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In search of biological and radiological markers of aneurysm instability
12/4/13

Aneuvrysm 80mm“But not all large aneurysms rupture, while small ones sometimes do”, stresses Natzi Sakalihasan. “What’s more, in older patients, surgery can sometimes do more harm than good.” Taking these arguments into account, Professor Sakalihasan has spent the past 25 years or more studying the definition of criteria that would allow us to define abnormal growth and, above all, assess the risk of rupture. “We are endeavouring to find the means to identify potentially dangerous aneurysms”, specifies the professor. To this end, he is working in close collaboration with GIGA’s Laboratory of Connective Tissues Biology (LBTC) at the University of Liège, led by Professor Alain Colige and the Department of Nuclear Medicine led by Professor Roland  Hustinx.

Connective tissues constitute the majority of our body mass and are particularly involved in supporting, protecting and feeding organs. They are made up of cells dispersed in a network of molecules forming fibres, such as elastin and collagen, thus creating an extracellular “matrix”. “Big blood vessels, such as the aorta, are essentially comprised of two layers of connective tissue of a different composition. This setup is responsible for the mechanical resistance and elasticity of the arterial walls, two fundamental properties allowing them to adapt to the stresses and deformations associated with the blood flowing through the vessels each time the heart beats", points out Professor Colige.

An efficient but  expensive scanner

During previous studies, Natzi Sakalihasan and Alain Colige’s teams examined, among other things, the proteins in the extracellular matrix of the aortic walls: elastin and collagen, which are responsible respectively for elasticity and the mechanical resistance of connective tissue. “In simple terms, we could say that the deterioration of the elastin causes the appearance of the aneurysm and that its rupture is generally associated with the destruction of the collagen”, summarises Natzi Sakalihasan. The researchers have already shown a correlation between the instability of an aneurysm and the presence of MMP-9 and -2, enzymes that participate in the deterioration of elastin and collagens. 

Another study carried out in 2002 by the teams at Liège’s CHU and CHC, revealed that recourse to the PET-CT (positron emission tomography - computed tomography) medical imaging method was efficient in detecting aneurysms that are likely to rupture. “This type of scanner uses a radioactive marked glucose analogue as a tracer to spot areas of high metabolic activity, such as inflamed tissue”, explains Natzi Sakalihasan. “Since abdominal aortic aneurysms can be considered as a chronic inflammatory disease, we thought of using a PET-CT scan to examine patients”, he points out.  The researchers were thus able to observe that aneurysms with a high metabolic activity ran a greater risk of rupture. This method could thus allow doctors to decide whether surgery is necessary, regardless of the size of the aneurysm. But this solution isn’t accessible to everyone: “Not all hospitals are equipped with a PET-CT and the examination is quite expensive”, Natzi Sakalihasan reminds us.

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