Talk:Paper - Persistent thyroglossal duct in a rabbit (1934)

PERSISTENT THYROGLOSSAL DUCT IN A RABBIT

By R. K. PAL

Department of Physiology, Prince of Wales Medical College, Patna, India

In the course of dissection of the neck of an adult female rabbit for the purpose of examining any structural changes which may have occurred in the thyroid after splenectomy, a very fine cord-like structure was found connected with the left lobe of the thyroid gland running for about a centimetre and a half in front of the cricoid and thyroid cartilages behind the hyoid bone. The whole thyroid gland with the cord-like structure attached to it was removed and sections were cut in series and stained with haematoxylin and eosin.

Under the microscope, the section of the cord-like structure revealed an irregular lumen, lined by columnar epithelium. The convolutions of the lining epithelium have produced gland-like depressions and enclosed areas which look like vesicles. The outermost coat was composed of fibrous tissue, and the intermediate one exhibited both fibrous and unstriped muscular tissue (fig. 1).

As the cord approached the thyroid gland the lumen became smaller and smaller and the vesicles in the internal coat increased in number and the external coat with the unstriated muscle fibres was found to be thinner too. None of these vesicles contained colloid material. Some accessory or aberrant thyroid bodies (as first described by Zuckerkandl in 1879). were found in the course of the duct in the neighbourhood of the left lateral lobe of the thyroid. Each aberrant mass with a thin connective tissue capsule consisted of vesicles lined by short columnar and cubical epithelium, without colloid, which are quite different from those of the adjoining thyroid gland (fig. 2). Fig. 3 shows the histological structure of one such aberrant mass, under a higher magnification.

The structure of the thyroid gland in the vicinity showed the presence of stored-up colloid material in the vesicles (by Hewers’ method (3) of differential staining by (a) haematoxylin and congo-red and (5) methyl blue and orange G).

Since the finding of this cord-like structure the neck region of about twenty other experimental animals was dissected with the utmost care, but the same structure was found in none of them.

DISCUSSION

The thyroid is originally developed as a tubular duct which bifurcates and subsequently divides into a series of cellular cords from which the isthmus and ~ the lateral lobes of the thyroid gland are developed. The presence of a cord in this situation connected with the thyroid gland, its internal coat lined by 23—2

Fig. 1. Thyroglossal duct (under low power).

Fig. 2. Part of a thyroid lobe and an aberrant thyroid mass to show the difference in,structure.

Persistent Thyroglossal Duct in a Rabbit

355 356 R. K. Pal

columnar epithelium with presence of vesicles as enclosures within its convolutions and external fibrous coat containing unstriped muscular fibres, all _

Fig. 3. Structure of an aberrant thyroid mass (in the neighbourhood of the duct).

suggest that the structure was a persistent thyroglossal duct. The presence of thyroid-like glandular masses in the course of the duct adds to the probability (4).

SUMMARY

The structure of a persistent thyroglossal duct in a rabbit is described. The most interesting feature of the observation is the continued differentiation of the thyroglossal duct until it resembles the alimentary tract with convoluted epithelium, tubular glands in the submucosa, internal and external muscular coats and the most external fibrous tunic.

I wish to express my thanks to Mr Hyder Ali Khan, F.R.C.S.E., Professor of Anatomy, Medical College, Patna, for kindly taking the micro-photographs, and Mr H. Banerji, of the department of Physiology, for assisting me in staining the sections.

REFERENCES

(1) Fraszer, J. E. (1931). Manual of Embryology, p. 239.

(2) Normentafeln Entwicklungsgeschichte der wirbelthiere, Tables 10.24. (3) Hewer, E. (1927). J. Path. Bact. vol. xxx.

(4) Jorpan, H. E. (1924). A text book of Histology, 3rd edition, p. 564.