CT PROTOCOL
We used the following multidetector CT protocol:
o Non enhanced;
o Post-contrast acquisitions;
o Multiplanar reconstructions (axial, saggital, coronal, curved and MIP)
Out of the 156 studied cases, 62,9% presented with suspicion or diagnosis of abdominal aneurysm and aneurismal complications and 37,1% were incidental findings.
CT FINDINGS
1. Asses and measure Fig. 6 :
In most cases of complicated aortic aneurysms the vessel wall is covered by an intraluminal thrombus, which generally does not obstruct blood flow.
Fig. 6: Infrarenal fusiform aortic aneurysm with significat circumferential thrombosis (orange arrows) and severe wall calcifications (blue arrow).
2.Check aortic branches Fig. 7 / adjacent organs Fig. 8
Thrombosis can extend in the aortic branches and cause secondary organ impairement.
Fig. 7: Infrarenal fusiform aneurysm (blue arrow) with calcified aortic and iliac wall (green arrows) presents severe circumferential thrombosis (red arrow) that extends into the left common iliac artery with no contrast enhancement at this level (red arrow)
Fig. 8: Same case from Fig. 6 with narrowed and unenhanced left renal artery (red arrow) with a secundary scleratrophic kidney (blue arrow).
3.Worst case scenario Fig. 9
Although mural thrombosis frequently accompanies aneurysmal disease, complete thrombosis is a distinctly unusual complication that requires immediate surgical intervention.
Fig. 9: Infrarenal fusiform aneurysm with severe aortic wall calcifications (green arrow) with contrast enhancement at the level at of the mesenteric artery (red arrow) and complete aneurysmal thrombosis (blue arrow) starting inferior to the renal arteries
1. Understand and asses
There is a two way street between dissection and aneurysm, an aneurysm can cause a dissection and a dissection can cause an aneurysm because of the thin elastic tissue laminae.
Aortic dissections are part of the acute aortic syndrome and imply an intimal tear which allows blood to penetrate into the medial layer producing two lumens (false and true) separated by an intimo-medial flap. 1, 2 Fig. 10
Fig. 10: Aortic dissection
Stanford classification
· Type A: affects ascending aorta and arch;
· Type B: begins beyond brachiocephalic vessels;
An aortic dissection tends to spiral around the aortic axis and branching vessels can be involved in the process Fig. 11 .
Fig. 11: Fusiform ascending aorta aneurysm with spiraling Stanford type A dissection: blue arrows: B- aortic cross, C- aorta at celiac trunk (emerging from false lumen), D- aorta at the superior mesentery artery (emerging from true lumen), E – aorta at the left renal artery level (emerging from false lumen); and branches: yellow arrows A – dissection involving both common carotid arteries; F- dissection involving common iliac arteries. The false lumen is marked with black star.
2. How many dissection flaps?
Because the intimo-medial flap is very thin and moves rapidly with the pulsating blood flow it can create the false double contour appearance 3 (in reality there is only one flap) – motion artifact. Fig. 12
Fig. 12: Descending aortic aneurysm with dissection that has a false double contour because of the heart pulsations. The double contour aspect changes aspect in later scan phases
In severe cases there can be a secondary dissection in the wall of the false lumen. It is also called the Mercedes Benz sign. Fig. 13
Fig. 13: Aneurysm of the ascending aorta and dissection with two flaps also named the “Mercedes benz” sign - the two flaps maintain the same aspect in all scan phases
3. How to differentiate the true lumen from the false lumen?.
The false lumen 3:
· has a larger lumen size;
· is partially thrombosed, more common in chronic dissections Fig. 14;
Fig. 14: Aortic dissection with thrombosed false lumen
· associates the beak sign = acute angle formed at the edge of the false lumen in axial cross-section; Fig. 15
Fig. 15: Dissection of the descending aorta showing the "beak sign"
· is of lower contrast value in the early scans and higher density value in the late scans; Fig. 16
Fig. 16: Lower contrast value of the fals lumen in an ECT examination of aortic dissection
· can present the cobweb sign = strands of media crossing the false lumen and appearing as thin filiform filling defects; Fig. 17
Fig. 17: Aortic dissection with false lumen presenting cobwebb sign
- Penetrating atherosclerotic ulcer (PAU)
An aortic ulcer is generated by the erosion of an atheromatous plaque disrupting the internal elastic lamina. 1,2 Fig. 18
Fig. 18: Penetrating atherosclerotic ulcer
The thinned out aortic wall caused by the aortic aneurysm can aggravate the progression of PAU, therefore increasing the risc of progression towards dissection, pseudoaneurysm or rupture. 2 Fig. 19
Fig. 19: Partially thrombosed infrarenal saccular aneurysm that associates multiple penetrating atherosclerotic ulcers (orange arrows) one of which has progressed towards a pseudoaneurysm (blue arrows)
The most important complication of aortic aneurysms is represented by rupture. The larger the diameter of the aneurysm, the greater is the likelihood of rupture. 2,3 Fig. 20 , Fig. 21
Fig. 20: Infrarenal fusiform aortic aneurysm (blue cross) and severe aortic wall calcifications that associates a periaortic dense accumulation (density ~37-40 UH) that increases after contrast administration (red arrow) – aspect suggestive of possible fibrotic tissue
Fig. 21: Infrarenal saccular aortic aneurysm (blue cross) that associates multiple periaortic and iliopsoic subacute hematomas (red arrows) with a density of ~31-46 UH – blood in different stages of degradation.
Mass effect on adjacent organs and structures
The larger the size of the aortic aneurysm, the more adjacent structures it affects. Fig. 22 , Fig. 23 , Fig. 24
Fig. 22: Infrarenal fusiform aortic aneurysm that associates multiple old hemorrhagic accumulations (red crosses) with mass effect on the superior mesenteric and left renal artery (blue arrow), pancreas and duodenum (green arrows).
Fig. 23: Infrarenal fusiform aortic aneurysm (blue arrows), with kinking above the dilatation and severe aortic wall calcifications, that has mass effect on the right ureter (yellow arrow) causing grade II hydronephrosis on the ipsilateral kidney (yellow arrow)
Fig. 24: Infrarenal fusiform aortic aneurysm with periaortic and iliopsoic hemorrhagic accumulations that have mass effect on the lumbar vertebras with scalloping into the vertebral anterior slope (blue arrows).
STRUCTURED REPORT
When writing a structured CT report regarding an aortic aneurysm the following aspects are to be considered :
Location and number of aneurysms;
Shape
Dimensions (longitudinal/ AP and axial diameter);
Patent luminal diameter and thrombus thickness;
Characteristics of the wall:
- Calcifications
- Thrombosis
- Ulceration (s)
- Hematoma
- Dissection
- Soft atheromatous plaques (stable/unstable)
Aortic size above and below the aneurysm;
Complications:
- Thrombosis (partial/total)
- Fissure with active bleeding
- Inflammation
- Mass effect
Signs of impending rupture;
Relationship to involved branches/structures;
Anatomical variants
Incidentalomas