Diagnostic ultrasound ( PDFDrive )

CHAPTER 27 Peripheral Vessels 979
A
B
FIG. 27.19 Subclavian Steal Phenomenon. (A) Reversed low in the right vertebral artery. Note that artery and vein are the same color, indicating
abnormal low direction in one of the vessels. (B) Magnetic resonance imaging conirms signiicant stenosis in the subclavian artery just distal to
the vertebral artery (arrow). See also Video 27.9.
FIG. 27.20 Subclavian Steal With Transient Flow Reversal in the
Vertebral Artery.
include evaluation for thrombus, localization for venous access
procedures, preoperative venous mapping for hemodialysis
AVF and grat placement, and postoperative hemodialysis AVF
and grat assessment. Key aspects of venous Doppler imaging
include knowledge of anatomy, scanning technique, and attention
to detail.
he most common indication for venous Doppler ultrasound
is to identify deep venous thrombosis (DVT). Undiagnosed and
untreated DVT can result in fatal pulmonary embolism (PE).
Sudden death is the irst symptom in about 25% of people who
have PE 64 (Fig. 27.23). Clinical evaluation of the peripheral venous
system is frequently diicult, nonspeciic, and oten inaccurate.
Clinical decision rules to improve pretest probability are recommended
by the American College of Physicians and the American
Academy of Family Physicians. 65-67 he Wells criteria generate
a score for certain physical examination indings and pertinent
clinical history. 68 Clinical factors associated with increased
probability of DVT include active cancer, immobilization, localized
tenderness along the distribution of the deep venous system,
swollen extremity, pitting edema localized to the symptomatic
extremity, collateral supericial veins, and previously documented
DVT.
A modiication of the Wells score creates two groups: DVT
unlikely or DVT likely. 69 Current guidelines recommend a
D-dimer test for those with low risk. 70,71 he D-dimer test
measures a degradation product of ibrin and has a high negative
predictive value that is sensitive, but not speciic for DVT. 72 If
the D-dimer test result is positive, the patient should be evaluated
with venous Doppler. As with patients without cancer, the
combination of low probability and negative D-dimer result can
exclude DVT in cancer patients. 73,74 In practice, many patients
do not undergo this workup. 75 Going directly to sonography is
frequently faster than waiting for workup results and may ofer
an alternative musculoskeletal diagnosis such as popliteal fossa
cyst. Also, in cases of technically limited sonographic evaluation
of the more central deep venous system (iliac veins and inferior
vena cava [IVC]), magnetic resonance venography or CT
venography may be more sensitive. 76
Sonographic Examination Technique
he supericial location of the upper and lower venous system
allows the use of linear, higher frequency transducers. he highest
frequency linear transducer that still gives adequate penetration
should be used to optimize spatial resolution. Typically the
examination is best performed using a 5- to 10-MHz linear array
transducer, with application of the higher frequency range in
upper arm, forearm, calf, and more supericial veins. A curved
array or sector probe in the 3- to 5-MHz range may be necessary