Structural and ontogenetic study of the urachus in human fetuses.

The objective of this work was to conduct an ontogenetic and structural study of the urachus. We studied 40 human fetuses (13-20 weeks post conception, WPC). The urachus was stained in Masson's trichrome, to quantify connective tissue and smooth muscle and to determine the urachal lumen area. Weigert's resorcin-fuchsin was used to observe elastic fibers, and picrosirius red and immunohistochemistry analysis were used to observe collagen. The images were captured with Olympus BX51 microscopy and an Olympus DP70 camera. The stereological analysis was done using the software Image Pro and Image J, to determine volumetric densities. For biochemical analysis, the collagen concentrations were expressed per milligram of dry tissue. Means were compared using the unpaired t test (p < 0.05). Quantitative analysis documented a statistically insignificant increase (p = 0.1475) in volumetric densities of smooth muscle in the urachus of males (23.02%), when compared with females (18.43%), and a statistically significant increase (p = 0.0439) in volumetric densities of connective tissue in the urachus of females, (67.64%) when compared with males (58.38%). Total collagen concentrations in the male (31,919-56.792 microg/mg, mean 45,656) and female fetuses (33,485-48,527 microg/mg, mean 42,308) did not differ significantly (p = 0.5912). At higher gestational ages, the urachal lumen area was smaller. In 13th WPC fetuses, the urachal lumen area was 16,301 microm(2) and in 17th WPC fetuses, the urachal lumen area was 1,676 microm(2). We determined that the urachal lumen was closed from the 17th WPC in all fetuses.