A pseudoaneurysm, or false aneurysm is a confined collection of thrombus and blood adjacent to an artery with disruption of one or more layers of it . Pseudoaneurysm differ from true aneurysm in that the latter contain all three histologic layers of the arterial wall, whereas pseudoaneurysm 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 native artery by a cylindrical neck-variable in length and diameter , & shows typical blood flow in it . Pseudoaneurysm can be a complication of arterial trauma ,including arterial puncture during a diagnostic angiography or interventional procedures. Both True & pseudo aneurysms forms pulsatile masses, as former is truly pulsatile ,& later can only feebly shares the pulsations of native artery .
Ultrasound with color Doppler is the imaging modality of choice for this diagnosis , & here we present a case of pseudoaneurysm of ulnar artery following trauma with classical findings on color Doppler sonography .
Contributed by: Dr. Subhash Tailor, Dr. Gopal Dhakar, Radiologists, Bhilwara [Rajasthan ], India.
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). On the basis H/O trauma , USG B-mode , color & spectral Doppler findings the diagnosis of Post traumatic pseudoaneurysm of right ulnar artery suggested , which was later confirmed by angiography .
Discussion & review of literature
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). 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). The characteristic appearance of pseudoaneurysm in triplex ultrasound (B-mode combined with color and pulsed Doppler spectral analysis) include the presence of a hematoma of variable echogenicity, which may represent separate episodes of bleeding and rebleeding, expansile pulsatility and detection of turbulent flow (``yin-yang'' appearance) within the mass(Fig-3).
A false aneurysm must be differentiated from a perivascular hematoma with transmitted pulsation, but this is difficult on clinical grounds 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.
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 guidance.
Thrombosis occurs after 10–30 min of compression with success rates of 70–90% have been reported for ultrasound guided compression of pseudoaneurysm in literature , compared with 95–100% for induction of thrombosis by sonographically guided thrombin injection into the aneurysmal sac .
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 with mobile internal echos in realtime
Fig-2 Color doppler imaging showing color signals within cyst & 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.