Layered collagen fabric of cerebral aneurysms quantitatively assessed by the universal stage and polarized light microscopy

Abstract

We evaluated the effectiveness of the Universal stage, an instrument for measuring three-dimensional orientation of birefringent materials, for studying the collagen fabric in the wall of brain aneurysms. Vessels from autopsy were fixed at normal arterial distending pressure with 10% formalin, and prepared for polarized light microscopy, with paraffin embedding and staining with picrosirius red for birefringent enhancement. Quantitative data were obtained from tangential and oblique sections (7 microns thickness) of an intact 8 mm aneurysm, a 1.5 mm aneurysm, and a tangential section (3 microns thickness) of a cerebral artery. Sections of full-size aneurysms seen through the microscope, adjusted either for plane or circularly polarized light, revealed distinctive layers of collagen across the aneurysmal wall, which at higher magnification were further subdivided. Three-dimensional measurements, numbering 1,082, were made by use of the Universal stage attachment to the polarizing microscope. They were plotted by computer-controlled graphics on Lambert projections and analyzed by circular statistics. When assessed layer by layer, the collagen spanned a full range of orientations relative to the tangential plane. The circular standard deviation, a measure of the spread of alignment about the mean, was as low as 10 degrees for coherently organized collagen and as high as 40 degrees for the least coherently organized collagen, values characteristic of either the organized tunica media, or the least organized tunica adventitia of cerebral arteries. Although there was a marked thinning of the wall of one aneurysm, there was no evidence of structural weakness based only on the directional organization assessed by our measurements.

Determination of the layer-specific distributed collagen fibre orientations in human thoracic and abdominal aortas and common iliac arteries

“…While the significance of collagen fibre orientation and dispersion on the mechanical properties of arterial walls have been well established [18,22,23], and twoand three-dimensional data of collagen organization for human vessels have been published [5,[24][25][26][27], limited structural data are available to date regarding collagen orientation in the human aorta and common iliac artery. In young and healthy arteries, the intima consists of a single layer of endothelial cells with no structural importance to the wall.…”

“…The approach taken in this study differs from related research on cerebral arteries [23,25] and intracranial aneurysms [5,27], where investigations into the collagen fibre orientations were performed. We use the wellestablished method of picrosirius-polarization [36,37], in combination with a universal stage, similar to the method pioneered and described in Smith et al [38], to study samples from healthy, non-atherosclerotic, human aortas and common iliac arteries for, to our knowledge, the first time.…”

Collagen Organization in the Branching Region of Human Brain Arteries

“…15,16 The universal stage is mounted on the main rotating stage of the microscope and permits the tissue slide to be tipped and rotated in oblique planes, with all rotational displacements calibrated. Thus, the 2 angles that define the orientation of a fiber of collagen in 3-dimensional space, ie, the azimuthal angle (in the plane of the stage) and the elevation angle (out of the plane of the stage), are recorded for each fiber measured within the tissue section.…”

Quantitative assessment of collagen fibre orientations from two-dimensional images of soft biological tissues

“…To account for the effect of strain on changes in the fibre orientations and the angular distributions, to approximate the in vivo strain state of arteries and to ensure more straightened fibres necessary for angular measurements, the investigated samples were usually either pressurized or pre-stretched biaxially beforehand [8,19,57,58]. Our approach allows us for a fast and automated determination of the angular distribution from twodimensional images.…”