Page 111 - Libro 2

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Intracranial Cerebrovascular Examination
Colleen Douville
OBJECTIVES
Describe the arterial segments of the intracranial cerebral circulation that are standard to examine with transcranial Doppler (TCD) and transcranial duplex imaging (TCDI) techniques
Describe the anatomical approaches used to insonate the intracranial vessels in adults
List the current clinical applications for transcranial Doppler examinations
Describe normal velocities for each intracranial arterial segment examined with TCD and TCDI
Define the diagnostic criteria used to make the interpretation of collateral flow
List the values used for interpretation of 􏰀50% stenosis of the middle cerebral and intracranial internal carotid arteries
List criteria for vasospasm of the middle cerebral artery
Define the use of extracranial to intracranial ratios in vasospasm
KEY TERMS
anterior cerebral artery | anterior communicating artery | basilar artery | collateral flow | intracranial stenosis | middle cerebral artery | posterior cerebral artery | posterior communicating artery | transcranial Doppler | transcranial duplex imaging | vasospasm | vertebral artery
GLOSSARY
circle of Willis a roughly circular anastomosis of arteries located at the base of the brain
collateral a vessel that parallels another vessel; a vessel that is important to maintain blood flow around another stenotic or occluded vessel
Lindegaard ratio middle cerebral artery (MCA) mean velocity divided by the submandibular internal carotid artery (ICA) mean velocity;
this ratio is useful in differentiating increased volume flow from decreased diameter when high velocities are encountered in the MCA or intracranial ICA
pulsatility expressed as Gosling’s pulsatility index (peak systolic velocity minus end-diastolic velocity divided by the time averaged peak velocity)
Sviri ratio ratio calculation used to determine va- sospasm from hyperdynamic flow in the posterior circulation; the bilateral vertebral artery velocities taken at the atlas loop are added together and averaged; this averaged velocity is then divided into the highest basilar mean velocity
transcranial Doppler (TCD) a noninvasive test that uses ultrasound to measure the velocity of blood flow through the intracranial cerebral vessels
transcranial duplex imaging (TCDI) a noninva- sive test on the intracranial cerebral blood vessels that uses ultrasound and provides both an image of the blood vessels as well as a graphical display of the velocities within the vessels
vasospasm a sudden constriction in a blood vessel causing a restriction in blood flow
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