GROWTH IN THE LATERAL PART OF THE HUMAN SKULL DURING THE 2ND-TRIMESTER

The aim of the present study was to report dimensional changes in the lateral part of the prenatal human skull during the second trimester. The sample comprised 37 fetuses obtained in connection with requested autopsy. Gestational ages (GA) were available for 27 fetuses, ranging from 13 to 24 weeks. Crown-rump lengths (CRL) of 23 fetuses ranged fro m 78 to 228 mm. For 21 fetuses both CRL and GA were available. After e xcision of the midsagittal segment of the skulls by two paramedian sec tions from the frontal bone to the foramen magnum through the optic fo ramina, an incision was made through the middle of the occipital squam a, bisecting the skull. The present study was based on the skull compo nents of the resulting 74 lateral cranial tissue blocks. The tissue bl ocks were radiographed with a Hewleb Packard Faxitron unit. Seven refe rence points were digitized from each film and eight linear dimensions were calculated. Method errors ranged from 0. 12 mm to 0. 52 mm. The dimensions were related to crown-rump length (CRL) and lateral segment developmental stages (LSS). The increases in the linear dimensions of the anterior part of the lateral skull segments were similar to those found previously for the median skull segment. The dimensions of the anterior part of the lateral skull segments were found to increase by 150% during the second trimester, while those of the posterior part in creased by 100% during the same period. Between maturity stages LSS 4 and 5 the dimensions increased by 30-50%, whereas less increase was ob served between stages 5, 6, 7 and 8. This reduction was attributed to the progressive ossification of the cranial base. The almost horizonta l distance from the mandibular condyle (condylion) to the anterior tym panic ring did not change significantly during the second trimester. C omparison of the bilateral skull segments showed no systematic asymmet ry, but a significant individual biological variability in symmetry wi th standard deviations of 0.7-1.8 mm was found.