Stereological estimation of total cell numbers in the young human utricular macula

Abstract Conclusion: There is no change in the total cell population and hair cell:supporting cell ratio in the human utricular macula from gestational week 16 and onwards, whereas the lower hair cell:supporting cell ratio and lower total number of cells in the youngest specimens indicate that the utricle is still differentiating and adding new cells at the 10th to 12th gestational week. Objectives: Archival temporal bones were investigated to quantify cell numbers in the utricular macula in fetuses and children. Methods: The age of the subjects ranged from gestational week 10 to 15 years. The optical fractionator was used to estimate the total number of cells in the utricular macula. Results: The total cell number was found to be 143 000 in subjects older than gestational week 16. The number of hair cells and supporting cells did not change between the 16th gestational week and 15 years and was 36 000 and 107 000, respectively. In the youngest specimen (10th and 12th gestational week) there was a statistically significant lower total number of cells (62 000) and a lower hair cell:supporting cell ratio, resulting in a mean number of 13 000 hair cells and 49 000 supporting cells.