🧠 Computational Fluid Dynamics for Intracranial Aneurysms [Neurosurgery Wiki]

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====== 🧠 Computational Fluid Dynamics for Intracranial Aneurysms ======

[[Computational fluid dynamics indices of unruptured cerebral aneurysms with 3 T magnetic resonance angiography]]

**[[Computational Fluid Dynamics]] (CFD)** refers to the numerical [[simulation]] of [[blood flow]] within cerebral arteries and [[aneurysm]]s, aiming to understand [[hemodynamic]] forces that may contribute to [[aneurysm formation]], growth, and rupture.

===== 💡 Purpose =====
CFD models are used to:
  * Analyze **wall shear stress (WSS)** and **oscillatory shear index (OSI)**
  * Identify **high-risk aneurysm morphologies**
  * Support treatment planning (e.g. coiling vs flow diversion)
  * Predict rupture risk in **unruptured intracranial aneurysms (UIAs)**

===== 🔬 Workflow Overview =====
  - **Image Acquisition**: CTA, MRA, or DSA
  - **3D Reconstruction**: Vascular geometry segmentation
  - **Mesh Generation**: Tetrahedral or polyhedral volume mesh
  - **Boundary Conditions**: Inlet flow rates, outlet pressures
  - **Simulation**: Navier-Stokes equations for pulsatile flow
  - **Post-Processing**: WSS, velocity fields, vorticity analysis

===== 🧪 Common Parameters =====
^ Parameter         ^ Description                                         ^
| WSS               | Force per unit area exerted by blood on the wall   |
| OSI               | Variation of WSS over the cardiac cycle            |
| RRT               | Relative residence time of particles near the wall |
| Flow Impingement | Localized high-velocity jet on aneurysm wall       |

===== ⚠️ Limitations =====
  * Highly sensitive to **geometry and boundary conditions**
  * Assumes **rigid walls** (ignores wall elasticity)
  * **Patient-specific flow data** often unavailable
  * **Validation** against clinical outcomes remains limited



----


[[Computational fluid dynamics]] (CFD) simulations are increasingly utilized to evaluate [[intracranial aneurysm]] (IA) [[hemodynamics]] to aid in the prediction of morphological changes and rupture risk. However, these [[model]]s vary and differences in published results warrant the [[investigation]] of IA-CFD reproducibility. Paritala et al aimed to explore sources of intra-team variability and determine its impact on the aneurysm [[morphology]] and CFD parameters. A team of four operators was given six sets of [[magnetic resonance angiography]] data spanning a decade from one patient with a [[middle cerebral artery aneurysm]]. All operators were given the same [[protocol]] and [[software]] for model [[reconstruction]] and numerical analysis. The morphology and hemodynamics of the operator models were then compared. The [[segmentation]], smoothing factor, inlet, and outflow branch lengths were found to cause intra-team variability. There was 80% [[reproducibility]] in the time-averaged wall shear stress distribution among operators with the major difference attributed to the level of smoothing. Based on these findings, it was concluded that the clinical applicability of CFD simulations may be feasible if a standardized segmentation protocol is developed. Moreover, when analyzing the aneurysm shape change over a decade, it was noted that the co-existence of positive and negative values of the [[wall shear stress]] divergence (WSSD) contributed to the growth of a daughter sac
((Paritala PK, Anbananthan H, Hautaniemi J, Smith M, George A, Allenby M, Mendieta JB, Wang J, Maclachlan L, Liang E, Prior M, Yarlagadda PKDV, Winter C, Li Z. Reproducibility of the computational fluid dynamic analysis of a cerebral aneurysm monitored over a decade. Sci Rep. 2023 Jan 5;13(1):219. doi: 10.1038/s41598-022-27354-w. PMID: 36604495.))
----



see [[Computational fluid dynamics for thin walled region]].


===== Case series =====

The objective of a study was to use image-based CFD simulation techniques to analyze the impact that multiple closely spaced IAs of the supra-clinioid segment of the ICA have on each other's hemodynamic characteristics. The vascular geometry of fifteen (15) subjects with 2 IAs were gathered using a 3D clinical system. Two groups of computer models were created for each subject's vascular geometry: both IAs present (Model A) and after removal of one IA (Model B). Models were separated into two groups based on IA separation: tandem (one proximal and one distal) and tandem (aneurysms directly opposite on a vessel). Simulations using a pulsatile velocity waveform were solved by a commercial CFD solver. Proximal IAs altered flow into distal IAs (5 of 7), increasing flow energy and spatial-temporally averaged wall shear stress (STA-WSS: 3-50\% comparing Model A to B) while decreasing flow stability within distal IAs. Thus, proximal IAs may ``protect" a distal aneurysm from destructive remodeling due to flow stagnation. Among adjacent IAs, the presence of both IAs decreased each other's flow characteristics, lowering WSS (Model A to B) and increasing flow stability: all changes statistically significant (t-test p < 0.05). A negative relationship exists between the mean percent change in flow stability in relation to adjacent IA volume and ostium area. Closely spaced IAs impact hemodynamic alterations onto each other concerning flow energy, stressors and stability. Understanding these alterations may improve clinical management of closely-spaced IAs
((Sunderland K, Huang Q, Strother C, Jiang J. Two closely-spaced Aneurysms of
the Supraclinoid Internal Carotid Artery: How Does One Influence the Other? J
Biomech Eng. 2019 May 29. doi: 10.1115/1.4043868. [Epub ahead of print] PubMed
PMID: 31141586.
)).
----
Liu et al., studied 27 [[paraclinoid aneurysm]]s (seven recanalized and 20 stable) treated with coils and Enterprise stents. Computational fluid dynamic simulations were performed on patient-specific aneurysm geometries using virtual stenting and porous media technology.

After stent placement in 27 cases, aneurysm flow velocity decreased significantly, the reduction gradually increasing from the neck plane (11.9%), to the residual neck (12.3%), to the aneurysm dome (16.3%). Subsequent coil embolization was performed after stent placement and the hemodynamic factors decreased further and significantly at all aneurysm regions except the neck plane. In a comparison of recanalized and stable cases, univariate analysis showed no significant differences in any parameter before treatment. After stent-assisted coiling, only the reduction in area-averaged velocity at the neck plane differed significantly between recanalized (8.1%) and stable cases (20.5%) (p=0.016).

Aneurysm flow velocity can be significantly decreased by stent placement and coil embolization. However, hemodynamics at the aneurysm neck plane is less sensitive to coils. Significant reduction in flow velocity at the neck plane may be an important factor in preventing recanalization of paraclinoid aneurysms after subtotal stent-assisted coil embolization (SACE)
((Liu J, Jing L, Wang C, Paliwal N, Wang S, Zhang Y, Xiang J, Siddiqui AH, Meng 
H, Yang X. Effect of hemodynamics on outcome of subtotally occluded paraclinoid
aneurysms after stent-assisted coil embolization. J Neurointerv Surg. 2016
Nov;8(11):1140-1147. doi: 10.1136/neurintsurg-2015-012050. PubMed PMID: 26610731;
PubMed Central PMCID: PMC4882272.
)).
----
Park et al., created paired virtual models of computational fluid dynamics (CFD) in five aneurysms which were initially regarded as having achieved complete occlusion and then recurred during follow-up. Paired virtual models consisted of the CFD model of 3D rotational angiography obtained in the recurred aneurysm and the control model of the initial, parent artery after artificial removal of the coiled and recanalized aneurysm. Using the CFD analysis of the virtual model, they analyzed the hemodynamic characteristics on the neck of each aneurysm before and after its recurrence.

High [[wall shear stress]] (WSS) was identified at the cross-sectionally identified aneurysm neck at which recurrence developed in all cases. A small vortex formation with relatively low velocity in front of the neck was also identified in four cases. The aneurysm recurrence locations corresponded to the location of high WSS and/or small vortex formation.

Recanalized aneurysms revealed increased WSS and small vortex formation at the cross-sectional neck of the aneurysm. This observation may partially explain the hemodynamic causes of future recanalization after coil embolization
((Park W, Song Y, Park KJ, Koo HW, Yang K, Suh DC. Hemodynamic Characteristics
Regarding Recanalization of Completely Coiled Aneurysms: Computational Fluid
Dynamic Analysis Using Virtual Models Comparison. Neurointervention. 2016
Mar;11(1):30-6. doi: 10.5469/neuroint.2016.11.1.30. PubMed PMID: 26958410; PubMed
Central PMCID: PMC4781914.
)).
===== Case reports =====
===2017===
Computational Fluid Dynamics of a Fatal Ruptured Anterior Communicating Artery Aneurysm
((Hejčl A, Švihlová H, Sejkorová A, Radovnický T, Adámek D, Hron J,
Dragomir-Daescu D, Málek J, Sameš M. Computational Fluid Dynamics of a Fatal
Ruptured Anterior Communicating Artery Aneurysm. J Neurol Surg A Cent Eur
Neurosurg. 2017 Aug 11. doi: 10.1055/s-0037-1604286. [Epub ahead of print] PubMed
PMID: 28800663.
)).
===2016===
Sejkorová et al., analyzed a case of a ruptured [[middle cerebral artery aneurysm]] for which they acquired imaging data at three time points, including at rupture. A patient with an observed MCA aneurysm was admitted to the emergency department with clinical symptoms of a [[subarachnoid hemorrhage]]. During three-dimensional (3D) digital subtraction angiography (DSA), the aneurysm ruptured again. Imaging data from two visits before rupture and this 3D DSA images at the moment of rupture were acquired, and [[computational fluid dynamics]] (CFD) simulations were performed. Results were used to describe the time-dependent changes of the hemodynamic variables associated with rupture. Time-dependent hemodynamic changes at the rupture location were characterized by decreased [[wall shear stress]] WSS and flow velocity magnitude. The impingement jet in the dome changed its position in time and the impingement area at follow-up moved near the rupture location. The results suggest that the increased WSS on the dome and increased low wall shear stress area (LSA) and decreased WSS on the daughter bleb with slower flow and slow vortex may be associated with rupture. CFD performed during the follow-up period may be part of diagnostic tools used to determine the risk of aneurysm rupture
((Sejkorová A, Dennis KD, Švihlová H, Petr O, Lanzino G, Hejčl A,
Dragomir-Daescu D. Hemodynamic changes in a middle cerebral artery aneurysm at
follow-up times before and after its rupture: a case report and a review of the
literature. Neurosurg Rev. 2016 Nov 24. [Epub ahead of print] PubMed PMID:
27882440.
)).
----

A 75-year-old male patient underwent [[magnetic resonance angiography]], which revealed a large internal carotid artery aneurysm with inflow jet inside the aneurysm. The aneurysm was stable for 18 months, but a new daughter sac developed at the tip of the aneurysm during the next 6 months. The daughter sac seemed to be related to the inflow jet on MR angiography. Aneurysm geometries before and after daughter sac formation were reconstructed using the longitudinal data of MR angiography. Computational fluid dynamic simulations were conducted under the patient-specific pulsatile inlet conditions measured by MR velocimetry.

The hemodynamic simulation revealed that the inflow jet impinged on two sites of the aneurysm: the right side of the aneurysmal dome and tip of the aneurysm. The flow impingement caused elevation of pressure at both sites. However, the daughter sac formed at the latter site surrounded by basal cistern, but did not form at the former site that was in contact with the right temporal lobe.

Blood inflow jet caused local elevation of pressure, and the formation of the daughter sac occurred at the site with high pressure but without the surrounding structure that may cancel the perpendicular wall tension
((Sugiyama SI, Endo H, Omodaka S, Endo T, Niizuma K, Rashad S, Nakayama T,
Funamoto K, Ohta M, Tominaga T. Daughter sac formation related to blood inflow
jet in an [[intracranial aneurysm]]: A case study. World Neurosurg. 2016 Sep 16. pii:
S1878-8750(16)30866-X. doi: 10.1016/j.wneu.2016.09.040. [Epub ahead of print]
PubMed PMID: 27647032.
)).
===== References =====