Age / Sex : 57 / F

 C.C.: right lower leg weakness and pelvic pain for 8 months

chronic contained rupture of isolated internal iliac artery aneurysm simulating neurogenic tumor

Discussion

Findings:
1. Axial contrast-enhanced computed tomography (CT) of the sacrum obtained with the intradural injection of contrast material shows a sacral mass and widening of the right sacral foramen with continuity along the posterior margin of the Internal iliac artery(IIA). CT 2 cm lower shows an atherosclerotic plaque anterior to the IIA and contrast material clearly extravasating into a pseudoaneurysm.
2. Magnetic resonance imaging (MRI) of the sacrum show a presacral mass with peripheral high signal intensity and central low signal intensity on T1- and T2-weighted images. The sacral canal is completely eroded by what appears to be a presacral mass. Extravasating cavity showing strong enhancement of the anterior half portion of the mass containing an unenhanced chronic thrombus on contrast-enhanced T1-weighted MRI. Differential Diagnosis: Neurogenic tumor

Diagnosis: Chronic-Contained Rupture of an Isolated Internal Iliac Artery Aneurysm simulating neurogenic tumor

Discussion:
The causes of an IIA aneurysm are atherosclerosis, infection, trauma, and disorders of the arterial wall. Progressive atherosclerosis is thought to be the most common cause[1]. Iliac arterial aneurysms usually develop in connection with aneurysms of the abdominal aorta, which have an incidence of approximately 10%, while isolated iliac aneurysms are rare and occur in only 2%[2]. An isolated IIA aneurysm is even more unusual, with an incidence of 0.4%[3]. The mechanism of chronic-contained abdominal aortic aneurysm rupture is not fully understood. It is believed that in case of large aneurysms, as the sac increases in size, it causes a strong perianeurysmal reaction, which subsequently protects against the extravasation of blood if the aneurysm ruptures[4].

References:
1. Dix FP, Titi M, Al-Khaffaf H. The isolated internal iliac artery aneurysm--a review. Eur J Vasc Endovasc Surg 2005;30(2):119-29.
2. Richardson JW, Greenfield LJ. Natural history and management of iliac aneurysms. J Vasc Surg 1988;8(2):165-71.
3. Short DW. Aneurysms of the internal iliac artery. Br J Surg 1966;53(1):17-20.
4. Sterpetti AV, Blair EA, Schultz RD, Feldhaus RJ, Cisternino S, Chasan P. Sealed rupture of abdominal aortic aneurysms. J Vasc Surg 1990;11(3):430-5.