Diagnostic ultrasound ( PDFDrive )

1614 PART V Pediatric Sonography
with idiopathic normal pressure hydrocephalus, baseline TCD
velocities were higher than in controls and demonstrated a
signiicant decrease in those who reported clinical improvement
ater the tap.
Vascular Malformations
Intracranial Doppler imaging is useful for detecting vascular
malformations in the unstable neonate. 3,137 he vascular malformation
may be imaged with color or power Doppler ultrasound.
Spectral analysis of the involved vessels will show high velocity,
with low pressure and low pulsatility caused by increased diastolic
low. hese hemodynamic qualities result in higher-than-normal
mean and PSV, in conjunction with turbulence and lower-thannormal
RIs (Fig. 47.20). TCD sonography can assess arteriovenous
malformation (AVM) with a sensitivity of 87% to 95%, 126-133,137-140
particularly when contrast enhancement is used. 46 A study
performed in adults comparing intraoperative contrast-enhanced
TCD with angiography demonstrated that TCD is less sensitive
(detected only 91.3% of AVMs diagnosed by angiography),
underestimates the size of the AVM, and provides limited
information regarding blood supply and venous drainage. 141
Because MRI afords an even higher sensitivity than TCD in
screening, Doppler imaging is used more oten to quantitate the
hemodynamics of AVMs and to monitor the efects of surgical
or endoluminal interventions. 142 Ater surgical or embolization
treatment, the decrease in systolic velocity and increase in RI in
the feeding arteries can be followed. In a study performed by
Kaspera et al. 143 in patients ater surgical resection or embolization
of the AVM, an increase and normalization of PI was noted
before a decrease in velocity. No correlation was seen between
the degree of normalization of the parameters and the extent of
the embolization of the AVM.
TCD ultrasound has also been used to assess other vascular
anomalies, such as Sturge-Weber syndrome, dural arteriovenous
istulas, and carotid-cavernous istulas. 144-146 In a series of patients
with Sturge-Weber syndrome, decreased arterial low velocity
and increased PI was noted in the afected MCA, suggesting
chronic hypoperfusion of the tissue secondary to venous stasis
or cortical vessel hypoplasia due to cortical atrophy. 145 he fact
that these indings were present even before the onset of symptoms
suggests that venous stasis results in cortical injury. 147 A diferent
study demonstrated increased velocities on the afected side
during seizures and a fourfold to sixfold increase in low in the
contralateral side. 147 In cases of arteriovenous istulas, an increase
in low velocity is present in at least one cerebral vein or venous
sinus, which decreases ater embolization. A venous low velocity
of more than 50 cm/sec is considered abnormal and should be
further evaluated. 40 In patients with carotid cavernous istulas,
Doppler can be used for detection and to follow treatment.
Asphyxia
TCD sonography has been used in the evaluation of hypoxicischemic
brain injury. Mild asphyxia typically does not alter
cerebral hemodynamics. 148 Severe or prolonged asphyxia may
result in impairment of cerebral autoregulation, producing an
increase in diastolic blood low and a decrease in cerebrovascular
resistance. 2 Intracranial Doppler imaging in the neonate has been
particularly helpful in predicting signiicant hypoxic-ischemic
brain injury. 1,149-152 Archer et al. 151 found 100% sensitivity of a
low RI caused by increased diastolic low in the ACA and MCA
and an adverse neurologic outcome when performed within the
irst 48 hours of the insult in the neonate. Stark and Seibert 149
reported 10 in 13 neonates with an initially low RI who later
developed severe neurodevelopmental handicaps. he inding
of increased diastolic low can also be useful in evaluating the
older child ater head injury or cardiac arrest to predict signiicant
cerebral injury before computed tomography (CT) indings
become evident (Fig. 47.21).
Cerebral Edema and
Hyperventilation Therapy
Head trauma initiates several pathologic processes that may result
in signiicant changes in cerebral hemodynamics. Diagnosis of
these abnormalities can be crucial for the appropriate management
of such cases. Ater a signiicant cerebral hypoxic insult, vasodilation
may initially occur with a resultant increase in diastolic
low velocity and a reduced RI during this early hyperemic phase.
As ICP increases, however, the diastolic low velocity begins to
decrease, and the systolic peak velocity has a “spiky” appearance. 2
As cerebral edema develops, there is further loss of forward
diastolic low, and RI increases. 129 Sequential TCD readings ater
a cerebral insult have been helpful in evaluating the presence of
edema and the course of treatment 153 (Fig. 47.22).
Treatment for cerebral edema includes hyperventilation. An
inverse relationship exists between carbon dioxide partial pressure
(Pco 2 ) and the RI. he higher the Pco 2 , the greater the vasodilation,
the greater the diastolic low, and the lower the RI. When
the Pco 2 is reduced, vasoconstriction results, with decreased
diastolic low and increased RI. hus CO 2 reactivity can be
measured assessing the RI. he cerebral blood low increases
4% per mm Hg rise in Pco 2 . 1,26,129,152 he absence of change in
the RI as the patient’s ventilation is increased is described as an
absent “CO 2 reactivity test” and is a sign of severe brain injury. 154
Because of this, RI can be used to monitor hyperventilation
therapy in cerebral edema associated with head trauma. 2,155 As
hyperventilation decreases the Pco 2 , the RI should increase with
the concomitant vasoconstriction of cerebral vessels. he clinician
must take into account, however, that increasing cerebral edema
will also increase the RI. herefore this measurement should be
closely correlated with other clinical and laboratory indings.
For example, hyperventilation treatment in a patient who has
an increasing RI in the face of no change in ICP suggests that
the treatment is causing too much cerebral vasoconstriction. In
this scenario the patient may beneit from a decrease in the
hyperventilation.
Evaluation of Right-to-Left Shunt
Although transesophageal echocardiogram provides a direct
evaluation of the cardiac structures, TCD can also be used in
the evaluation of right-to-let shunts. 156-158 TCD provides visualization
of emboli through the cerebral circulation. Valsalva maneuver
can be performed noninvasively at the bedside without requiring
sedation. 29 he observation of 10 microbubbles of agitated saline