Diagnostic ultrasound ( PDFDrive )

1612 PART V Pediatric Sonography
FIG. 47.18 Elevated Pulsatility of the MCA in 12-Year-Old With
Headaches. TCD image of the right MCA demonstrates an elevated
RI of 0.76. Normal RI values should range from 0.43 to 0.58 after fontanelle
closure.
should have normal pulsatility; thus an elevated RI in cases where
ventricular size is increased may imply the need for a shunt. Hill
and Volpe 126 irst described a decrease in diastolic/systolic low
in 11 hydrocephalic infants. Because it is noninvasive and repeatable,
Doppler sonography has been increasingly used to assess
changes in cerebral hemodynamics in hydrocephalus through
the anterior fontanelle in infants. It can be used through the
temporal bone in older children as well. 4,127,128 here is a direct
correlation between the ICP (from experimental fontanometric
and direct measurement evidence) and the RI. he increasing
RI is predominantly caused by a reduction in the EDV. 128,129 he
vascular indices most oten applied in hydrocephalic patients
are RI and PI. Both ratios minimize the error in estimating true
velocity caused by a varying angle of insonation. his is particularly
important in hydrocephalus because vascular anatomy can
be distorted by ventricular enlargement, and a small angle of
insonation cannot be assumed. 130 Diiculties with using the RI
to determine hydrocephalus have occurred because (1) there is
a wide range of normal RI values (0.65-0.85 in the neonate,
0.60-0.70 in the child before fontanelle closure, and 0.50-0.60
in older children and adults through temporal window ater
fontanelle closure), 14 and (2) many other intracranial and
extracranial factors can change the RI other than increased ICP 131
(Table 47.4). herefore the RI must be correlated closely with
the clinical condition of the patient.
TABLE 47.4 Factors That Change Cerebral Doppler Indices
Resistive Index
Systolic Velocity
INTRACRANIAL ABNORMALITIES
Intracranial bleed Increased Beat-to-beat variation, risk factor for IVH
Periventricular leukomalacia
Increased
Asphyxia
Decreased initially
Brain edema
Increased
Hydrocephalus
Increased, reverses after drainage
Subdural
Increased
Brain death Increased Decreased, reversed diastolic low
ECMO
Decreased
Vascular malformations Decreased Increased, turbulence
EXTRACRANIAL ABNORMALITIES
PCO 2
Inverse relationship
Heart rate
Inverse relationship
Shock
Decreased systolic/diastolic
Patent ductus arteriosus
Increased
Pneumothorax
Increased
Cardiac ischemia
Increased
Gastrointestinal bleed
Increased
Polycythemia, hyperviscosity Increased Decreased
Anemia
Increased
DRUGS
Indomethacin Increased Decreased
Maternal cocaine
Increased
Exogenous surfactant
Increased
ECMO, Extracorporeal membrane oxygenation; IVH, intraventricular hemorrhage; PCO 2 , carbon dioxide partial pressure (tension).