A growth model of saccular aneurysms based on hemodynamic and morphologic discriminant parameters for risk of rupture

The aim of this study was to derive a model describing the evolution of bifurcation type cerebral aneurysms based on morphological and hemodynamic parameters. Idealized bifurcation models were constructed based on the two morphological parameters of aspect ratio (AR) and size ratio (SR). Aneurysm development was investigated according to the following four patterns: R1, increasing SR with constant AR; R2, increasing AR with constant SR; R3, increasing SR and increasing AR; R4, increasing AR with constant parent artery diameter. Relationships were obtained between energy loss (EL) and morphological parameters (EL-SR and EL-AR curves). The curves were validated by mapping the growth of a ruptured patient-specific bifurcation aneurysm at three stages of follow-up. EL increased in parallel with growth patterns R1 and R3, whereas growth pattern R2 showed a decrease in EL. No significant changes were observed in EL when the growth of the aneurysm was associated only with changes in aneurysm size and independent of changes in parent artery diameter and main flow (R4). Changes in parent artery diameter of bifurcation aneurysms resulted in significant variation in EL. Mapping the growth of a follow-up aneurysm onto the EL-AR curve demonstrated that aneurysms with increasing EL during the observation period are at higher risk of rupture than aneurysms with decreasing EL. Based on the proposed growth model, assessment of morphological (AR and SR) and hemodynamic (EL) parameters may provide quantifiable information on the risk of bifurcation aneurysm rupture during clinical patient follow-up.

Effect of bifurcation angle configuration and ratio of daughter diameters on hemodynamics of bifurcation aneurysms

BACKGROUND AND PURPOSE

EL associated with ruptured aneurysms is higher than that for unruptured aneurysms. In this study, the effect of arterial morphologic variation of bifurcation aneurysms on EL was investigated in idealized models of middle cerebral artery aneurysms.

MATERIALS AND METHODS

Bifurcation angle configuration and DA ratio were evaluated in 6 idealized numeric models. Type A and B bifurcation models were defined with symmetric and asymmetric bifurcation angles of 136°, and 57° and 79°, respectively. Three models with DA ratios of 1, 1.3, and 2 were constructed for each type. EL was calculated as the energy difference between aneurysm inflow and outflow at the aneurysm neck. Three growth paths (R1, R2, and R3) were proposed.

RESULTS

The highest EL and influx occurred in bifurcations with DA ratios of 1 for both types A and B. As the DA ratio increases, flow distribution between branches becomes more asymmetric, resulting in a reduction of EL and intra-aneurysmal flow. No strong relation was found between bifurcation angle configuration, inflow flux, and EL. EL decreased with an increase in the AR and DA ratio and increased with an increase in the AR and reduction of DA ratio.

CONCLUSIONS

EL determined in idealized models is less dependent on bifurcation angle configuration than on DA ratio, and the stability of the aneurysm strongly depends on variation of the daughter artery morphology after aneurysm growth.

Effect of inflow on computational fluid dynamic simulation of cerebral bifurcation aneurysms

Morphological characteristics associated with cerebral aneurysm formation can be used to assess aneurysm rupture. This study investigated hemodynamic effects resulting from change in the parent artery diameter of bifurcation type aneurysm. Computational fluid dynamic (CFD) analysis was performed on middle cerebral artery (MCA) models with various parent artery diameters. Calculations were performed with steady flow rate (125 ± 12.5 ml/min) at the parent artery inlet. Energy loss (EL) was calculated from pressure and kinetic energy obtained from flow velocity. The results indicate that the high wall shear stress (WSS) and EL occurs in model with the smallest parent vessel compared to the other models for all three inflows. Results also showed that 10% variation of inflow results in average of 23 ± 2.9% changes in WSS and 25.5 ± 0.5% changes in energy loss. These results demonstrated that for CFD analysis of MCA bifurcation type aneurysm, upstream parent vessel and inflow evaluation for individual patient is essential.

Effect of saccular aneurysm and parent artery morphology on hemodynamics of cerebral bifurcation aneurysms

Morphological descriptors of aneurysms have been used to assess aneurysm rupture. This study investigated the relation between the morphological parameters and the flow related parameter of energy loss (EL). Four size indices and one shape index were assessed in idealized middle cerebral artery models with various aneurysm morphologies. Four patient-specific aneurysms (2 ruptured, 2 unruptured) were virtually manipulated by removing the aneurysms from their parent arteries and merging them with the idealized bifurcation models. EL was calculated from the energy difference between inflow and outflow. The results indicate that among size indices, EL is mostly dependent on bottleneck factor and less dependent on the aspect ratio. Results also showed that there is a direct relationship between nonsphericity index (NSI) and EL in manipulated models. No specific correlation was found between EL and NSI in patient-specific models.

Hemodynamic models of cerebral aneurysms for assessment of effect of vessel geometry on risk of rupture

Surgical decisions on treatment of cerebral aneurysms are based predominantly on aneurysm size. This study has assessed the influence of parent vessel geometry on intra-aneurysmal flow patterns and mass flow rate using computational fluid dynamics and finite element modeling of straight and curved vessels feeding saccular aneurysms of varying size and aspect ratio. Simulation results have shown that aneurysms of similar shape and size but with curved parent vessels can have more than 2 fold increase in flow rate, with markedly different flow velocity patterns and development of secondary flows. These are significant hemodynamic factors that can contribute to increased risk of aneurysm rupture, in addition to aneurysm size. The dependency of parent vessel geometry is a function of aneurysm aspect ratio and shows minimal dependency at an aspect ratio of 1.68. These findings could be used for improved quantification of risk of rupture of cerebral aneurysms detected from clinical imaging modalities and to aid surgical decision making.

Current status of periodontal dressings

A comprehensive review of periodontal dressings is presented. The rationale for the application of dressings, their advantages and disadvantages are described. Tissue reactions to dressings and the therapeutic and adverse effects of antimicrobial agents used in dressings are discussed. The present status and value of a surgical dressing is critically assessed in view of recent studies which indicate that the routine use of dressings in postsurgical care may be either unnecessary or undesirable.

Proliferation of mast cells in normal and DMBA-treated mouse skin

To examine the pattern of proliferation of mast cells in the skin of Swiss Webster mice, single or multiple pulses of 3H-thymidine, autoradiography and selective staining techniques were combined to detect DNA synthesis. A very low labelling index was found for the mast cells of normal skin but alteration of the mast-cell population using the chemical carcinogen dimethylbenzathracene led to increased labelling of mast cells. A series of studies of experimentally altered skin showed a pattern of mast cell labelling which suggested derivation of new mast cells by local self-replication. The labelling pattern indicated that mast cells labelled after 1 h divided to produce 2 daughter cells and that the rate of increase in the number of labelled mast cells following repeated labelling for up to 20 days was linear. These data do not suggest major recruitment of mast cells from a distant source during this period.

Sequential histological changes and mast cell response in skin during chemically-induced carcinogenesis

Skin tumors experimentally induced by dimethylbenzanthracene (DMBA) are associated with dense subepithelial accumulations of mast cells. To investigate the sequential changes of the mast cell population during carcinogenesis, and to provide a model with which to examine mast cell proliferation, the back skin of 48 Swiss Webster mice was painted with 0.5% DMBA in benzene twice weekly for 12 weeks. Control and DMBA-treated tissues were processed for histological examination. The observed pattern of tissue changes fell into four phases: a) inflammation and necrosis followed by epithelial regeneration and hyperplasia, b) development of localized regions of acanthosis, c) loss of normal organization with downgrowth of epithelial cells and formation of keratin pearls, d) appearance of well-defined nodules resembling verrucous carcinoma. Subepithelial mast cells varied greatly in number during the above sequence of changes. Dense foci of cells were seen, particularly beneath the regions of hyperplastic epithelium. Mast cells may play a role in abnormal epithelial proliferation and, further, DMBA treatment may provide a suitable model with which to examine the origin and kinetics of mast cells.

Techniques for the protection and coverage of the donor sites in free soft tissue grafts

Palatal donor sites used for free soft tissue grafts are commonly left exposed during healing which occurs by secondary intention. This often results in postoperative discomfort and pain and in some cases apparent delayed healing of the donor sites. Various techniques for the protection and coverage of donor sites have been presented and the rationale, advantages and disadvantages of coverage of gingival wounds have been discussed.

The application of an image analyzing computer (Quantimet 720) for quantitation of biological structures--the automatic counting of mast cells

A Quantimet 720 image analyzer was utilized in order to 1) quantify mast cells automatically in gingiva and in doing so to 2) investigate the applicability and accuracy of the machine for quantitative analysis of biological structures. The mast cells of two hundred gingival sections were counted first by means of the Quantimet and then by manual count. Results indicated that a) mean counts of mast cells obtained by means of the Quantimet were comparable to that of the manual counts, b) although the spread was larger than by manual methods, the Quantimet automatic image analyzer performed quantitation more rapidly.