Clinical History
An 80-year-old man with a history of aortic aneurysm was admitted for abdominal pain. A CT angiography was performed demonstrating an abdominal aortic aneurysm, with signs of impending rupture (Fig. 1, 2). An endovascular treatment was programmed.
However, the patient presented acute hypotension while waiting for the endoprothesis.
Another CT angiography demonstrated signs of acute intraperitoneal bleeding.
Imaging Findings
The first CT image showed an infrarenal aortic aneurysm (11.7x11.6) with signs of contained rupture: hyperdensity of the thrombus, loss of identification of the posterior wall that closely follows the anterior contour of the vertebral body and discontinuity in circumferencial wall calcifications.
The second CT demonstrated an active extravasation of contrast material from an anteroinferior defect in the aortic wall of the infrarenal aortic aneurysm. Contiguous to the aneurysm, an acute retroperitoneal haematoma was depicted that extended anteriorly to the left anterior pararenal fascia with displacement of adjacent structures.
Discussion
Abdominal aortic aneurysm (AAA) is a pathological dilatation of the abdominal aorta more than 3 cm in the greatest diameter [1].
The average age of diagnosis is 65-70-years and it is more common in men. Atherosclerosis is one of the strongest risk factors along with genetic and environmental factors.
Aneurysms may develop in any segment of the aorta, but the most often involved is the segment below the renal arteries because of lower concentration of elastin and vasa vasorum, making this segment more vulnerable to aneurysm formation [1, 2].
AAA rupture is the most important diagnosis to exclude in patients with abdominal pain specially when it is associated with back or flank pain.
The clinical triad of aneurysm rupture includes abdominal pain, pulsatile abdominal mass and shock [2, 3].
Risk factors for AAA rupture include female gender (two to four times increased risk), large initial aneurysm diameter, low forced expiratory volume in one second (FEV1), current smoking history, elevated mean blood pressure and a history of cardiac or renal transplantation [4].
CT-angiography is the gold standard method for studying aneurysms, including the complicated ones. CT findings that indicate impending rupture are: increased aneurysm size, hyperattenuating crescent sign, draped aorta, and focal discontinuity of intimal calcification or tangencial calcium sign (the calcium is pointing out away from the expected circumference of the aneuryms).
The hyperattenuating crescent sign refers to a periluminal curvilinear area of hyperattenuation within the wall or thrombus of the aorta. It represents an internal dissection of blood into the peripheral thrombus and it is one of the earliest and most specific imaging manifestations of the rupture process [3]. The draped aorta is an area in which the posterior aortic wall may not be identified as a distinct line. The posterior aorta follows the contour of the vertebral body (Fig. 1).
The primary signs of rupture are periaortic stranding, retroperitoneal haematoma, and active extravasation of intravenous contrast media that is demonstrated on contrast-enhanced CT images (Fig. 2-4) [1-5].
Rupture most commonly involves the posterolateral aorta with haemorrhage into the retroperitoneum (Fig. 2, 3).
After frank rupture, periaortic blood may extend to the perirenal space, pararenal space or the psoas muscles. Intraperitoneal extent may be an immediate or a delayed finding.
Identification of impending rupture is crucial because these patients are at risk for frank rupture and may benefit from a preoperative assessment, followed by urgent surgery [3]. When the surgical risk is high (eldery or underlying pathology) stent graft repair is recommended.
Differential Diagnosis List
Abdominal aneurysm rupture
Abdominal aneurysm rupture
Arterial disection
Mycotic aneurysm
Final Diagnosis
Abdominal aneurysm rupture
