European Journal of Cardiovascular Medicine

The thymus is the lymphoid organ of greatest importance. It has structurally separated lobules through the connective tissue septa. That lobule has a cortex and a medulla in it. Many studies of this organ related to the histology of early fetuses are focused on animals. The present study focuses on certain histological features relating to the histogenesis of the thymus in adolescent and fetuses. The thymus is a powerful lymphoid organ and a main immune system regulator, and is responsible for the body’s mobile immunity. The bilobed shape, divided into lobules via connective tissue septa. Every lobule is composed of cortex and medulla.  Materials and methods: The present study has been undertaken on thymus specimens of 25 fetuses of different age groups starting from the crown - rump length (CRL) of these fetuses have been to challenge to morphometry and histometry. The fetuses have been obtained from the Department of Anatomy, Siddhartha Medical College (Govt), Vijayawada over a period of 6 years and one specimen of thymus gland of the age of 15 years taken from the branch of forensic medicine. The fetuses had been tested for their respective crown rump lengths, gestational age and weights were used for the study. They had been constant in 10% formalin for 10 days after which subjected to dissection. Result: The histometric analysis of parenchyma (cortex and medulla) and connective tissue indicates that there was no significant variation in their ratio. The corpuscles frequently seen in thymuses of the early gestational period are called as Solid Hassall Corpuscles (SHC) and were located at the periphery of the medulla within the age group of the present study. Their size ranged from 25-35 μm with a mean of 33.171 μm. Certain corpuscles had a homogenous hyalinized eosinophilic mass in the center encircled by well defined, compactly packed concentric layers of epithelial cells which formed a capsule like structure. This epithelial capsule was separated from the central mass by a subcapsular space that gave a cyst like appearance hence named primary cystic Hassall’s corpuscle (CHC I). Conclusion: The findings of the present study are in conformity with studies related to the volume and size of the thymus with respect to gestational ages as well as with previously mentioned histological features. However, the present study noted different types of HC which are reported in the adult thymus. Hence the period of gestation between 15 and 18 weeks is critical for the development of fetal thymus.