Hidden in Plain Sight: Unmasking a Pseudoaneurysm Without Contrast.

Pseudoaneurysms are the outpouching of arterial walls confined to one or two layers, unlike true aneurysms which affect all three arterial wall layers (the intima, media, and adventitia). If peripheral, like in the femoral artery, ultrasound can be used for its diagnosis, but particularly in cases of large pseudoaneurysms of the aorta, an accurate characterization with CT angiography is recommended for treatment planning. In patients who cannot undergo an injection of contrast medium, as with our patient who was affected by severe renal insufficiency and had incidental evidence of an inhomogeneous lesion nearby the descending thoracic aorta at CT, the use of MR represents a valid alternative to diagnose the pseudoaneurysm. Indeed, by applying proper protocol using T2w True Fast Imaging with Steady-State Free Precession (TRUFI) and T1 Dixon sequences, we have been able to accurately characterize the pseudoaneurysm, ruling out other vascular findings such as intramural hematoma, or mediastinal lesions, such as undifferentiated pleomorphic sarcoma. This case highlights the value of MR without contrast for vascular assessment.