Table 2.

Differential diagnoses table for mycotic pseudoaneurysm.

	US	CT	MRI
Mycotic PSA	On grey scale US: often appears as a cystic or anechoic mass with adjacent edema or hematoma On color doppler US: Yin-Yang sign of swirling blood. On spectral doppler US: “To and Fro” sign suggesting blood entering PSA sac.	Peri-aortic fat stranding/ inflammatory changes. Wall thickening / aortitis Eccentric outpouching of the main artery. During arterial phase, contrast should opacify the PSA and the communicating tract to the main artery. During delayed phase, the PSA may demonstrate delayed retention of contrast within the sac.	The MRI appearance of PSA is similar to plain and contrast enhanced CT. The PSA opacifies during arterial phase. May show delayed retention of contrast. There are inflammatory changes around the PSA (i.e. edema and fat stranding).
Traumatic PSA	Similar findings as above	Similar findings as above however the wall thickening/aortitis and periaortic inflammatory changes are usually absent or less extensive. Similar findings as above ** clinical history is important to help differentiate between mycotic and traumatic PSA.	Similar findings as above however the wall thickening/aortitis and periaortic inflammatory changes are usually absent or less extensive.
True aneurysm	Bulbous or fusiform abnormal dilatation of the aorta/artery. Color doppler US will show flow unless the aneurysm is completely thrombosed / occluded	Bulbous or fusiform abnormal dilatation of the aorta/artery. Contains all 3 layers of the vessel wall. Has mass-effect and can compress adjacent structures if the aneurysm is large. Abnormally dilatated aorta/artery with no evidence of contrast extravasation. Will show contrast flow unless within the true lumen the aneurysm is completely thrombosed / occluded.	Abnormally dilatated aorta/artery with no evidence of contrast extravasation. The true lumen is opacified with contrast. There may be intraluminal thrombosis.
Ruptured aneurysm/PSA	Fluid or hematoma surrounding aneurysm / PSA (usually hypoechoic) No flow seen in the on color or doppler.	Hyperdense fluid surrounding injured / aneurysmal artery. There is often associated surrounding inflammatory changes / fat stranding. Contrast extravasation from injured artery. Delayed scans will show diffusion of contrast into surrounding hematoma or structures.	The MRI appearance of ruptured aneurysm/PSA is similar to plain and contrast enhanced CT. There is contrast extravasation during arterial phase and diffusion of contrast into surrounding structures on delayed images. On non-contrast images you will see fluid surrounding the ruptured aneurysm/PSA demonstrating complex/heterogenous signal which depends on the age of blood.
Thrombosed (completely) PSA	Gray scale; will show as soft tissue mas closely related to vascular structure. Doppler: No flow will be seen within the periarterial mass.	Periarterial mass with increased density (35 to 50 HU depending on chronicity). look for atherosclerotic disease of the adjacent vessel, this may help to raise suspicion of underlying arterial wall ulcer. Periarterial mass will not show contrast flow if it is completely thrombosed. look for atherosclerotic disease of the adjacent vessel, this may help to raise suspicion of underlying arterial wall ulcer.	This would appear as a perivascular mass with complex T1/T signal depending on the chronicity of the thrombus. No contrast flow would be seen in the mass. GRE sequences would be helpful as it may show susceptibility artefacts.

PSA = Pseudoaneurysm.