Morphological Study of Foetal Thymus: A Cross-sectional Study

Abstract

Introduction: Thymus is a primary central lymphoid organ and a key regulator of the immune system. It develops from the ventral aspect of the 3rd pharyngeal pouch and also gets contribution from the 4th pharyngeal pouch. It migrates caudally into thorax due to its attachment to the pericardium and the aortic sac. Aim: To determine the morphometry of thymus gland in human foetuses. Materials and Methods: It was a cross-sectional study which included 33 human foetuses available in the Department of Anatomy, Sri Aurobindo Medical College and Postgraduate Institute (SAMC and PGI), Indore, Madhya Pradesh, India, over a period of three years. The samples were divided into four groups as per the Gestational Age (GA), (13-16, 17-20, 21-24, 25-29 weeks), based on measuring the Crown Rump (CR) length. After making a midline incision extending from the neck to the chest wall, the thoracic and cervical part of the thymus were displayed and its height and width were measured. For statistical analysis Statistical Package for the Social Sciences (SPSS), version 20.0 was used to analyse the association between the present findings in the given study groups. Results: Cervical extension showed great variability in different groups. It was either bilateral (16), unilateral (9) or even absent (8) in some cases. Cervical extension showed variable appearances like, coiled, lobulated or cord-like. In four cases, it reached upto the lower pole of thyroid. The shape of the thoracic part of the thymus was either vertically elongated or curved, lobulated or retort shape. Conclusion: The present findings of morphometry of foetal thymus are important for radiologists to differentiate thymus from other mediastinal structures and for surgeons during thymectomy. With increasing foetal age, there is regression in the cervical part of the thymus.