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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.
Variations of the dural folds and the dural venous sinuses are seldom reported in the extant medical literature. Such variations in the posterior cranial fossa may be problematic in various diagnostic and operative procedures of this region. We report our observation of an extremely rare variation of the falx cerebelli and posterior cranial fossa venous sinuses encountered upon dissection of a young male cadaver. In this specimen the falx cerebelli was duplicated with dimensions of 45.3 × 5.1 mm and 49.8 × 5.3 mm for the right and left falces respectively. The distance between the two falces was 3.2, 4.5 and 7.8 mm at their proximal, middle and distal thirds. An accessory small falx (31.8 × 2 mm) was also found approximately 3.4 mm lateral to the right falx cerebelli and blended with the lateral surface of the right falx cerebelli. There was only one occipital venous sinus (diameter, 2.5 mm) and no marginal sinus was detected. At the right floor of the posterior cranial fossa (posterolateral to the foramen magnum) an additional dural venous sinus was found, which connected the terminal portion of the right sigmoid sinus to the occipital and right transverse sinuses via one medial and two lateral branches respectively. We believe that such a complex dural-venous variation in the posterior cranial fossa has not previously been reported. Neurosurgeons and neuroradiologists should be aware of such variations, as these could be potential sources of haemorrhage during suboccipital approaches or may lead to erroneous interpretations of imaging of the posterior cranial fossa.
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