Diagnostic ultrasound ( PDFDrive )

1622 PART V Pediatric Sonography
A
B
FIG. 47.27 Intraoperative Guidance for Resection of a Supracerebellar Arteriovenous Malformation With Residual Feeders Status After
Glue Embolization. (A) Angiogram demonstrates a residual supracerebellar vascular malformation. (B) Intraoperative TCD via craniotomy helped
identify the vascular nidus (cursor).
A study evaluating the neurodevelopmental outcome in infants
undergoing surgery for congenital heart defects indicates that
low cerebral blood low velocities on TCD obtained in the postoperative
period is a marker of suboptimal cerebral perfusion. 183
Future TCD studies may help to develop improved methods
of cerebral protection during repair of complex congenital
heart lesions. 182,184,185
TCD has also been used during diagnostic and therapeutic
neuroangiographic and surgical procedures. 185 Asymptomatic
microemboli have been shown to enter the cerebral circulation
in large numbers during “routine” carotid angiography as well
as pediatric scoliosis surgery. High rates of microemboli may be
related to the presence of right-to-let cardiac shunts. 186 Intraoperative
guidance using contrast agents and three-dimensional
TCD is being investigated to improve the demonstration of
vascular anatomy (Fig. 47.27).
Outside of surgery, neuromonitoring by TCD has also been
done in patients with traumatic brain injury, intracranial hemorrhage,
diabetic ketoacidosis, 187 and sepsis in the intensive care
unit. 188 By evaluating low velocity responses to spontaneous or
induced changes in cerebral perfusion pressure, TCD can help
modify treatment. 176
A study evaluating the cerebral blood low velocity in children
on extracorporeal membrane oxygenation (ECMO) demonstrated
that higher velocities suggested to be secondary to
hyperemia were identiied 2 to 6 days prior to recognizing cerebral
hemorrhage. Further studies might demonstrate usefulness of
TCD in the monitoring and management of patients on ECMO. 189
Transcranial Doppler and Tissue
Plasminogen Activator
Ultrasound enhances the activity of tissue plasminogen activator
(TPA). TCD sonography can identify residual blood low signals
around thrombi and, by delivering mechanical pressure waves,
expose more thrombus surface to circulating TPA. he CLOT-
BUST international multicenter trial 190 showed that ultrasound
can enhance the thrombolytic activity of a drug with clinical
recovery from stroke with recanalization 2 hours ater TPA bolus.
his was seen in 25% of patients treated with TPA and TCD
compared with 8% who received TPA alone (p = .02). he use
of contrast-enhanced ultrasound and TPA was recently evaluated
in animals and proved to be more efective than TPA with
nonenhanced ultrasound, contrast-enhanced ultrasound without
TPA, or ultrasound alone. 190 Current ongoing clinical trials include
phase II studies of 2-MHz TCD ultrasound with contrast agents
or microbubbles. 191,192 Future applications using contrast agents
may include evaluating perfusion of brain tumors ater chemotherapy
and radiation.
Functional Transcranial Doppler
he use of TCD in functional evaluation of the brain is a complementary
tool. It is useful in the measurement of the lateralization
during cognitive tasks. It is noninvasive, has excellent temporal
resolution, and is not afected by motion artifact. 193 Perfusion
can also be evaluated and has a signiicant correlation with
indings on functional MRI and positron emission tomography
studies. Functional TCD is considered a useful examination in
the elucidation of the hemispheric organization of cognitive,
motor, and sensory functions in adults and children. 102
Other Potential Uses
Patients with beta-thalassemia (minor) have an increased risk
of stroke and may beneit from transfusion and splenectomy as
treatment. Studies demonstrate an increase in mean arterial
velocities in patients compared to controls. 194
Using TCD alone thus far has not predicted stroke risk in
patients with thalassemia major. 195 More studies are needed