Diagnostic ultrasound ( PDFDrive )

858 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
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FIG. 23.2 Normal Muscle. (A) In short-axis view a normal vastus lateralis (VL) muscle demonstrates a speckled or “starry sky” appearance
(arrows). (B) In long-axis view the normal muscle demonstrates a pennate appearance (arrows). F, Femur; VI, vastus intermedius.
ultrasound pattern of muscle is typically feathery, or pennate,
with iber orientation usually directed along the long axis of the
muscle. In the short-axis view, the muscle ibers demonstrate a
speckled appearance (Fig. 23.2). Fibers typically converge to the
myotendinous junction and the muscle tapers in diameter at
this point (Videos 23.1 and 23.2). A thin layer of fascia surrounds
the muscle unit, separating it from adjacent muscles and
subcutaneous fat. Muscle is usually overall hypoechoic, with
more echogenic internal linear interfaces generated by the
perimysium.
Muscle injuries of diferent grades can be identiied with
ultrasound. 11 A grade I injury is a minor strain and is depicted
on ultrasound as just minimal iber elongation and hypoechogenicity,
but without detectible discontinuity. Ultrasound is less
sensitive than MRI to these minor grades of injury, which are
usually treated conservatively. 12 A grade II injury is a partial tear.
Fiber discontinuity is seen, with a focal anechoic or hypoechoic
gap, usually illed by more echogenic hematoma. Gentle probe
pressure can demonstrate muscle ibers loating freely within
luid and hematoma, referred to as the “bell-clapper” sign. At
the most severe end of the spectrum of muscle injury is a grade
III injury, or complete tear (Fig. 23.3). In the case of a grade III
injury, the muscle is completely interrupted with retraction of
the muscle ends and an interposed gap, which should be measured.
A large hematoma is expected in association with a complete
tear.
A distinct form of muscle injury that deserves special mention
is the avulsion of a muscle from its aponeurosis, a pattern of
injury particularly common in the calf in the clinical spectrum
of “tennis leg” (Fig. 23.4). In this injury the medial gastrocnemius
muscle tears away from the aponeurosis with the underlying
soleus muscle. Fluid and hematoma may dissect along the
aponeurotic plane and there may be some retraction of the medial
gastrocnemius. his usually occurs during forceful plantar lexion
FIG. 23.3 Muscle Tear. Long-axis image of the medial groin region
demonstrates hypoechoic luid (arrows) at the pubic symphysis (P) origin
of the adductor muscles, consistent with a grade III muscle tear.
during sports, for example, in a forceful lunge in tennis. his
injury may be accompanied by a plantaris tendon tear.
Symptomatic myofascial defects lend themselves well to
ultrasound evaluation. In this injury a defect in the muscular
fascia allows herniation of muscle ibers, leading to a palpable
and oten painful mass (Fig. 23.5). In some cases, the patient
may have associated neuropathy resulting from compression of
adjacent nerves. 13 he mass may be more apparent to the patient
during certain movements and activities that lead to muscle
contraction, and these can be reproduced during scanning to
assist in diagnosis. On ultrasound imaging, focused evaluation
of the region of concern reveals focal bulging of muscle ibers
through the otherwise smooth fascia. If this is equivocal or the
patient reports symptoms only in certain positions such as