ABSTRACT
Introduction: The thymus is a primary lymphoid organ. It is a bilobed structure divided into lobules by theconnective tissue septa. Each lobule consists of a cortex and medulla. Most of the studies regarding early foetalhistology of this organ are animal based. The present study has been undertaken to highlight some featuresregarding histogenesis of human foetal thymus.Materials and Methods: In the present study, 30 normal human stillborn/aborted foetuses were studied. Theobtained foetuses were fixed in 10% formalin. After proper fixation they were subjected to dissection. Theobtained specimens were processed by standard paraffin block making procedure. Sections were taken andstained with haematoxylin & eosin. The stained sections were examined under light microscopy using 10x and40x optical magnifications and photographs taken.Results: At 12th week, capsule was thin and cortico-medullary differentiation not much prominent. Epithelialcells and lymphocytes were present. Hassall’s corpuscles were very small and immature. Distinct lobulation wasseen at 18th week with well differentiated cortex and medulla. The gland became more distinct from 21stweekonwards with increased number of Hassall’s corpuscles of various types. 29 week onwards the thymus glandrevealed an adult histological picture.Conclusion: All structural changes viz cortico-medullary differentiation, lobulation and maturity of Hassall’scorpuscles occurred within the first 18 weeks of gestation.