Diagnostic ultrasound ( PDFDrive )

CHAPTER 12 The Retroperitoneum 459
Thrombosis
he iliac veins and IVC are large veins with high-volume low.
hey are less prone to primary thrombosis than are deep veins
of the extremities. Perhaps the most common scenario to result
in IVC thrombosis is when clot embolizes into an IVC ilter.
Isolated iliac vein thrombosis is uncommon, occurring in 1.6%
of cases of lower extremity deep venous thrombosis. 133
Iliac thrombus most oten results from extension of lower
extremity venous thrombosis. Extrinsic compression of the IVC
or iliac veins, as in May-hurner physiology or a gravid uterus,
may also result in thrombosis. Iliac vein thrombosis in adults is
infrequently directly seen sonographically because of lack of an
adequate window. Most oten, the possibility of iliac thrombosis
can only be inferred sonographically.
Sonographic clues to iliac vein thrombosis are found in the
common femoral veins. When thrombus in the common femoral
vein extends as far proximally as can be seen, it is easy to infer
possible extension into the iliac veins. More subtle cases involve
continuous, low, or absent low in an open (nonthrombosed)
common femoral vein. Common femoral vein waveforms generally
show respiratory phasicity or cardiac phasicity, or both. When
phasicity is not clearly seen, as in continuous, low, or absent
low, it suggests obstruction to low more proximally (Fig. 12.32).
Before ordering other tests to look for more proximal obstruction,
it is worthwhile to perform a few maneuvers to eliminate
nonpathologic causes of lack of phasicity. First, have the patient
remove underwear if it is tight. Second, sonographically check
the fullness of the bladder. If moderately or greatly distended,
the patient should be asked to empty the bladder. hird, if the
patient is in the second or third trimester of pregnancy, check
the waveforms in posterior oblique or decubitus positions. If
the compression is caused by the gravid uterus compressing the
veins, these maneuvers will oten allow the waveform to return
to normal, showing that there is no ixed blockage of the veins
(Fig. 12.33).
A
B
C
FIG. 12.32 Venous Duplex Doppler Ultrasound
for Left Leg Swelling. (A) Waveform
in the left femoral vein lacks phasicity. All veins
in the left thigh had similar waveforms. There
was no thrombus found anywhere in the left
leg. The examination was mistakenly read as
normal. (B) Normal waveform in the right
common iliac vein. (C) Left leg was reexamined
the next day and now shows extensive thrombus.
When the irst exam was performed, there was
likely iliac vein thrombus, which then had
extended into the common femoral vein 24 hours
later. Waveforms in the legs are often the only
sonographic clue of iliac vein thrombosis.