Prediction of Hemorrhagic Stroke

Predicting Hemorrhagic Stroke
Predicting Hemorrhagic Stroke - Snapshots of simulations performed by Nagargoje and colleagues

Clinicians can assess whether a patient's brain aneurysm is at risk of rupture with the help of patient-specific modeling.

The circulatory system is shaped by blood as it circulates throughout the body. Understanding how blood flow affects arteries and veins is critical to diagnosing and treating disorders such as aneurysms, which are bulges that can develop in blood vessels. The function of blood flow in rupture of a rare type of aneurysm has now been studied experimentally and statistically by a group of neurosurgeons and engineers. The findings can be used to identify risk factors in people struggling with the disease.

Aneurysms can occur when the wall of a blood artery weakens. Although the majority of brain aneurysms are benign, if one ruptures, the patient may experience a hemorrhagic stroke, a medical emergency with a greater than 50% chance of death. The size of an aneurysm often determines whether it should be treated surgically; The minimum diameter for treatment is normally 7mm. However, aneurysms with dimensions below this limit can still cause strokes.

Thanks to advances in medical imaging, it is now possible to capture in-vivo 3D images of a brain aneurysm. Clinicians and scientists can use these images to statistically solve equations that describe how blood moves through the aneurysm and its attached vessels.

According to the scientists, these solutions can be used to predict the risk of an aneurysm bursting.

Theoretically and empirically, scientists have determined that ruptured aneurysms are more likely to have a noticeable balloon-like shape before they burst, but such predictions have yet to be made in a clinical setting. But the nature of an aneurysm, the patterns of blood flow within it, and how the risk of rupture interacted was still unclear.

Mahesh Nagargoje of the Sree Chitra Tirunal Institute of Medical Sciences and Technology in India, along with colleagues, investigated three patients with internal carotid artery bifurcation aneurysms, a rare and potentially dangerous condition.

An aneurysm that develops between two arterial branches is difficult to operate without damaging the brain and nearby blood vessels.

The team used digital subtraction angiography to photograph each aneurysm and Doppler ultrasound to determine the blood velocity in the associated vessels. Using this information, they created a model of the blood flow through the neck, dome, and outlet of the aneurysm.

The team discovered that the friction between the blood and the vessel wall causes a high shear stress in the neck walls for the aneurysm with the smallest neck width-to-dome radius ratio and a low shear stress on the dome walls, where the model shows that the blood is stagnant.

Previous research has linked both these features with aneurysms that carry a significant risk of rupture. Blood hits the aneurysm walls in areas of high shear stress, and researchers believe this may facilitate the growth of the aneurysm. White blood cells can adhere to the inside of the aneurysm due to the low shear stress, and researchers believe this could lead to an immunological response that weakens the artery walls.

For the most complex patterned aneurysm, scientists discovered irregular blood flow in the first chamber and stagnation in the second chamber; The second aneurysm had grown from the first, causing a number-eight bulge.

The research team suggests that the clinical finding that irregularly shaped aneurysms are more prone to rupture may be explained by stresses on the first chamber walls and weakening of the second chamber walls.

Although the study is still in its infancy, Jayanand Sudhir, who worked with Nagargoje, says he and his colleagues believe they are "on the right track" in identifying variables that affect the likelihood of rupture.

Predicting Aneurysm Rupture

Makoto Ohta, a medical engineer at Tohoku University in Japan, has a personal interest in using computational fluid dynamics models to predict aneurysm rupture, but believes that much more extensive research is needed before researchers can draw firm conclusions.

Italian fluid mechanics expert Lorenzo Botti adds a similar cautionary note in interpreting these findings. Population studies are necessary to support any theory of how hemodynamics affects pathology.

According to Sudhir, the team plans to collect information on at least 200 more aneurysms. Sudhir believes that if their initial results are correct, clinicians could start using their model to recognize and treat high-risk aneurysms, which could lower the death rate.

Source: physics.aps.org/articles/v15/s153

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