The floating aorta or CT angiogram sign

A 56-year-old man presented with severe chest pain in the emergency room and elevated D- dimmer levels. A CT pulmonary angiogram (CTPA) was requested in order to rule out pulmonary embolism.

CTPA showed a posterior mediastinal soft-tissue attenuating mass arising posterior to the aorta and displacing it anteriorly. The mass was expanding bilaterally reaching the parietal pleura of both lungs and its maximum dimensions on axial plane was 67x 68 mm. Despite the fact that the mass was encasing aorta and its branches, posterior intercostal arteries were patent with no sign of occlusion. There was also a thickening of the diaphragmatic pleura and dilatation of the bronchial arteries (Figure 1-2).

The CT of the pelvis that followed showed a similar mass measuring 10 x 93 x 10 mm (Transverse x Anteroposterior x Craniocaudal respectively). This mass caused obstruction of the left ureter, leading to its dilation (Figure 3).

Biopsy results of this tissue showed that it was a Diffuse large B cells lymphoma (non-Hodgkin lymphoma) stage IV according to the Cotswolds-modified Ann Arbor classification.

Aortic displacement from the vertebral column, known as floating aorta or CT angiogram sign, has been described as a CT sign of retroperitoneal masses [1]. The paraspinal mass may elevate the aorta and inferior vena cava off the spine without causing stenosis or invasion, a sign that is characteristic of lymphoma [2]. The normal abdominal aorta maintains a close relationship to the vertebral column. Any retroperitoneal mass arising posterior to the aorta can slide between the aorta and the vertebral column and displace the aorta anteriorly, and hence the term floating aorta or CT angiogram sign. The distance between the vertebral column and the aorta should not be more than 10 mm in men and 7.3 mm in women. [3]

Lymphoma, mediastinal cysts, and neurogenic neoplasms are the most common primary middle and posterior mediastinal tumours. Lymphoma may involve the anterior, middle and posterior mediastinum, as lymphadenopathy or as a discrete mass. [4] More specifically, non- Hodgkin lymphoma (NHL) frequently manifests in extranodal structures in the chest, often in the form of secondary involvement but occasionally as primary disease too. Radiologists should have a high degree of suspicion in patients at risk such as in immune-compromised patients with autoimmune diseases, a history of stem cell or solid organ transplant or with particular imaging appearances including the floating aorta or CT angiogram sign, the vertebral wraparound sign, non-resolving lung consolidation, an infiltrative soft-tissue mass, and lesions demonstrating vascular encasement without invasion. [5]

Spinal involvement in lymphoma may also appear as a wrapping paraspinal soft-tissue mass associated with extensive involvement of a vertebral body but with relatively sparing of the bony trabecula and cortex that could account for the absence of vertebral compression fractures and height loss, despite extensive bone marrow involvement.[2] This appearance has been termed the wraparound sign and is thought to represent extensive marrow disease infiltrating through the vertebral cortex into the paraspinal tissues with relatively little involvement of the structural bone.[6] It is a specific feature that allows the radiologist to make a relatively confident diagnosis of lymphoma. [6]

CONCLUSION

Some tumours grow and extend into spaces between pre-existing structures and surround vessels without compressing their lumina. Lymphomas, lymphangiomas and ganglioneuromas are examples of such tumours. The floating aorta or CT angiogram sign and the wraparound sign should raise our suspicion for such neoplasms, especially for NHL.