Encephalometry

ENCEPHALOMETRY (from the Greek encephalon - brain and metron - measure), measurements of the brain. Macroencephalometry is the measurement of distances between various defined points on the brain surface, measurements of the width of the cortex on sections, measurements of the surface area of the entire cortex, weighing of the brain and hemispheres, and separately of the grey matter (cortex). Microencephalometry is the measurement of the size of nerve cells, cell density (the number in 1 mm³ of the cortex), the width of individual cortical layers, and the ratios of the latter to each other in various cytoarchitectonic formations. In addition, measurements are performed on the brain that require both macroscopic and microscopic investigation,

namely: measurement of the distribution area on the brain surface and in the depths of the sulci of individual cytoarchitectonic formations (see Cerebral cortex cytoarchitectonics); the percentage ratio of the surface area of a given field within a sulcus to the area located on the free surface of the gyri (designated as the intrasulcal component). Finally, methods have recently been proposed for measuring the cortical volume of individual cytoarchitectonic fields and regions. To measure the size of the cerebrum and its individual lobes, a waxed cloth centimeter tape and a craniometer with blunt ends are used; distances between individual points easily identifiable on various hemispheres are measured. For convenience of comparison, Economo proposed performing 26 standard measurements on the brain. Measurements of the brain surface area are most accurately performed by reconstruction from a continuous series of sections. The contour of each individual section is thereby transferred in an enlarged size onto paper by means of a projection apparatus and then measured with a curvimeter or a waxed thread. The volume of the cortex is obtained by measuring the cortical area on a series of sections using a planimeter, followed by addition according to a formula that takes into account the thickness of each section. The size and density of cells, and the width of the cortical layers, are determined by means of an ocular micrometer or from microphotographs. Microencephalometry requires a meticulous and uniform technique of fixation, embedding, sectioning, and staining. Encephalometry was previously understood to mean measurements performed on the skull (scalp) in order to determine thereon the projection of various cerebral sulci and and gyri (see Cranio-cerebral topography). Encephalometer, or brain topograph, are apparatuses proposed for the projection of brain gyri onto the scalp. The encephalometer of D. N. Zernov and the brain topograph of G. I. Rossolimo did not gain widespread use.