SOME ASPECTS OF EARLY DEVELOPMENT OF THE THYMUS: EMBRYOLOGICAL BASIS FOR ECTOPIC THYMUS AND THYMOPHARYNGEAL DUCT CYST. Algunas observaciones acerca del temprano desarrollo del timo: bases embriológicas del timo ectópico y del quiste del conducto timofar


  • Ivan Varga Institute of Histology and Embryology, Faculty of Medicine, Comenius University in Bratislava, Bratislava University Centrum of Reproductive Medicine of the 1st Department of Gynecology and Obstetrics, University Hospital, Bratislava
  • Paulina Galfiova Institute of Histology and Embryology, Faculty of Medicine, Comenius University in Bratislava, Bratislava University Centrum of Reproductive Medicine of the 1st Department of Gynecology and Obstetrics, University Hospital, Bratislava
  • Veronika Jablonska-Mestanova Institute of Anthropology, Faculty of Natural Sciences, Comenius University in Bratislava, Bratislava,
  • Stefan Polak Institute of Histology and Embryology, Faculty of Medicine, Comenius University in Bratislava, Bratislava University Centrum of Reproductive Medicine of the 1st Department of Gynecology and Obstetrics, University Hospital, Bratislava
  • Marian Adamkov Institute of Histology and Embryology, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Martin


Palabras clave:

thymus, pharyngeal pouches, ectopic thymus, thymopharyngeal duct, timo, foco faríngeo, ectopía tímica, conducto timofaríngeo


Introducción. El objetivo principal de nuestro trabajo es el estudio histológico del desarrollo del timo humano entre la 5ª y la 8ª semana de gestación. Describimos varios términos embriológicos poco usados como: timo secundus, descensus thymi (la base embriológica para situar el timo en la garganta), ductus timicus (la base embriológica para el defecto innato llamado conducto timofaríngeo con posibilidad de formar un quiste). Material y método. Nuestras observaciones se basan en la investigación de 18 embriones humanos entre la 6ª y la 8ª semana de gestación. Resultados. La base del timo es común con la base de las glándulas paratiroideas. Es comparable con las bolsas faríngeas (saccus pharyngeus) en los embriones largos de 8 a 9 mm. La proliferación endodermal del epitelio en el tercer foco faríngeo (focus faringeus 3) es muy visible. La parte craneal y la parte dorsal son la base de origen de las glándulas paratiroideas inferiores. La parte caudal y la parte ventral son la base para el timo. Hemos observado también la notable proliferación del epitelio en la segunda bolsa faríngea, llamado por algunos autores Timo secundus. En nuestra opinión, en el ser humano no se forma un timo funcional en este lugar y la proliferación del epitelio en la mayoría de los casos, se detiene pronto. Conclusión. En este trabajo ofrecemos una vista general sobre la importancia clínica del desarrollo del timo y la descripción de los defectos innatos más frecuentes del mismo.


Introduction. The aim of our morphological study is to describe the development of human thymus from 5th up to 8th week after fertilization in the context of its phylogenesis. We explicate some of the “forgotten” embryological terms with respect to their functions in thymic development, such as “thymus secundus”, “descensus thymi” (an embryological basis for cervical thymus) and “ductus thymicus” (an embryologic basis for a congenital anomaly called thymopharyngeal duct with possible thymic cyst). Material and methods. Our findings are based on the study of 18 human embryos from 6th to 8th week of development. Results. The first primordia of the thymus and parathyroid glands within the endoderm of pharyngeal pouches can be seen in 8 to 9 mm crown-to-rump-length stages. The most evident epithelial proliferation is visible in the paired third pharyngeal pouch (saccus pharyngeus tertius): the cranial dorsal part of pharyngeal pouch initiates the inferior parathyroid gland and the caudal ventral part of the pouch gives rise to the epithelial thymus. We found an obvious endodermal epithelial proliferation also in the second pharyngeal pouch. Some authors depict this proliferation as “thymus secundus”, but the proliferation of endoderm close down and the functional second thymus does not develop in human embryos. Conclusion. In our work we also review the clinical significance of early thymus development, as well as the most common developmental anomalies of thymus.


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