Bibliogr. s. e305-e306

Purpose: The aim of the study was to develop the normative values of linear indices to the diagnosis of changes in size of the subarachnoid space. Material and methods: Retrospective studies were conducted based on 507 head computed tomography (CT) examinations in children from 0-18 years of age. In total 381 tests were selected for correct reference values. Patients were divided into age groups. For each group, linear indices were calculated, taking into account the size of the fluid spaces in relation to the size of the skull and then the mean with standard deviation, median, as well as 10th and 90th percentile were calculated. The range between the 10th and the 90th percentiles was defined as the reference value. Results: Obtained normative values, minimum and maximum for all groups: index of basal cistern size to the size of the skull - 0.129-0.197; index of basal cistern transverse dimension to the size of the skull - 0.173-0.255; index of basal cistern sagittal dimension to the size of the skull - 0.086-0.150; index of prepontine cistern - 0.034-0.067; index of interhemispheric fissure width - 0.044-0.127; index of Sylvian fissure - 0.036-0.085; index of insular cistern width - 0.020-0.074; index of subarachnoid space - 0.017-0.081. Conclusions: The linear indices can be calculated based on images achieved during routine CT examination. The reference values allow us to determine if the size of the subarachnoid space is within the normal range for a given age group. The results from the oldest age group can also be referred to the adults. Key words: external hydrocephalus, subarachnoid space, computed tomography (CT), linear indices, infants and children.