Elsevier

Surgical Neurology

Volume 72, Issue 5, November 2009, Pages 444-450
Surgical Neurology

Aneurysm
Patient-specific hemodynamic analysis of small internal carotid artery-ophthalmic artery aneurysms

https://doi.org/10.1016/j.surneu.2008.12.013Get rights and content

Abstract

Background

Prophylactic treatment of unruptured small brain aneurysms is still controversial due to the low risk of rupture. Distinguishing which small aneurysms are at risk for rupture has become important for treatment. Previous studies have indicated a variety of hemodynamic properties that may influence aneurysm rupture. This study uses hemodynamic principles to evaluate these in the context of ruptured and unruptured small aneurysms in a single location.

Methods

Eight small internal carotid artery-ophthalmic artery (ICA-Oph) aneurysms (<10 mm) were selected from the University of California, Los Angeles, database. We analyzed rupture-related hemodynamic characteristics including flow patterns, wall shear stress (WSS), and flow impingement using previously developed patient-specific computational fluid dynamics software.

Results

Most ruptured aneurysms had complicated flow patterns in the aneurysm domes, but all of the unruptured cases showed a simple vortex. A reduction in flow velocity between the parent artery and the aneurysm sac was found in all the cases. Inside the aneurysms, the highest flow velocities were found either at the apex or neck. We also observed a trend of higher and more inhomogeneous WSS distribution within ruptured aneurysms (10.66 ± 5.99 Pa) in comparison with the unruptured ones (6.31 ± 6.47 Pa) (P < .01).

Conclusion

A comparison of hemodynamic properties between ruptured and unruptured small ICA-Oph aneurysms found that some hemodynamic properties vary between small aneurysms although they are similar in size and share the same anatomical location. In particular, WSS may be a useful hemodynamic factor for studying small aneurysm rupture.

Introduction

In general, prophylactic treatment of unruptured brain aneurysms remains controversial [9], [11], [14], [25], [26], [27]. International studies have shown that the risk of aneurysm rupture increases as the aneurysm size increases, supporting treatment of larger aneurysms [27]. On the other hand, many small aneurysms are observed conservatively due to the lower risk of rupture compared with the risk of morbidity and mortality related to treatments. Recent advancements in medical imaging technology have helped the early detection of unruptured brain aneurysms, and more small aneurysms are found before rupture [2], [14]. Among conservatively observed small brain aneurysms, some grow over time with a corresponding increase in the risk of rupture; however, reports have also shown that certain small aneurysms rupture without evidence of any growth [8], [13], [25]. Although they are similar in diameter, it appears that a subpopulation of small brain aneurysms possess a different rupture risk than others. Identification of small brain aneurysms at high risk for rupture is crucial for evaluating the risks of inaction and treatment [9], [15].

Intraaneurysmal hemodynamics has been intensively studied to understand the etiology and natural history of brain aneurysms. In the last decade, a variety of intraaneurysmal hemodynamic research has been published that shows the importance of intraaneurysmal flow characteristics [3], [4], [6], [12], [19], [20], [22], [24]. Using patient-specific angiographic data for flow simulation, recent flow analysis studies have suggested that certain hemodynamic parameters, such as flow pattern, flow impingement, and wall shear stress can be used to evaluate the risk of aneurysm rupture [5], [19], [20], [24].

The objective of this research is to use patient-specific hemodynamic simulation to study small aneurysm rupture. Because hemodynamic results are sensitive to aneurysm anatomical location [1], [16], to minimize its influence, we compared flow characteristics between ruptured and unruptured small aneurysms at the same anatomical location.

Section snippets

Case selection

To include as many cases as possible from a single location, we studied the internal carotid artery-ophthalmic artery (ICA-Oph) aneurysm, the most common aneurysm location in our database [17]. A total of 276 patients with ICA-Oph aneurysms who underwent endovascular treatment in the Division of Interventional Neuroradiology, University of California, Los Angeles, Medical Center, from 1996 to 2008 (May) were screened. Patients having angiographic images acquired with sufficient 3-dimensional

Blood flow characteristics

Flow patterns at the peak of pulsatile flow are shown in Fig. 2. Cases 1 to 4 and cases 5 to 8 are ruptured and unruptured aneurysms, respectively. All of the unruptured aneurysms had blood inflow into the aneurysm forming a single vortex. In the ruptured cases, only one had a single vortex (case 2); the other aneurysms had blood inflow with multiple associated vortices (Table 1). Five aneurysms had blood flow impinging at the neck (3 ruptured and 2 unruptured), 2 at the body (1 ruptured and 1

Discussion

Development of aneurysms is associated with the vascular wall response to various hemodynamic stresses [18], [19], [23]. Using experimental measurement or computer simulation, hemodynamic parameters such as the flow velocity and WSS can be obtained based on fluid dynamics principles. These hemodynamic parameters may help determine not only the mechanical effect of blood flow on the vessels but also how the molecular response within the vessel wall is associated with the physical forces caused

Conclusion

Hemodynamic analyses of small aneurysms enabled us to compare the detailed blood flow characteristics between ruptured and unruptured cases. We found that not all aneurysms that are small share the same hemodynamic properties. Among the characteristics investigated, the value of WSS in an aneurysm sac was the only hemodynamic parameter that showed statistical differences between ruptured and unruptured aneurysms.

References (28)

  • DhaliwalS. et al.
  • DonnanG.A. et al.

    Patients with small, asymptomatic, unruptured intracranial aneurysms and no history of subarachnoid hemorrhage should be treated conservatively

    Stroke

    (2005)
  • HumphreyJ.D.

    Vascular adaptation and mechanical homeostasis at tissue, cellular, and sub-cellular levels

    Cell Biochem Biophys

    (2008)
  • JohnstonS.C. et al.

    Which unruptured cerebral aneurysms should be treated? A cost-utility analysis

    Neurology

    (1999)
  • Cited by (0)

    View full text