Squama
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Citation: Grzonkowska M, Baumgart M, Badura M, Wiśniewski M, Szpinda M (2021) Quantitative anatomy of the fused ossification center of the occipital squama in the human fetus. PLoS ONE 16(2): e0247601.
Although the timing of ossification of each bone in the skull is recognized, no morphometric measurements involving the use of CT examinations of the occipital ossification centers have been reported. This is the first report in the literature to analyze morphometric parameters of the occipital squama ossification centers in human fetuses based on computed tomography imaging.
Mean values and standard deviations of the analyzed parameters of the occipital squama ossification centers in human fetuses at the analyzed gestational ages are presented in Tables 3 and 4 for the vertical (right and left) and transverse diameters of the interparietal and supraoccipital parts, projection surface area and volume.
The mean projection surface area of the occipital squama ossification center ranged from 175.70 13.12mm2 at 18 weeks to 724.33 31.76mm2at 30 weeks of gestational age, following the logarithmic function: y = -3062.89 + 1108.98 ln(age) 29.476 R2 = 0.98 (Fig 4C).
This paper is the first report in the professional literature to precisely analyze morphometric parameters of the occipital squama ossification center in human fetuses with mathematical growth models. The right and left vertical diameters of the occipital squama ossification center followed linear functions, therefore grew proportionately to gestational age in weeks, which proved an intense and dynamic growth of this ossification center between 18 and 30 weeks of gestational age. In turn, the transverse diameters of the supraoccipital and interparietal parts, as well as the projection surface area of the occipital squama ossification center followed natural logarithmic functions, with gestational age expressed in weeks. In the studied period, a logarithmic increase of the parameters studied indicates an intensive development: up to 27 weeks of gestation for the interparietal part, up to 26 weeks of gestation for the supraoccipital part, and up to 28 weeks for projection surface area of the occipital squama ossification center. Gradual inhibition of growth in the subsequent weeks of development. Moreover, in the analyzed period, the mean transverse diameter of the interparietal part was 20 percent larger than that of the supraoccipital part. The study also revealed that the volume of the occipital squama ossification center increased in accordance with a quadratic function of gestational age. In a study on the development of the frontal squama ossification center in human fetuses, the growth dynamics regarding its vertical diameter, projection surface area and volume followed the quadratic functions: y = 13.756 + 0.021 age2 0.024, y = 38.285 + 0.889 age2 0.034, and y = -90.756 + 1.375 age2 11.44, respectively. In turn the transverse diameter increased in a manner directly proportionate to gestational age, following the linear function:y = 0.956 + 0.956 age 0.823 [19].
The dimensions of the occipital squama ossification center obtained in the present study may be potentially useful in diagnosing skeletal dysplasias that are often characterized by a disrupted or completely halted growth of the occipital bone in the fetus. Our numerical data referring to the occipital squama ossification center may be relevant in monitoring normal fetal growth and screening for congenital disorders. Skeletal dysplasias also involve other bones of the neurocranium (frontal, parietal, and occipital) and their ossification along with development of the neural tube. Disturbances of the ossification process may result in separation of two parts of the occipital squama by the transverse occipital suture at the level of the supreme nuchal line [8, 11] In such cases, the separate interparietal part constitutes a discrete bone called an Inca bone or an interparietal bone [3, 1
