Non-traumatic aortic arch pseudoaneurysm: CT findings

Clinical History

A 79-year-old man presented with dyspnoea and weakness in the lower limbs. Medical history was characterised by congestive heart failure and atrial fibrillation. Two months earlier he was admitted to the hospital for a pleural, pericardial and perihepatic effusion. The patient reported neither recent nor past traumas.

Imaging Findings

Chest X-ray showed the presence of a right opacification and a pleuric effusion (Fig. 1); an HRCT was performed. It described collaterally a mediastinal mass that displaced the bottom of the right pulmonary artery and compressed the tracheal carina and oesophagus (Fig. 2). An acute/subacute vascular lesion or a neoplasia were suspected so a contrast-enhanced CT was performed: the mass in the aortic-pulmonary window presented an early, progressive enhancement in arterial, venous, and late phase and the walls were thickened (Fig. 3-4). In the early arterial phase a jet of enhancement starting from the aortic lower wall to the pseudoaneurysm could be seen. In the same phase another thin jet of lower enhanced blood from the pseudoaneurysm towards the aortic lumen was noted, a retrograde flow compared to the previous one (Fig. 5).The jet originated from a small interruption of the aortic wall in the context of a parietal atheromatous calcification.

Discussion

Aneurysms are focal dilatation of blood vessels; they can be divided in true aneurysms, in which the wall is formed by all the three aortic wall layers, and false aneurysms where the wall has fewer than three layers and they are usually contained by adventitia or periadventitial tissues [1]. Thoracic aortic aneurysms are usually caused by atherosclerosis (70%); pseudoaneurysms (false aneurysms) are more often saccular with a narrow neck and are usually due to trauma, penetrating atherosclerotic ulcers or infection (mycotic aneurysms). Post-traumatic aneurysms are linked to blunt trauma, very often may result from a rapid deceleration: the distal part of the thoracic descending aorta moves in an inertial way compared to the proximal part that is held back by intercostal vessels and ligamentum arteriosum [2]. Another mechanism is the “osseous pinch” where the thoracic aorta is compressed between the spine posteriorly and the manubrium, first rib and medial clavicle anteriorly. A pseudoaneurysm may originate from a penetrating aortic ulcer which is characterised by a denudation of aortic intima with a progressing lesion that may affect a variable amount of the arterial wall. The aortic ulcer is associated with atherosclerotic changes, and an overlying thrombus might be found [3].
Aortic pseudoaneurysm is characterised by: acute angles between cranial end and caudal end of the focal bulge and the aortic wall, a dissection flap, and haemomediastinum [4]. Pseudoaneurysm is part of the differential diagnosis together with the ductus diverticulum, a convex focal bulge along the anterior lower surface of the isthmic region of the aortic arch [5]. Ductus diverticulum is reported to be a remnant of the closed ductus arteriosus, but it has been suggested that it may be a remnant of the right dorsal aortic root [6]. Compared to the pseudoaneurysm the ductus diverticulum has smooth margins with gently sloping symmetric shoulders and forms obtuse angles with the aortic wall.
The forward and backward jet indicates bidirectional flow due to swirling of blood within the sac.
The flow through the hole in the vessel wall between the vessel and the pseudoaneurysm lumen is responsible of this previous finding and another sign called "yin-yang sign", common to (true or false) aneurysm [8].
The treatment must be sudden in order to improve the patient’s survival chances. Surgical repair remains the standard of care for correcting aortic pseudoaneurysm, but importantly endovascular repair with occluders, stent grafts or coils is an option for high-risk surgical patients [7]. Our patient died before the treatment.

Differential Diagnosis List

Final Diagnosis

Spontaneous aortic arch pseudoaneurysm-related penetrating atherosclerotic ulcers

URL:	https://www.eurorad.org/case/15543
DOI:	10.1594/EURORAD/CASE.15543
ISSN:	1563-4086