Histomorphometric and developmental analysis of human fetal caecum and appendix with its embryological significance.

Purpose: The variable positions of the appendix can mislead surgeons and physicians to a wrong diagnosis. When appendicitis happens in subhepatic caecum, it can be misdiagnosed and can lead to severe complications during surgical procedures. Therefore, this study aimed to understand the histomorphometric development of the appendix and caecum and to identify when lymphoid follicles appear in the appendix during fetal life.

Methods: The study was conducted on a total of 50 fetuses. The caecum and appendix were carefully dissected. Their position and various measurements were observed. Afterwards, the appendix was taken out for histological processing. All three layers, mucosa, submucosa, and muscularis externa were measured using Image Analyzer Software Image Pro Premiere 9.1, and the appearance of lymphoid follicles was also examined. Results were analyzed using SPSS statistical software.

Results: During the 1st, 2nd, and 3rd trimesters the most common caecum type was type 1: as a lengthy tube, type 3: The lateral wall expanded more, thus it has an asymmetric saccule, and type 4: adult-like caecum. The caecum was mostly situated in the right lumbar region in the 2nd and 3rd trimesters. In the 1st trimester, it was subhepatic in position. The most common position of the appendix was 11 o'clock in 1st and 3rd trimesters. 2nd trimester's most common position of the appendix was 12 o'clock. The thickness of the mucosa, submucosa, and the muscularis externa increases as the trimester increases. The lymphoid follicles have appeared during the 2nd trimester.

Conclusion: The knowledge from this study will be useful in the diagnosis and treatment of malformations, pathology, and anomalies of the caecum and appendix due to congenital causes.