Teaching Case

An 81-year-old male patient, with previous uneventful history of arterial line for endovascular thrombectomy of stroke 1.5 months before, presented with pain and progressive swelling on the inner right elbow.

Colour Doppler evaluation was performed and revealed a large vascular structure with communication to the humeral artery, presenting a typical yin yang sign and a “to and fro” flow pattern, confirming a 5 x 3.5 cm humeral artery pseudoaneurysm (Fig. 1, 2). The pseudoaneurysm was surgically removed.

While true aneurysms involve all three layers of the arterial wall (intima, media and adventitia) and the risk of rupture is proportional to the size of the aneurysm, pseudoaneurysms arise from disruption of only one or more layers, thus are more prone to rupture, regardless of size. [1, 2]. Humeral pseudoaneurysms are rare and are usually iatrogenic (arterial catheterisation or puncture) or associated with trauma [3].

Clinically, they can be asymptomatic or present as a painful pulsatile mass when superficial, and can complicate with thrombosis, rupture, limb ischaemia or compression of nervous or venous structures [3].

Colour Doppler is a noninvasive diagnostic technique and should be used in the initial evaluation [1]. Pseudoaneurysm manifests as a cystic vascular structure adjacent to an artery, communicating with it through a neck. At the level of the neck, a “to and fro” waveform represents the blood entering and leaving the aneurismal sac, during systole and diastole, respectively [1]. The yin yang sign results from turbulent swirling motion of blood inside a true or false aneurysm, indicating a bidirectional flow (Fig. 3) [2]. Additionally, a haematoma may be seen within the pseudoaneurysm.

Treatment options include ultrasound-guided compression, surgical repair or minimally invasive endovascular treatments (embolisation, stent-graft placement, ultrasound-guided thrombin injections) [1, 2].

Teaching points

The main causes for humeral pseudoaneurysms are trauma and invasive medical procedures.

Colour Doppler is indicated for initial evaluation and diagnostic of pseudoaneurysms.

The yin yang sign represents the turbulent bidirectional flow within an aneurysmal sac.

Written informed patient consent for publication has been obtained.