of the Supraspinatus Tendon. (A) Artifactual hypoechogenicity of the supraspinatus tendon (arrows) may
simulate tendinosis or tear. (B) Correction of angle of insonation to be perpendicular to the tendon permits visualization of the normal intact
supraspinatus tendon (arrows).
PITFALLS IN SHOULDER
ULTRASOUND
Anisotropy is a common problem in diagnostic shoulder
ultrasound, but thankfully one that can be easily rectiied. It
consists of artifactual hypoechogenicity within a tendon caused
by scanning with the probe in a suboptimal angle with respect
to the tendon. As a highly organized linear structure, a tendon
relects ultrasound waves, efectively giving a normal echogenic
appearance when the angle of insonation is close to 90 degrees.
However, deviation from this angle can result in relection of
sound waves away from the transducer, leading to apparent
hypoechogenicity, which can be erroneously interpreted as
tendinosis or tearing. 37 his can be corrected by attention to the
angle of insonation of the tendon in question and by attempting
to visualize any pathologic inding in more than one plane (Fig.
24.30, Video 24.5).
here are several additional scanning pitfalls frequently
encountered by the inexperienced sonographer. Tears of the
anterior-most ibers of the supraspinatus are easily missed if
scanning does not extend anteriorly enough. One way to solve
this problem is to use the anatomic landmark of the long head
bicipital tendon as the starting point for scanning the supraspinatus
tendon, both in short and long axis.
In the hands of novice operators, chronic full-thickness rotator
cuf tears with echogenic granulation tissue may be confused
for intact, abnormal tendon. Careful evaluation with dynamic
compression, and diferentiation of bursal tissue from rotator
cuf tissue should be performed. In addition, inexperienced
operators may mistake the junction of the posterior supraspinatus
and anterior infraspinatus, where the tendon ibers overlap, as
pathology. Careful angling of the probe with respect to the long
axis of the ibers, and direct correlation to short-axis images
should ameliorate this misperception.
If the long head biceps tendon is not seen in the bicipital groove,
one should not automatically assume that the tendon is torn. It is
important to ensure that the transducer is perpendicular to the
tendon, as otherwise the tendon may appear artifactually hypoechoic
owing to anisotropy. he transducer should then be moved medially
to visualize the coracoid process, to look for a medially dislocated
tendon. Lastly, one should scan distally to the pectoralis junction
to see if the tendon has torn and retracted distally.
Sot tissue distortion by bony abnormality can cause confusion
during imaging and can be rectiied by referring to a concurrent
radiograph. 100 his is particularly the case in the setting of recent
trauma wherein an underlying fracture can cause considerable
distortion, especially if the greater tuberosity is involved.
As is the case for learning any skill, there is a learning curve
involved when performing diagnostic shoulder ultrasound.
Accuracy is lower when operators are unfamiliar with the
technique, but the learning curve plateaus between 50 and 100
cases, 101 which should be considered when undertaking this
examination for the irst time and when training and mentoring
other sonographers.
CONCLUSION
In conclusion, ultrasound is an accurate and cost-efective
technique for diagnosing sot tissue pathology at the shoulder
and is well tolerated by patients. Ultrasound confers many
advantages over MRI in the evaluation of the rotator cuf.
Adequate experience in this technique is important, in addition
to correlation with other imaging modalities when available.
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