The value of MRCP in children with biliary symptomatology - an essential adjunct for safe cholecystectomy

Congenital abnormalities of the biliary system are a consideration in children with biliary symptomatology. The preoperative diagnosis rate is still not satisfactory, despite progresses made in imaging technology, with the potential of biliary tract injury if surgery is indicated. The double gallbladder is a rare developmental abnormality of the biliary tract with several anatomical variations. This abnormality was accurately delineated in a 7-year-old child by MRI/MRCP, allowing the ductal anatomy to be accurately identified and safe laparoscopic cholecystectomies to be performed.

Effects of red blood cell aggregation on the blood flow in a symmetrical stenosed microvessel

In order to figure out whether red blood cell (RBC) aggregation is beneficial or deleterious for the blood flow through a stenosis, fluid mechanics of a microvascular stenosis was examined through simulating the dynamics of deformable red blood cells suspended in plasma using dissipative particle dynamics. The spatial variation in time-averaged cell-free layer (CFL) thickness and velocity profiles indicated that the blood flow exhibits asymmetry along the flow direction. The RBC accumulation occurs upstream the stenosis, leading to a thinner CFL and reduced flow velocity. Therefore, the emergence of stenosis produces an increased blood flow resistance. In addition, an enhanced Fahraeus-Lindqvist effect was observed in the presence of the stenosis. Finally, the effect of RBC aggregation combined with decreased stenosis on the blood flow was investigated. The findings showed that when the RBC clusters pass through the stenosis with a throat comparable to the RBC core in diameter, the blood flow resistance decreases with increasing intercellular interaction strength. But if the RBC core is larger and even several times than the throat, the blood flow resistance increases largely under strong RBC aggregation, which may contribute to the mechanism of the microthrombus formation.

Effects of flowing RBCs on adhesion of a circulating tumor cell in microvessels

Adhesion of circulating tumor cells (CTCs) to the microvessel wall largely depends on the blood hydrodynamic conditions, one of which is the blood viscosity. Since blood is a non-Newtonian fluid, whose viscosity increases with hematocrit, in the microvessels at low shear rate. In this study, the effects of hematocrit, vessel size, flow rate and red blood cell (RBC) aggregation on adhesion of a CTC in the microvessels were numerically investigated using dissipative particle dynamics. The membrane of cells was represented by a spring-based network connected by elastic springs to characterize its deformation. RBC aggregation was modeled by a Morse potential function based on depletion-mediated assumption, and the adhesion of the CTC to the vessel wall was achieved by the interactions between receptors and ligands at the CTC and those at the endothelial cells forming the vessel wall. The results demonstrated that in the microvessel of [Formula: see text] diameter, the CTC has an increasing probability of adhesion with the hematocrit due to a growing wall-directed force, resulting in a larger number of receptor-ligand bonds formed on the cell surface. However, with the increase in microvessel size, an enhanced lift force at higher hematocrit detaches the initial adherent CTC quickly. If the microvessel is comparable to the CTC in diameter, CTC adhesion is independent of Hct. In addition, the velocity of CTC is larger than the average blood flow velocity in smaller microvessels and the relative velocity of CTC decreases with the increase in microvessel size. An increased blood flow resistance in the presence of CTC was also found. Moreover, it was found that the large deformation induced by high flow rate and the presence of aggregation promote the adhesion of CTC.

Application of retrograde dissection method for isolation of bone marrow cells from rat femurs and tibiae

Currently, there is no practical and efficient method for the isolation of bone marrow cells (BMCs) from rat femurs and tibiae. Here, we attempted to develop a rapid, simple, effective, and non-contaminating method for the isolation of BMCs from rat femurs and tibiae. Rat femurs and tibiae were dissected from the ankle to the hip joint; subsequently, a three-step "locate-slide-twist" procedure was performed using scissors and forceps to remove the femurs and tibiae completely, from the surrounding musculature. The bones were flushed with phosphate-buffered saline to harvest BMCs. The femurs and tibiae were dissected in 1.8 ± 0.6 min, and the BMC suspension preparation time was 13.1 ± 2.3 min. The bone marrow cavities did not incur any fractures or injuries during the isolation. Culture of harvested BMCs for 72 h led to a significant increase in cell number from 4.4 ± 0.3 x 106 to 6.9 ± 0.7 x 10(6) (P < 0.01) with no significant decrease in viability (98.1 ± 0.6% vs 96.2 ± 1.1%; P > 0.05). Microscopic examination of the isolated BMCs after the 72-h incubation period revealed the no-microbial or muscle cell contamination. Furthermore, flow cytometry revealed that cultured BMCs (72-h culture) grew well. Here, we have reported a rapid, simple, effective, and non-contaminating method for the isolation of BMCs from rat femurs and tibiae by using retrograde dissection. This method can be used to harvest a large number of viable BMCs without the risk of contamination from muscle and connective tissues.

Numerical simulation of a single cell passing through a narrow slit

The narrow slit between endothelial cells that line the microvessel wall is the principal pathway for tumor cell extravasation to the surrounding tissue. To understand this crucial step for tumor hematogenous metastasis, we used dissipative particle dynamics method to investigate an individual cell passing through a narrow slit numerically. The cell membrane was simulated by a spring-based network model which can separate the internal cytoplasm and surrounding fluid. The effects of the cell elasticity, cell shape, nucleus and slit size on the cell transmigration through the slit were investigated. Under a fixed driving force, the cell with higher elasticity can be elongated more and pass faster through the slit. When the slit width decreases to 2/3 of the cell diameter, the spherical cell becomes jammed despite reducing its elasticity modulus by 10 times. However, transforming the cell from a spherical to ellipsoidal shape and increasing the cell surface area by merely 9.3 % can enable the cell to pass through the narrow slit. Therefore, the cell shape and surface area increase play a more important role than the cell elasticity in cell passing through the narrow slit. In addition, the simulation results indicate that the cell migration velocity decreases during entrance but increases during exit of the slit, which is qualitatively in agreement with the experimental observation.

Effects of wall shear stress and its gradient on tumor cell adhesion in curved microvessels

Tumor cell adhesion to vessel walls in the microcirculation is one critical step in cancer metastasis. In this paper, the hypothesis that tumor cells prefer to adhere at the microvessels with localized shear stresses and their gradients, such as in the curved microvessels, was examined both experimentally and computationally. Our in vivo experiments were performed on the microvessels (post-capillary venules, 30-50 μm diameter) of rat mesentery. A straight or curved microvessel was cannulated and perfused with tumor cells by a glass micropipette at a velocity of ~1mm/s. At less than 10 min after perfusion, there was a significant difference in cell adhesion to the straight and curved vessel walls. In 60 min, the averaged adhesion rate in the curved vessels (n = 14) was ~1.5-fold of that in the straight vessels (n = 19). In 51 curved segments, 45% of cell adhesion was initiated at the inner side, 25% at outer side, and 30% at both sides of the curved vessels. To investigate the mechanical mechanism by which tumor cells prefer adhering at curved sites, we performed a computational study, in which the fluid dynamics was carried out by the lattice Boltzmann method , and the tumor cell dynamics was governed by the Newton's law of translation and rotation. A modified adhesive dynamics model that included the influence of wall shear stress/gradient on the association/dissociation rates of tumor cell adhesion was proposed, in which the positive wall shear stress/gradient jump would enhance tumor cell adhesion while the negative wall shear stress/gradient jump would weaken tumor cell adhesion. It was found that the wall shear stress/gradient, over a threshold, had significant contribution to tumor cell adhesion by activating or inactivating cell adhesion molecules. Our results elucidated why the tumor cell adhesion prefers to occur at the positive curvature of curved microvessels with very low Reynolds number (in the order of 10(-2)) laminar flow.

Test of a two-pathway model for small-solute exchange across the capillary wall

We previously proposed a two-pathway model for solute and water transport across vascular endothelium (Fu, B. M., R. Tsay, F. E. Curry, and S. Weinbaum. J. Biomech. Eng. 116: 502-513, 1994) that hypothesized the existence of a continuous slit 2 nm wide along tight junction strands within the interendothelial cleft in parallel with 20 x 150-nm breaks in tight junctions. We tested this model by measuring capillary permeability coefficients (P) to a small solute (sodium fluorescein, radius 0.45 nm), assumed to permeate primarily the 2-nm small pore, and an intermediate-sized solute (FITC-alpha-lactalbumin, radius 2.01 nm) excluded from the small pore. Mean values of the paired diffusive permeability coefficients, Psodium fluorescein and PFITC-alpha-lactalbumin, were 34.4 and 2.9 x 10(-6) cm/s, respectively, after corrections for solvent drag and free dye (n = 26). These permeabilities were accounted for by transport through the large-break pathway without the additional capacity of the hypothetical 2-nm pathway. As a further test we examined the relative reductions of Psodium fluorescein and PFITC-alpha-lactalbumin produced by elevated intracellular cAMP. Within 20 min after the introduction of rolipram and forskolin, Psodium fluorescein and PFITC-alpha-lactalbumin decreased to 0.67 and 0.64 times their respective baseline values. These similar responses to permeability decrease were evidence that the two solutes were carried by a common pathway. Combined results in both control and reduced permeability states did not support the hypothesis that a separate pathway across tight junctions is available for solutes with a radius as large as 0.75 nm. If such a pathway is present, then its size must be smaller than that of sodium fluorescein.

A diffusion wake model for tracer ultrastructure-permeability studies in microvessels

We developed a time-dependent diffusion model for analyzing the concentration profiles of low-molecular-weight tracers in the interendothelial clefts of the capillary wall that takes into account the three-dimensional time-dependent filling of the surrounding tissue space. The model provides a connecting link between two methods to investigate transvascular exchange: electron-microscopic experiments to study the time-dependent wake formed by low-molecular-weight tracers (such as lanthanum nitrate) on the tissue side of the junction strand discontinuities in the interendothelial cleft of frog mesentery capillaries (R. H. Adamson and C. C. Michel. J. Physiol. Lond. 466: 303-327, 1993) and confocal-microscopic experiments to measure the spread of low-molecular-weight fluorescent tracers in the tissue space surrounding these microvessels (R. H. Adamson, J. F. Lenz, and F. E. Curry, Microcirculation 1: 251-265, 1994). We show that the interpretation of the presence of tracer as an all-or-none indication of a pathway across the junctional strand is likely to be incorrect for small solutes. Large-pore pathways, in which the local tracer flux densities are high, reach a threshold concentration for detection and are likely to be detected after relatively short perfusion times, whereas distributed small-pore pathways may not be detected until the tissue concentrations surrounding the entire vessel approach threshold concentrations. The analysis using this approach supports the hypothesis advanced by Fu et al. (J. Biomech. Eng. 116: 502-513, 1994) that the principal pathways for water and solutes of < 1.0 nm diameter across the interendothelial cleft may be different and suggests new experiments to test this hypothesis.

A junction-orifice-fiber entrance layer model for capillary permeability: application to frog mesenteric capillaries

The recent serial section electron microscopic studies by Adamson and Michel (1993) on microves gels of frog mesentery have revealed that the large pores in the junction strand of the interendothelial cleft are widely separated 150 nm wide orifice-like breaks whose gap height 20 nm is the same as the wide part of the cleft. In this paper a modified version of the model in Weinbaum et al. (1992) is first developed in which this orifice structure is explored in combination with a random or ordered fiber matrix layer that is at the luminal surface and/or occupies a fraction of the wide part of the cleft. This basic orifice model predicts that for the measured Lp to be achieved the fiber layer must be confined to a relatively narrow region at the entrance to the cleft where it serves as the primary molecular filter. The model provides a much better fit of the permeability P for intermediate size solutes between 1 and 2 nm radius than the previous model in Weinbaum et al., where the junction strand breaks were treated as finite depth circular or rectangular pores, but like the previous model significantly underestimates P for small ions. However, it is shown that if a small frequent pore of 1.5 nm radius with characteristic spacing comparable to the diameter of the junction proteins or a continuous narrow slit of approximately 1.5 to 2.3 nm gap height is also present in the continuous part of the junction strand, small ion permeability can also be satisfied. The 1.5 nm radius pore does not significantly change Lp, whereas the continuous narrow slit provides a contribution to Lp that is comparable to, or in the case of the 2.3 nm slit greater than, the widely spaced 150 nm orifices. Thus, for the narrow slit the contribution to Lp from the orifices can be as low as 1.0 x 10(-7) cm/s/cm H2O and it is also possible to satisfy the 2.5 fold increase in permeability that occurs when the matrix is enzymatically removed from the luminal side of the cleft, Adamson (1990). The likelihood of each of these cleft structures is discussed.