Diagnostic ultrasound ( PDFDrive )

CHAPTER 23 Overview of Musculoskeletal Ultrasound Techniques and Applications 859
A
B
FIG. 23.4 Medial Head Gastrocnemius Tear From the Aponeurosis. (A) Long-axis image shows blunting and retraction of the medial head
gastrocnemius ibers (arrows) from the aponeurosis (*) with an associated hematoma (arrowheads). (B) Short-axis image shows effacement of
the normal gastrocnemius muscle (G) architecture and a hematoma of mixed echogenicity at the site of the tear from the aponeurosis (arrowheads).
S, Soleus muscle.
FIG. 23.5 Forearm Muscle Herniation. At the site of the palpable
abnormality, there is focal herniation of a portion of the pronator teres
muscle (PT) (arrows) through the muscle fascia (arrowheads). This patient
noticed a forearm bulge while weightlifting. U, Ulna.
standing, the area should be scanned with the patient reproducing
the relevant position where possible.
Muscle atrophy can occur in response to denervation or
chronic injury, for example, in the setting of a chronic complete
rotator cuf tear. Muscle atrophy is characterized on ultrasound
as a decrease in muscle bulk and a relative increase in echogenicity,
relecting replacement of muscle ibers with fatty tissue (Fig.
23.6). Comparison with adjacent muscles or the contralateral
side can assist in subtle cases. As a result of increased echogenicity,
the visibility of the central tendon at the myotendinous junction
is diminished, and there is a loss of normal pennate pattern. 14
TENDONS
Imaging the musculoskeletal system with ultrasound has built
on early success in evaluation of tendons, with initial reports of
Achilles tendon assessment. 15 Many tendons are ideally suited
to ultrasound evaluation, as they are supericial and require the
high-resolution imaging that ultrasound afords. Normal tendons
are composed of longitudinally oriented bundles of collagen
ibers, which give a highly organized echogenic linear ibrillar
or striated pattern on ultrasound when viewed in long axis (Fig.
23.7). In short-axis view, normal tendons are usually smooth
and ovoid in outline, with a homogenous stippled appearance,
representing the tendon ibers viewed en face. Some tendons,
such as the lexor and extensor tendons of the hand and wrist,
are invested in a synovial lined sheath, whereas others, such as
the Achilles tendon, are enveloped in a layer of loose areolar
tissue called a paratenon.
It is critically important to understand the concept of anisotropy
when performing the sonographic evaluation of tendons
(Fig. 23.8). Collagen bundles, because of their smooth parallel
organization within tendons, act as specular relectors, such that
sound waves are relected in a single direction. When these
specular relectors are imaged with ultrasound, if the angle of
insonation is not perpendicular to the tendon ibers, sound waves
will be relected away from the transducer, leading to the generation
of an image with artifactual hypoechogenicity within the
tendon. 16 his can be resolved by correcting the angle of insonation
to 90 degrees when an area of hypoechogenicity is observed.
he inding of focal persistent abnormal hypoechogenicity in a
second plane with optimized imaging adds further corroboration
to the observation of an apparent pathologic hypoechoic region.
Tendon injuries are usually caused by overuse and range from
tendinosis to complete tear. he term tendinosis refers to
intratendinous degeneration without tearing. Histologically,
tendinosis consists of tendon expansion and loss of clear demarcation
of collagen bundles, with increased mucoid ground substance
among collagen bundles. 17 here is noninlammatory ibroblastic
and myoibroblastic cellular proliferation. On ultrasound, tendinosis
appears as an area of hypoechogenicity, without discontinuity,
frequently associated with varying degrees of tendon
thickening (Fig. 23.9). Dystrophic calciication, and even
ossiication, can be seen within afected tendons. An additional
characteristic feature is the development of neovascularization,