Diagnostic ultrasound ( PDFDrive )

CHAPTER 47 Doppler Sonography of the Brain in Children 1607
Left ACA
A
B
FIG. 47.14 Anterior Cerebral Artery (ACA) Stenosis in 11-Year-Old Child With Sickle Cell Disease. (A) TCD sonogram demonstrates
abnormally elevated left ACA velocities. (B) Three-dimensional time-of-light MR angiogram demonstrates stenosis at the origin of the A1 segment
of the left ACA (arrow).
When assigning the risk of stroke based on TCD velocities,
it is important to consider how velocities may difer with the
overall health of the patient, patient ethnicity, and the speciic
equipment used compared to those obtained with nonduplex
equipment in the initial STOP studies. When ill, comorbidities
including hypoxia, fever, hypoglycemia, and worsening anemia
can increase the cerebral blood low velocities, making the results
invalid if conditional or abnormal. 56 In these cases, repeating
the study when the patient is no longer ill will help verify the
results. Because diferent ethnicities and haplotypes of the disease
have diferent average velocities, risk of stroke, and prognosis,
it is possible that diferent criteria have to be determined to
assess risk for a speciic ethnicity. 87
Regarding the equipment used, studies have evaluated the
diferences in nonimaging TCD versus imaging TCD techniques.
In studies performed in the early 2000s, nonangle-corrected
velocities obtained with Acuson and ATL TCDI equipment were
approximately 10% lower in the MCA than those obtained with
Nicolet (Vascular, Madison, WI) nonimaging equipment. 20,21
Later studies showed no signiicant diference in TAMM velocity
measurements obtained with General Electric TCDI equipment
compared with Nicolet nonimaging equipment. 22,23 he reasons
for these difering results are likely multifactorial. Early imaging
probes were bulkier, making it more diicult to optimize Doppler
tracings. Padayachee et al. 88 discussed how the TAMM velocity
is quantiied using the Doppler equation. Optimizing the waveform
without angle correction can result in similar results
compared to the nonimaging TCD technique negating the need
for decreasing the threshold for TCDI cutofs. 88 A 10% lower
cutof point for TAMM velocities has been suggested depending
on the protocol and machine used. 13 Besides appropriate curser
placement, instrument settings (volume size, gain, waveform
display) should be optimized. Close attention to technique can
reduce the diferences between velocity data acquired with
diferent ultrasound machines. Centers should be aware of these
potential diferences and perform their own comparison studies
when using various imaging equipment before changing velocity
thresholds for TCDI. 88
Although angle correction with TCDI may be a way to
correct for lower velocities obtained by TCDI compared with
nonimaging TCD, this technique has not yet been validated and
may overestimate stroke risk in children with SCD. 25 herefore
angle correction currently is not recommended when performing
and interpreting TCDI for stroke risk assessment in pediatric
SCD. 12,13
he natural history of TCD velocities in sickle cell patients
continues to be studied. 89-91 he STOP 2 trail was performed
to assess when discontinuation of transfusion therapy was
appropriate. Ater 30 months of transfusion treatment and
normalization of TCD velocities, patients were randomized to
continue or suspend transfusion therapy. STOP 2 demonstrated
that patients in whom transfusion therapy was suspended ater
normalization of TCD have a return to abnormal TCD velocities
with a higher occurrence of stroke, and are more likely to develop
silent clinical infarcts, indicating the need to continue transfusion
treatment. 92,93
Optimal management for children with abnormal velocities
remains problematic, with no consensus regarding long-term
therapy in children with persistently abnormal velocities. he
side efects of prolonged transfusion therapy have clinicians
searching for other methods of improving stroke risk, including
the use of hydroxycarbamide (hydroxyurea) therapy and bone
marrow transplant. 62,94-96 Hydroxyurea with phlebotomy proved
to be useful in the prevention of stroke recurrence during the
SWiTCH protocol, but not as good as transfusion therapy with
chelation. 97,98 Other studies (TWiTCH trial) are evaluating the
use of hydroxyurea in the prevention of primary stroke in patients
with abnormal TCD velocities.