Diagnostic ultrasound ( PDFDrive )

CHAPTER 47 Doppler Sonography of the Brain in Children 1621
range that has the most robust autoregulation, better neuroprotection
can be provided during a procedure. 177
Intraoperative TCD monitoring of the velocity in the MCA
during carotid endarterectomy is an accepted clinical application
in adults. 6 Intraoperative complications of carotid endarterectomy
relate mainly to ischemia during cross-clamping, hyperemic
phenomena, or embolization of atheromatous or gaseous materials.
Ater ischemia, hyperemia can occur and is characterized by a
sudden increase in low velocity. High-amplitude spikes seen on
TCD spectral waveform and associated with an audible chirping
sound are caused by solid or gaseous microemboli as small as
30 to 50 µm. 178 Ischemia during cross-clamping is a classic
complication occurring in up to 10% of patients; it is caused by
incompetent intracranial collateral circulation, mainly the anterior
and posterior communicating arteries and the leptomeningeal
vessels. TCD ultrasound can be used to assess the efect of
carotid cross-clamping on the MCA in both children and adults
(Fig. 47.26).
TCD monitoring during cardiopulmonary bypass for
cardiac surgery has also been studied. TCD sonography can
demonstrate emboli showers that occur during aortic cannulation,
cardiac manipulation, or other surgical maneuvers. 179-181
Doppler ultrasound has been used to monitor low patterns
during cardiopulmonary bypass with a decrease in mean velocity
with increasing hypothermia noted. 182 Profound hypothermic
circulatory arrest and profound hypothermia with continuous
low-low cardiopulmonary bypass are used to facilitate repair
of complex congenital heart lesions. Extended periods of
profound hypothermic arrest may impair cerebral function
and metabolism and produce ischemic brain injury. TCD has
enabled the noninvasive intraoperative monitoring of cerebral
perfusion when using either circulatory arrest or low-low bypass.
A
B
C
D
FIG. 47.26 Plexiform Neuroibroma. (A) Left internal carotid artery (arrow) is patent but surrounded by the plexiform neuroibroma on MRI.
(B) Compression of left carotid artery at arteriography shows cross-illing from right side into left ACA. (C) TCD spectral waveform at time of
compression also shows good illing of left ACA from right side (reverse low in the left ACA). (D) Good illing of left MCA.