Diagnostic ultrasound ( PDFDrive )

972 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
A
B
FIG. 27.12 Popliteal Artery Aneurysms. (A) Popliteal artery aneurysm measures 1.2 cm diameter (arrows). (B) In a different patient, a 3.7-cm
popliteal artery aneurysm contains low-level echoes and is partially thrombosed (cursors).
the popliteal regions. 23 Less commonly, aneurysms are present
in the SFA. In more than half of patients with popliteal artery
aneurysm, they are bilateral. An association exists between
popliteal artery aneurysms and abdominal aortic aneurysm, and
thus if a popliteal artery aneurysm is found, the abdominal aorta
should be evaluated. here is also an association among peripheral
artery aneurysm, tobacco use, and hypertension. Peripheral artery
aneurysms may contain clot, which may result in distal emboli
with or without sot tissue ischemia and infarction. In these
cases, intervention is necessary regardless of aneurysm size. he
walls of an aneurysm may calcify, and the presence of calciications
may have some protective efects against rupture.
On gray-scale ultrasound, an aneurysm may appear as a
fusiform anechoic or hypoechoic mass along the course of an
artery. he Doppler signal depends on the amount of thrombus,
the size of the neck of the aneurysm, and presence of calciication.
Aneurysms may be saccular and commonly occur at branch
points. he normal popliteal artery measures 4 to 6 mm in
diameter. 24 A bulge or focal enlargement of 20% of the vessel
diameter constitutes a simple functional deinition of an aneurysm
(Fig. 27.12). Empirically, a 2-cm cutof has been used to determine
need for intervention. 25 For popliteal artery aneurysm, surgical
exclusion (ligation of the aneurysm) is the traditional treatment
and has high rates of success. 26 However, a recent meta-analysis
showed that endovascular repair has similar success. 27 Doppler
ultrasound can be used to monitor the success of the intervention.
28 Aneurysm exclusion with covered stents is an increasingly
used therapy in place of surgical intervention. Doppler ultrasound
can be used to monitor the patency of the stent and conirm the
exclusion of the aneurysm from the circulation. 29,30
Pseudoaneurysm
Pseudoaneurysm describes disruption of an artery with low
in a space beyond the vessel wall. It may arise from any arterial
structure and may occur with direct trauma or tumor or inlammatory
erosion. Pseudoaneurysms are found in less than 1% of
diagnostic angiography examinations and more commonly in
coronary angiography. 31 Pathologically, the arterial wall has been
at least partially breached. Outer arterial layers, perivascular
tissues, clot, or reactive ibrosis contain the pseudoaneurysm
sac. 32 he mechanism of pseudoaneurysm formation has been
well characterized. A hematoma forms adjacent to the artery
at the point of injury. Eventual lysis of the clot results in
pseudoaneurysm.
A pseudoaneurysm is diferent from an aneurysm in that at
least one layer of wall is disrupted. It difers from active extravasation
in that blood within the pseudoaneurysm lows back into
the feeding artery through a narrowed opening rather than into
adjacent tissues. Arteriovenous communication, when present,
is used to guide appropriate therapy. In patients with arteriovenous
communication, thrombin repair is contraindicated owing to
the potential for embolization of the thrombin into the venous
system with resultant unintended regions of thrombosis.
Gray-scale ultrasound is typically performed irst to identify
the abnormality. he pseudoaneurysm can appear as a round
or oval anechoic structure with or without associated thrombus.
When present, thrombus appears isoechoic or hypoechoic; it
may be located along the edge of the pseudoaneurysm lumen.
Attention should be directed to these areas of extraluminal
hematoma or any anechoic collections to determine if there are
areas of low with color Doppler. If low is detected, spectral
Doppler is next performed to characterize arterial versus venous
low and to exclude a superimposed AVF. In the patent portion
of a pseudoaneurysm, there may be turbulent or disorganized
intraaneurysmal low with a “yin-yang” appearance. Communication
of the sac with the adjacent artery occurs through a neck
with a typical “to-and-fro” biphasic low on spectral Doppler 33
(Fig. 27.13, Video 27.4). Measurement of the neck length and
diameter of the neck of the artery is performed as part of the
assessment before thrombin injection. A neck with larger diameter
has clinical implications because these are less successfully treated
by thrombin injection. If the sac is thrombosed, the neck may
represent the only patent portion of the pseudoaneurysm. At
least one-third of pseudoaneurysm require repair, but spontaneous
closure is common for pseudoaneurysm smaller than 1.8 cm in
diameter. 34 If the sac is patent, ultrasound-guided thrombin