Post traumatic posterior tibial artery pseudoaneurysm with arteriovenous fistula

A 19-year-old male, with history of trauma by iron rod, presented with pain and swelling over the left leg for 1week duration. No history of fever. On examination, there was a swelling in the posterior aspect of left leg in the mid third with visible pulsations and palpalbe bruit.

On ultrasound, a well-defined anechoic lesion of size 4 x 3 x 3 cm (CC x AP x TR) was seen arising from left posterior tibial artery with a hyperechoic focus abutting it. The lesion showed swirling sign-on colour Doppler.

On CT lower limb angiogram, extra luminal contrast filled lesion measuring approximately 4.8 x 3.3 x 3 cm (CC x AP x TR) was seen in the middle 1/3rd of left leg in the posterior compartment with perilesional hematoma. No active contrast extravasation. The lesion was arising from the left Posterior tibial artery with a metallic foreign body abutting the neck.

Early filling of the venae comitantes accompanying the posterior tibial artery, proximal to the site of pseudoaneurysm, with early filling of left Popliteal and femoral veins was seen during arterial phase. But distal to the pseudo aneurysm, the venae comitantes showed no contrast opacification in arterial phase.

A pseudoaneurysm is defined as a deficiency in arterial wall, which leads to accumulation of blood in the adjacent extra-luminal region. Hence, arterial blood leaks out of the vessel lumen forming a sac surrounded by soft tissue and compressed thrombus[1].

Ultrasonography (US) has been widely used as a first non-invasive imaging modality for the investigation of vascular diseases[2]. In pseudoaneurysms, grayscale usually illustrates hypoechoic cystic structure nearby a supplying artery[3]. In addition to that, blood flow in a cystic structure distinguished by swirling motion pattern “yin-yang sign”. The cornerstone of pseudoaneurysm diagnosis is mainly based upon the appearance of the communicating neck between the arterial vessel and pseudo aneurysmal sac with “to-and-fro” waveform at duplex Doppler ultrasonography. The “to” represents the arterial blood going into the pseudo aneurysmal sac in systolic cycle, while “fro” illustrate blood exiting the sac in diastolic cycle[4].

Traumatic arteriovenous fistulas are usually caused by penetrating trauma, accounting for as many as 90 % of cases. Blunt trauma is rarely the cause and it is responsible for the other 10 % [5]. Diagnosis is often delayed in these cases and is usually dependent on imaging studies. Imaging features of AV fistula by colour Doppler ultrasound includes low- and high-resistance flow in the supplying artery, high-velocity arterialized waveform in the draining vein, and turbulent high-velocity flow spectrum at the junction of the artery and vein [6].

On CT angiography, pseudoaneurysms can mimic true aneurysms, however could be differentiated by irregular margin and surrounding hematoma[6].CT and MR angiography of arteriovenous fistula typically show early contrast filling in the vein during the arterial phase. Digital subtraction angiography (DSA) provides most accurate details of parent artery, site of origin of pseudoaneurysm any associated complication such as dissection or thrombosis, and associated findings such as arteriovenous fistula[7].

It is important to differentiate pseudoaneurysm from contrast extravasation. Extravasation appears as extraluminal contrast collection, mostly flame-shaped or irregular with increasing density from early to delayed phases.

DSA remains gold standard in diagnosis of pseudoaneurysm and treatment via embolization. Surgical treatment of pseudoaneurysm consists of excision of the aneurysmal sac and arterial reconstruction. It is imperative to always treat a diagnosed AV fistula, since the ensuing shunt could lead to a volume load in the heart and even progress to cardiac insufficiency[8]. Our case was treated surgically with good clinical outcome.