Diagnostic ultrasound ( PDFDrive )

1512 PART V Pediatric Sonography
Neonatal sonography of the brain is an essential part of
newborn care, particularly in high-risk and unstable premature
infants. 1,2 Current ultrasound technology allows for rapid
evaluation of infants in the intensive care nursery with virtually
no risk. he advantages of sonography over computed tomography
(CT) or magnetic resonance imaging (MRI) include portability,
lower cost, speed, no ionizing radiation, no sedation, and real-time
visualization with video clips saved for later review. Screening
of premature infants for intracranial hemorrhage has proven
highly sensitive and speciic. Daneman and colleagues have
reported that optimal imaging of the neonatal brain requires
delineation of structures in both the near and far ields. hus
magniication of selected areas with focal zone and higher resolution
megahertz adjustments are essential for these detailed regional
assessments. 3,4 Real-time assessment is essential to detect subtle
changes in echogenicity of the brain parenchyma, especially
common in white matter injury of prematurity (WMIP). MRI
is very sensitive and speciic with regard to identiication of brain
injuries but, because of the cost and need for transfer of very
unstable premature infants, is typically performed at termequivalent
age if concerns regarding neurodevelopmental outcomes
are present.
Ultrasound is essential to the neonatal evaluation and follow-up
of hydrocephalus and periventricular leukomalacia (PVL).
Prenatal ultrasound and MRI diagnosis 5 of central nervous system
(CNS) malformations, infection, or masses is now followed up
by ultrasound in the neonatal period. When major anomalies
are present, associated anomalies may need evaluation by neonatal
MRI. CT is not indicated in premature infants because of the
lack of good gray versus white matter diferentiation from the
high water content in the newborn brain. 6 For the same reason,
CT is rarely used for term infants unless there is a history of
birth trauma.
Ultrasound can be useful for the follow-up of ventricular
shunt therapy or possible complications. Color and spectral
Doppler ultrasound of cranial blood low may prove valuable,
particularly for cystic lesions when the diferential diagnosis
includes a vascular lesion, or for possible subdural hematomas,
and to separate normal vascular structures from clot. Doppler
ultrasound is also useful in infants receiving extracorporeal
membrane oxygenation (ECMO) or when decreased blood low
is a risk for infarction (see Chapter 46).
EQUIPMENT
In the premature infant, a 7.5-MHz or higher transducer is
recommended to obtain the highest resolution possible. A 5-MHz
transducer may be necessary to allow for adequate sound penetration
of a larger infant head. 7 Electronic phased array transducers
with a 120-degree sector angle and multifocal zone capabilities
are generally used for imaging through the anterior fontanelle.
Small-footprint, linear array, high-frequency transducers (up
to 12 MHz) can provide high-quality images for scanning of
near-ield pathology through the anterior fontanelle. hese
transducers are best for subdural hematomas, meningitis, superior
sagittal sinus thrombosis, and cerebral edema, and in some cases,
migrational abnormalities, 8 or for scanning over the mastoid
fontanelle, posterior fontanelle, and foramen magnum. he
squamosal portion of the temporal bone is thin but may require
a 5-MHz transducer if not imaged through the mastoid fontanelle.
he multifocal zone capability provides excellent resolution
throughout the ield of view, but requires a cooperative patient
because the frame rate is slowed signiicantly. Compound
imaging, allowing for multiple angles of insonation, is also useful
when imaging through small spaces such as the fontanelles. Video
clip capabilities are invaluable in an uncooperative infant or
when documenting motion, such as blood low.
It has become routine to save video clips for later review,
to prevent repeating an examination if there is a questionable
inding and to be certain that each view has been completely
evaluated. Clips can greatly improve the understanding of the
pathology. Areas of increased or decreased echogenicity may
be extremely subtle on single images, but they become much
more apparent when integrated with cine or video that captures
real-time ultrasound indings and the relationship to normal
structures.
SONOGRAPHIC TECHNIQUE
Currently, most brain sonographic examinations are performed
through the anterior fontanelle in both the coronal and the
sagittal planes. It has become clear that the neonatal brain is not
fully examined unless the posterior fossa is evaluated through
the posterior and mastoid fontanelles. In fact, cerebellar hemorrhage
has been proven by MRI correlation to be missed without
the mastoid views of the posterior fossa. 9 Posterior fossa malformations
may not be well understood without these highly
detailed views of the cerebellum, fourth ventricle, and cisterna
magna. 10-12 hus the posterior fossa views from the mastoid
fontanelle are extremely important in the evaluation of cerebellar
hemorrhage or posterior fossa anomalies, which are quite
common. Good skin-to-transducer coupling can be achieved by
an acoustic coupling gel. Occasionally, a standof pad can be
useful to evaluate supericial abnormalities such as subdural
hemorrhage, but a higher resolution transducer is a better option
to evaluate the near ield in detail.
It is very important to use color Doppler ultrasound imaging
to evaluate luid collections because some cystic areas are actually
vessels. If extracerebral luid collections are expected, they are
better evaluated with CT or MRI. Axial ultrasound scanning
has been used extensively in utero, particularly for accurate
measurements of fetal ventricular dimensions. In the newborn,
axial scanning is used in evaluation of the posterior fossa through
the mastoid fontanelle and to evaluate the circle of Willis with
color Doppler ultrasound. 7,13-15 Doppler evaluation of the major
cerebral arteries may be indicated with particular attention to
the resistive index changes that can indicate cerebral blood low
abnormalities. Color and spectral Doppler may show hyperemia,
and they can be used to depict patency and low in the major
dural sinuses (see Chapter 46). he posterior scanning techniques
are the best approach to evaluate the occipital horns for ventricular
clot. he foramen magnum approach may be useful when
evaluating the upper spinal canal, as in patients with a Chiari
malformation.