Case History: A 30 years old
was referred for evaluation of swelling in right
forearm following a
trauma.
Findings: The study was
done on GE VOLUSON 730PRO color Doppler with
10 MHz high frequency linear probe. Gray
scale sonogram showed a large thick
walled complex pulsatile cystic mass with mobile internal echoes adjacent to right ulnar
artery ( Fig 1). Color Doppler image of the same lesion showed color flow
signals within it with swirling pattern, suggestive of a vascular mass,
probably pseudoaneurysm. An eccentric area of focal aliasing noted near ulnar
artery through which blood is seen gushing in and out, s/o neck of pseudoaneurysm which is arising from the right
ulnar artery proximal to wrist (Fig 2).
Turbulent flow was well demonstrated in pseudoaneurysm with the classic "ying-yang"
appearance on color flow imaging (Fig 2, 3). Spectral Doppler sampling from the pseudoaneurysm neck showed the
characteristic to-and-fro blood flow pattern( Fig 4).
Diagnosis: Post traumatic
pseudoaneurysm of right ulnar artery.
Discussion: A pseudoaneurysm,
or false aneurysm is a confined collection of thrombus and blood associated
with disruption of one or more layers of an artery wall (1). Pseudoaneurysm is
a typical complication of arterial puncture performed for diagnostic angiography
or interventional procedures and is observed in up to 4% of persons after
percutaneous transluminal angioplasty (PTA) and cardiac catheterization (Hust and
Schuler 1992; Moll et al. 1991). A suture aneurysm is a
pseudoaneurysm
developing after vascular surgery, in particular
after
bypass operations.Less commonly, pseudoaneurysm can result from rupture of a
native vessel or leakage at the site of a surgical anastamosis. Common femoral
artery pseudoaneurysms complicating catheterization procedures are by far the
most common. However, pseudoaneurysms can occur anywhere. Patients with
pseudoaneurysms usually present with a mass in the
area of
trauma that may be pulsatile ,as seen in this case.
Pseudoaneurysms differ from true aneurysms in
that the latter contain all three histologic layers of the arterial wall,
whereas pseudoaneurysms contain less than three and often none of these layers
and contained by only compressed fibrous tissue. The pseudoaneuyrsm lumen is
connected to the underlying artery by a cylindrical neck-variable in length and
diameter.
An
aneurysm is seen on gray-scale images as a saccular or spindle-shaped
dilatation of the vessel lumen.
The
definitive diagnosis of pseudoaneurysm requires detection of the neck
connecting
the pseudoaneurysm with the injured artery, and identification
within
this neck of the pathognomonic``to and fro'' spectral waveform pattern (Fig-4) [3].
To-and-fro flow occurs in the neck of a pseudoaneurysm due to changing
pressures: at the high intraluminal pressure during systole, blood flows
through the narrow neck into the aneurysm at a rather high velocity. Under the
reversed pressure conditions during diastole, the blood flows back into the
artery at a slightly lower flow rate. Reflux is typically turbulent ( Fig 2).
Ultrasound
is the imaging modality of choice to differentiate between pseudoaneurysm and
non-communicating hematoma.
A false
aneurysm must be differentiated from a perivascular hematoma with transmitted
pulsation, but this is difficult on clinical grounds (Thomas et al. 1989).
Using duplex ultrasound,an aneurysm can be differentiated from hypoechoic,
perivascular
structures such as lymphnode, hematoma, seroma, or lymphocele by the depiction
of to-and-fro flow, which is diagnostic of a pseudoaneurysm and requires
no angiographic confirmation.
Arteriovenous
(A-V) fistulas may coexist with pseudoaneurysms. Grayscale sonography rarely
reveals any detectable abnormalities in patients with isolated A-V fistulas. In
many patients high-velocity flow at the site of an A-V communications results
in turbulence and focal perivascular tissue vibration. This can produce a
dramatic color-Doppler display of random red and blue pixels in the
perivascular soft tissues. Another hemodynamic consequence of an A-V fistula is
decreased resistance to flow in the artery supplying the fistula. Direct
arterial inflow into the vein produces turbulent flow in the venous lumen and
often produces an arterialized venous waveform or a turbulent waveform.
The objective
of doppler imaging is to differentiate between hematomas associated with pseudoaneurysm
and those that are not. Whereas hematomas resolve spontaneously, a
pseudoaneurysm can potentially rupture and therefore must be identified,
closely monitored and in most instances, treated.
Before
ultrasound enabled the precise localization of the aneurysmal neck relative to
the skin surface, the treatment of choice was surgical closure. With advances
in ultrasound equipment, it is now possible to occlude over 90% aneurysms by compression
of the neck using color duplex imaging for guidance (Fellmeth et al. 1991;
Hust et al. 1993). Thrombosis occurs after 10–30 min of compression.Success
rates of 70–90% have been reported for ultrasound guided compression of
pseudoaneurysm (Krumme et al. 1995; Lange et al. 2001) compared with 95–100%
for induction of thrombosis by sonographically guided thrombin injection into the
aneurysmal sac (Vicente and Kazmers 1999; Wixon et al. 2000).
So to conclude color Doppler US is
cost effective and reliable imaging modality to diagnose pseudoaneurysms,
and can also be utilized for guided compression and thrombin therapy.
Fig 1- Gray scale imaging showing complex cystic pulsatile mass in forearm along ulnar artery
.
Fig-2
Color doppler imaging showing color aliasing at the neck of pseudoaneurysm due to
turbulent blood flow.
Fig 3-
Color flow imaging showing characteristic “yin-yang” sign due to swirling
pattern of blood flow. The red and blue color flow signals due to inflow and
outflow turn of blood respectively via neck of pseudoaneurysm.
Fig 4-
Duplex spectral waveform sampling in the ulnar artery pseudoaneurysm neck
demonstrating characteristic
to-and-fro blood flow.
Contributed by: Dr. Subhash Tailor, Dr. Gopal Dhakar, Radiologists, Bhilwara,
India.
Address for correspondence:-Dr.Gopal Dhakar,14 Ramsnehi hospital campus,
Bhilwara. Email-gld444@gmail.com.
References: .1. William J. Zwiebel, John S. Pellerito. Introduction to vascular
ultrasound, 5th edition (2005), Elsevier Saunders, P 391-392.
2. Carroll BA, Graif M, Orron DE. Vascular ultrasound. In: Kim DS,
Orron DE, eds. Peripheral Vascular Imaging and Intervention.
St.Louis: Mosby Yearbook, 1992: 211±25.
3.Abu-Yousef MM, Wiese JA, Shamma AR. The ``to-and-fro'' gn:
Duplex Doppler evidence of femoral artery pseudo-neurysm. AJR
1988;150:632
