Diagnostic ultrasound ( PDFDrive )

1930 PART V Pediatric Sonography
At one time, we performed ultrasound in severe cases of DDH
ater casting through a window cut in the cast posteriorly. Now,
cross-sectional imaging with CT or magnetic resonance imaging
(MRI) is done ater casting. he localizer CT ilm enables the
technologist to select the appropriate level to assess hip position
with attention to keeping the radiation dose low. MRI is increasingly
used and gives no ionizing radiation, although its high
cost and limited availability are disadvantages. 43 Our MRI
protocols include T2-weighted images in axial and coronal
planes. 44 Vascularity of the femoral head ater reduction can be
evaluated by adding contrast to the examination. 45
Avascular necrosis of the femoral head is a recognized
complication of DDH treatment devices. Both color and power
Doppler ultrasound have been used to assess the vascularity of
the femoral head during treatment. Because of the microvascular
architecture in the cartilage canals, power Doppler sonography
is thought to have the best potential. Normal hips show a radial
pattern of low from the center of the unossiied head. he central
collection of vessels is the precursor of the ossiication center
and is seen before the center is apparent on radiographs. Bearcrot
and colleagues 46 reported that diminished low can be demonstrated
when the hip is placed in wide abduction, compressing
the medial circumlex artery. his may correlate with development
of avascular necrosis, and thus assessment of low has been
proposed as an aid in determining a safe abduction position for
treatment. he examination is technically diicult and currently
performed primarily in the research arena. Magnetic resonance
imaging has become the preferred method for diagnosis of
avascular necrosis. 45
OTHER PEDIATRIC
MUSCULOSKELETAL ULTRASOUND
APPLICATIONS
In pediatric musculoskeletal sonography, knowledge of the normal
appearance of cartilage, sot tissues, and developing osseous
structures is essential. Use of a high-frequency linear transducer
is advised, and comparison to the contralateral unafected side
is recommended. he focal zones should be over the area of
interest with the appropriate depth, and gain should be optimized
for the tissues scanned. 47 his section reviews ultrasound use in
the diagnosis and management of congenital musculoskeletal
abnormalities, including foot deformities, teratologic hip, congenital
limb deformities, congenital nonhip dislocations, and
brachial plexus injury. It also describes sonographic indings in
other conditions such inlammation and trauma speciic to
children. Tumors and sports injuries are discussed in other
musculoskeletal ultrasound chapters (see Chapters 23 and 24).
Nondevelopmental Dysplasia
Hip Abnormalities
Painful Hip and Hip Joint Effusion
A variety of conditions cause hip pain in pediatric patients,
including transient synovitis, osteomyelitis, Perthes disease,
slipped capital femoral epiphysis, fracture, and arthritis. Although
radiography is performed initially and is oten diagnostic, the
plain radiographic ilm oten is normal in the presence of small
joint efusions. Sonography can be used to determine if an efusion
is present and to guide arthrocentesis. Several large studies of
sonographic hip joint efusion detection have been reported.
hey show the technique to be easy to master and rapidly
performed. he results have been highly sensitive in the detection
of efusion, with as little as 1 mm of luid recognized experimentally.
False-negative results have been reported in infants
younger than 1 year, 48 probably because the femoral neck has
not developed and the capsule is small. Fluid tends to surround
the femoral head instead.
Although hip sonography is sensitive in the detection of
efusion, its place in the workup of the painful hip varies from
center to center. In one large series, although ultrasound facilitated
early diagnosis or prompted further investigation in some patients,
it altered the therapy or outcomes in only 1% of the patients. 49
Clinicians use a number of physical signs (oral temperature,
weight bearing) and laboratory indings (white blood cell count,
C-reactive protein, erythrocyte sedimentation rate) to distinguish
septic arthritis from transient synovitis in children. 47,50,51 hey
employ these parameters when making the decision to perform
joint aspiration or seek additional imaging.
At our institution, the workup of the painful hip is individualized,
and we ind hip sonography to be helpful in certain circumstances.
When the clinical picture is unclear, the presence
or absence of an efusion can guide the clinician in the diagnosis
and the need for further evaluation. For example, in the patient
with clinical and laboratory signs of transient synovitis, hip
sonography may be used to demonstrate an efusion; however,
the patient does not usually undergo joint aspiration. In a patient
with hip pain and signs of sepsis, MRI may be performed,
regardless of the results of hip ultrasound, to exclude osteomyelitis
and other sot tissue infection sites. MRI provides a more detailed
evaluation of localized disease beyond the hip joint.
he patient is examined in the supine position with the hips
in the neutral position with as little lexion as possible. A highfrequency
linear transducer is recommended. he hip is scanned
in a sagittal, oblique plane along the long axis of the femoral
neck (Fig. 55.5). he brightly echogenic anterior cortex of the
femoral head and neck with the intervening echolucent physis
is seen; the anterior margin of the bony acetabulum is visualized
superiorly. he anterior recess of the joint capsule parallels the
femoral neck in this area, with the outer margin forming an
echogenic line anterior to the cortex of the femoral neck and
extending over the femoral head. he iliopsoas muscle is supericial
to the capsule.
In the normal hip, the joint capsule has a concave contour
and the thickness of the capsule from the outer margin to the
cortex of the femoral neck measures 2 to 5 mm. When there is
joint efusion, the anterior recess of the capsule becomes distended
with a convex outer margin, and luid is seen between the anterior
and posterior layers of the capsule. 52 here is increased thickness
of the abnormal joint capsule of at least 2 mm compared with
the normal contralateral capsule. 53-55 he use of measurements
alone is problematic when both hips are abnormal, although
this occurs infrequently.