Planar measurements of foetal lateral ventricles

To compare the linear dimensions (width) of the foetal atrium and occipital horns to their areas, 31 foetuses (15–24 weeks, C-R 12.5–23.5 mm) from spontaneous abortions were evaluated. Images of the axial sections of the brains were transferred to computer and Scion for Windows 98 software was used for image analysis. 11 brains appeared normal and 20 were abnormal (leukomalacia in 9 cases, periventricular and intraventricular haemorrhage in 6 cases, ventriculomegaly in 3 cases, colpocephaly in 1 case, vascular malformation in 1 case). High-range linear and planar asymmetries in the atrium and occipital horns were observed both in normal and abnormal brains. There was no close correlation between the width and the area of the structures under investigation, although it was stronger in case of the occipital horns. The wider occipital horns and atria often had a smaller area than the narrower ones. Some abnormal cerebral hemispheres had relatively narrow atria and occipital horns in comparison with their large areas. Further investigation should be carried out to assess the utility and potential superiority of planar measurements over linear in the image diagnosis of foetal ventricles

Clinical anatomy of the human anterior cranial fossa during the prenatal period

We examined the prenatal development of the human anterior cranial fossa and considered its clinical aspects. Our purpose was an evaluation of anterior cranial fossa geometry, its measurements and connections with the nasal cavity and middle cranial fossa. The study was performed on 29 foetuses from the first and second trimester of pregnancy. New methods of computer image analysis, Scion for Windows 98 and ELF v 4.2, were applied to examine this anatomical region. Different options used were binarisation, equalisation, filters, linear and non-linear transformations and mathematical operations of images. This enabled the dynamics of prenatal development to be accurately evaluated for parts of the base of the human skull. Measurements were taken of angles of the cranial base. The anterior cranial base angle (the apex in the middle of the sella turcica and the arms running through the zygomatic ossification points) decreased gradually between C-R 6 to 23.5 cm from 170 to 120 degrees and afterwards became constant. The contrary-medial cranial base angle (adjacent to the anterior cranial base angle and with a second arm running through the auricular cartilage) increased from 50 to 70 degrees. The anterior cranial fossa was first located on the same level as the middle and posterior fossae. The process of descent of the middle and posterior cranial fossa begins in the 4th gestational month. The geometry of the anterior cranial fossa changes rapidly, especially in the first trimester of pregnancy. The first trimester of pregnancy is crucial for the development of its defects. Preconception prophylaxis of inborn defects of the anterior cranial fossa is therefore extremely important

Partial dissolution of glauconitic samples : Implications for the methodology of K-Ar and Rb-Sr dating

The K-Ar dating of glauconite has been used as an important stratigraphic tool for many decades. The application of this technique is limited to pure glauconites, free of detrital contamination by K-bearing phases, often not easy to detect. This study extends the application of isotope dating to the contaminated glauconites and offers a precise technique for detecting the detrital contamination of glauconites. The most common K-bearing detrital contaminants have smaller (K-feldspars, Al-rich dioctahedral micas) or greater (trioctahedral micas) dissolution rates than glauconite in extremely low pH solutions. The differences in the dissolution rates can be applied to evaluate the purity of the glauconite and its crystallization age. The interlaboratory GLO glauconite standard and grain-size fractions separated from glauconitic sandstones of the Paleogene (sample GL) and Jurassic (sample GW8) ages were treated with acid (3 M HCl, at 99±2°C) for different reaction times (0.5-7 h) and measured for their apparent isotopic ages. Microporous amorphous silica with large specific surface area is the solid product of the reaction and its content increases with reaction time. The K-Ar dates (apparent ages) of the solid residues increase significantly with reaction time: from 44.6 to 107 Ma for the GL sample and from 125.7 to 394.7 Ma for GW8. The increase is negligible in the case of the GLO standard. The Rb-Sr data of the GL sample were modeled using initial 87Sr/86Sr ratios of 0.707-0.709, which resulted in a 29.9-35.8 Ma date for the untreated portions of GL, and ∼42.6 Ma after 7 h of treatment. The increase of isotopic K-Ar date with increasing time of dissolution is interpreted to be a result of increasing concentration of detrital, acid-resistant, K-bearing minerals, observed also with the electron microscope and X-ray diffraction. Probabilistic modeling based on single (K-Ar) or double (K-Ar and Rb-Sr) isotopic systems evaluated the isotopic ages of the detrital and authigenic minerals, and their K2O and Rb concentrations. The crystallization ages computed using these two methods are: 24.0, 26.5, and 32.3 Ma for the GL material, and 117.3-121.8 Ma for the GW8 series. The proposed method based on partial dissolution is a potential tool for evaluating the reliability of glauconite dating