M & M (Mediastinal Mass) – When rare is really rare!

Clinical History

A 65-year-old man presented to the emergency department with dyspnoea and chest pain.
The patient had a previous history of coronary artery bypass grafting (CABG) 16 years before, hypertension, hyperlipidaemia under pharmacological control, and 20 pack years of active smoking.
General physical examination was unremarkable.

Imaging Findings

Chest radiograph showed cardiomegaly and a rounded left perihilar mass with loss of silhouette sign with the left heart border. Previous sternotomy is noted (Fig. 1).
Computed tomography (CT) of the thorax presented a low-density mass on the left side of middle compartment of the mediastinum measuring 6 x 7 cm (Fig. 2). This lesion extended from the level of the aortic arch to the left atrium (Fig. 3).
Post iodinated contrast administration, the lesion showed enhancement of a central zone within a peripheral low-density and non-enhancing area, in keeping with a vascular lesion with parietal thrombus (Fig. 5).
Extensive calcification of the native coronary arteries is seen (Fig. 3) with coronary bypass grafts extending from the aorta and the anterior descending coronary artery, right coronary artery (Fig. 3) and left circumflex coronary artery (Fig. 4).
The mass compressed the main and left pulmonary arteries (Fig. 5).

Discussion

In the reported case the differential diagnosis of the lesion includes a wide range of entities such as lymphadenopathy aortic arch aneurysm, enlarged pulmonary artery, fore-gut duplications cysts (bronchogenic, oesophageal, neuroenteric), pericardial cysts, and tracheal lesions [1, 2, 3].
On contrast-enhanced CT the lesion was shown to be connected directly with an ascending aorta side branch and continuing with the left circumflex coronary artery. Taking in account the history of a previous 16-year CABG, this lesion is consistent with an aneurysm of a saphenous vein graft.
Saphenous vein graft aneurysm (SVGA) is an uncommon complication of CABG and can be asymptomatic or manifest as cardiac ischaemic events like chest pain or worsening dyspnoea due to graft thrombosis or distal embolism [4-8].
This type of aneurysms can be categorised as true aneurysms and pseudo- or false aneurysms. The major distinction is that true aneurysms occur in 10-20 years after surgery [4, 6, 7] and are usually fusiform, while pseudoaneurysms occur early in the post-operative period, are located near anastomotic sites between the graft and the native artery and are typically saccular in shape [4, 5, 6].
This distinction is important because while true aneurysms will require surgery [4, 8], pseudoaneurysms may be successfully treated with minimally invasive procedures such as covered stent placement or coil embolisation.
The aetiology of true and false SVGA is unclear, but risk factors for its development include post-operative infection, tight suture anastomoses, suture dehiscence, trauma to the vessel during harvest, intrinsic weakness in venous walls at branching points or valve attachment, grafting of varicose veins, steroid therapy, as well as the typical atherosclerotic disease risk factors, such as hyperlipidaemia, smoking and hypertension [4, 6, 7, 8].
In the reported case, the giant aneurysm has a fusiform shape, comprises the mid-portion of the vessel, and presents approximately sixteen years after CABG in a man with clear risk factors for atherosclerosis. This is the pattern of a true aneurysm of a saphenous vein graft.

Differential Diagnosis List

Final Diagnosis

Saphenous vein graft aneurysm after coronary artery bypass grafting.

URL:	https://www.eurorad.org/case/12479
DOI:	10.1594/EURORAD/CASE.12479
ISSN:	1563-4086