Diagnostic ultrasound ( PDFDrive )

1598 PART V Pediatric Sonography
INDICATIONS FOR TRANSCRANIAL
DOPPLER IMAGING
Indications for Transcranial Doppler in Adults
Detection and follow-up of stenosis or occlusion in major
intracranial arteries
Monitoring of thrombolytic therapy
Detection of cerebral vasculopathy and evaluation of
collateral intracranial low
Detection and monitoring vasospasm
Detection right-to-left shunts and/or circulating cerebral
microemboli
Assessment of cerebral vasomotor reactivity
Adjunct in evaluation of cerebral death
Intraoperative evaluation of embolization, thrombosis, and
hyper/hypoperfusion
Assessment of arteriovenous malformations and
intracranial aneurysms
Evaluation of positional vertigo or syncope
Additional Indications for Transcranial
Doppler in Children
Evaluation of stroke risk in sickle cell disease
Detection and monitoring vasospasm
Assessment of intracranial pressure and hydrocephalus
Assessment of hypoxic ischemic encephalopathy
Assessment of cerebral vasomotor reactivity
Adjunct in evaluation of cerebral death
Assessment of dural venous patency and arteriovenous
istula
Intraoperative monitoring
Sickle Cell Disease
Neurologic manifestations are common in SCD and include overt
infarction or stroke, silent cerebral infarcts, and hemorrhage (rare
in children, more oten seen secondary to aneurysm rupture in
adults). 53 Stroke results in neurologic deicits, and silent cerebral
infarcts can result in academic and behavioral diiculties and
increase the risk of having a future stroke. 54 Patients present
with vasculopathy involving the large intracranial arteries, most
frequently the distal internal carotid artery and proximal middle
and anterior cerebral arteries. he vasculopathy can progress
for months to years before symptoms develop and can result
in formation of numerous small collateral vessels, consistent
with moyamoya syndrome. his occlusive vasculopathy is
characterized by endothelial damage with intimal thickening,
muscular proliferation, and inlammatory changes with or
without in situ thrombosis. 53,55,56 Hemodynamic abnormalities
in sickle cell anemia (including hyperemia, hypervolemia, and
cerebral vascular dilation) play a role in the development of
neurologic injuries, especially in the pathogenesis of silent cerebral
infarcts. 54
he incidence of stroke varies depending on the origin of
the patient and haplotype of SCD; for example, the incidence
is 4.1% in Mediterranean patients, 6.7% in irst-generation
African patients living in France, and 10% in African Americans
younger than 20 years of age. 57 Silent cerebral infarcts
are the more common type of cerebral injury in patients with
SCD. hey are described as a 3 mm or larger lesion seen on
at least two T2-weighted magnetic resonance imaging (MRI)
sequences with no history or clinical evidence of focal neurologic
deicit. 56 Silent cerebral infarcts can be seen in patients
younger than 1 year of age with reported incidences of 13%
by 13.7 months, 27% in patients younger than 6 years and
37% in 14-year-olds. 54 First and recurrent strokes can be
prevented, but not completely suppressed, by transfusion
therapy in patients at risk. 19,58 With transfusion treatment
the anemia is partially corrected and cerebrovascular reserve
is improved, 59 resulting in a decrease in TCD velocities 60 and
a reduction in the risk of stroke to less than 1%, 61 although
patients may still develop new silent cerebral infarcts (18% at
1-year follow-up and 28% at 2-year follow-up). 54 Bone marrow
transplantation has proved curative in young patients with
symptomatic SCD and has led to stabilization of nervous system
vasculopathy. 62
TCD sonography has proved to be a safe, reliable, and costefective
screening method for children at risk of stroke. A sensitivity
of 90% and speciicity of 100% detecting arteriopathy ater
stroke when compared to angiography has been described. 63 No
signiicant association has been identiied between silent infarcts
and TCD velocities 54,64 or magnetic resonance angiography
(MRA). 54
Adams et al. irst showed the efectiveness of nonimaging
Doppler sonographic studies in screening for cerebrovascular
disease in patients with SCD. 19,30,31,65 Using the transtemporal
and suboccipital approach, Adams et al. screened 190 asymptomatic
SCD patients and found in clinical follow-up that a
TAMM velocity in the MCA of 170 cm/sec or greater indicated
a patient at risk for development of cerebrovascular accident
(CVA, stroke). 65
Using duplex Doppler imaging, MRA, and MRI, Seibert
et al. 66 described ive indicators of cerebrovascular disease in
patients with SCD: (1) maximum velocity in the OA of more
than 35 cm/sec (Fig. 47.5), (2) mean velocity in the MCA of
more than 170 cm/sec (Fig. 47.6), (3) RI in the OA less than
0.6 (Fig. 47.7), (4) velocity in the OA greater than that of the
ipsilateral MCA, and (5) maximum velocity in the PCA or the
vertebral or basilar arteries greater than maximum velocity in
the MCA. An 8-year follow-up of 27 neurologically symptomatic
and 90 asymptomatic sickle cell patients showed all ive
original TCD indicators of disease were still signiicant. 67 Four
additional factors were also signiicant: (1) turbulence, (2) PCA
or ACA visualized without seeing the MCA (Figs. 47.8, 47.9,
47.10), (3) any RI less than 0.3, and (4) maximum MCA velocity
greater than 200 cm/sec (Fig. 47.11). he sensitivity of Doppler
ultrasound as a predictor of stroke was 94% with a speciicity
of 51%.