Diagnostic ultrasound ( PDFDrive )

CHAPTER 50 The Pediatric Chest 1721
Thymus
showing starry
sky appearance
A
Thymus:
right lobe
Thymus:
left lobe
Aorta
SVC
SVC
Aorta
PUL
PDA
B
C
FIG. 50.31 Normal Thymus and Great Vessels of Chest. (A) and (B) Longitudinal and transverse sonograms show normal thymus echotexture
in a 31-month-old boy. Superior vena cava (SVC) and aorta are visible through the thymic window. (C) Gray-scale rendering of a color Doppler
image shows normal great vessels in the chest in transverse scan through the thymus in another child. PDA, Posterior descending artery; PUL,
pulmonary artery.
transversely from let to right, posterior to the thymus, to enter
the SVC. his is useful to determine catheter position (Fig. 50.32)
and the presence of a thrombus in children with central venous
catheters.
Doppler examination is useful in identifying thrombus within
the subclavian vein, SVC, and pulmonary artery (Fig. 50.33).
hrombosis of the axillary or subclavian vein secondary to thoracic
outlet syndrome 46 is seen on ultrasound Doppler study in Paget-
Schroetter syndrome 47 (Fig. 50.34). It results from an abnormal
insertion of the costoclavicular ligament laterally on the irst rib,
along with hypertrophy of the scalenus anticus muscle.
he Doppler waveform is abnormal when thrombosis or
obstruction of the SVC is present. Doppler ultrasound indings
include (1) loss of biphasic SVC waveform, (2) continuous forward
low rather than distinct systolic and diastolic peaks, (3) a turbulent
low proile, (4) increased velocity downstream, and (5)
decreased velocity upstream. 48 Venous thrombosis is reported
in 20% of children receiving extracorporeal membrane oxygenation
(ECMO). 49 Doppler waveforms may be diferent in patients
receiving ECMO because their resistive indices are low. Recurrent
SVC thrombosis has been reported in a child with activated
protein C resistance. 50
Superior Vena Cava Thrombosis: Doppler
Sonographic Findings
Loss of biphasic waveform
Continuous forward low (no systolic or diastolic peaks)
Turbulent low
Increased downstream velocity
Decreased upstream velocity