Our patient was a 50-year-old woman who underwent thoracoabdominal CT for endometrial cancer staging. Her only relevant medical history was an appendectomy, and she was otherwise asymptomatic.
Two-phase multi-detector computed tomography (CT) was performed.
Unenhanced CT showed a well-defined rounded left anterior mediastinal mass with the same density of vascular structures (45 HU) (fig. 1). The mass had well-defined boundaries and measured 35 x 28 x 48 mm (L x T x AP).
Contrast-enhanced CT showed a saccular mass filled homogeneously with contrast material and a communication with the left brachiocephalic vein (fig. 2). There were no signs of intraluminal thrombus.
The diagnosis of left brachiocephalic vein pseudoaneurysm was made.
Venous pseudoaneurysm of superior mediastinum are rare clinical entities. Brachiocephalic vein pseudoaneurysm are even rarer, with only 37 cases reported worldwide. The pathophysiology is still not well understood but some possible etiologies include congenital malformations, inflammation and degenerative changes in the vessel’s wall, trauma or endovascular manipulation. There is also an association with hemangioma, hygroma and neurofibromatosis type 1. [1, 2]
Most of the diagnosed cases are incidental findings since they usually are asymptomatic, as happened in our case. [3, 4, 5] However, it can sometimes course with cough, dyspnea, chest pain or hoarseness due to compression of the recurrent laryngeal nerve. [1, 6, 7] As with any venous pseudoaneurysm, serious conditions like compression of bordering structures, thromboembolism, venous obstruction and rupture may develop. 
The most common finding of a venous pseudoaneurysm or aneurysm of the brachiocephalic trunk is a widening of the mediastinum in routine radiographs (not available). [1, 4, 6] A contrast-enhanced CT should be performed to clarify the cause of the widening. CT can give us the diagnosis when showing a well-defined mass with a venous connection with the brachiocephalic trunk. We can also rule out the presence of thrombus, when the enhancement of the mass is homogeneous.[5, 7, 8] Contrast stasis within the pseudoaneurysm may be present as higher density within the lesion when compared to adjacent vessels, as shown in image 2. Taking into account that our case had a pedicle originating from the left brachiocephalic vein, a diagnosis of pseudoaneurysm was assumed. Venography, echocardiography, MR imaging or duplex ultrasound can also be useful to diagnose and characterise these lesions. Sometimes, exploratory thoracoscopy is necessary to settle the diagnosis. 
It is difficult to establish treatment guidelines since thoracic venous pseudoaneurysms are not common clinical entities, and there are some different ways to manage them. They can be managed conservatively with only follow-up, with anticoagulation and anti-aggregation or with surgical resection if the aneurysm is symptomatic, enlarging or disfiguring. [5, 6, 9] In our case, even with a large pseudoaneurysm, conservative treatment was chosen since the patient didn’t have any symptoms or risk factors needing anticoagulation treatment.
Although rare, it is important to consider venous pseudoaneurysm as the cause of mediastinal enlargement and as differential diagnosis of anterior mediastinal mass. The correct diagnosis and management are crucial to avoid complications which can be fatal.
Written informed patient consent for publication has been obtained.
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