Paper - Thyro-Glossal duct or canal of His (1881)
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Thyro-Glossal Duct or "canal of His"
By C. F. Marswati, M.D., BSc.
House Physician to the Metropolitan Hospital, late Senior House Surgeon to the North-Eastern Hospital for Children, late Platt Physiological Scholar in the Owens College. (PLATE I.)
Having recently had the rare opportunity of making an autopsy on a child in whom there was a so-called persistent “canal of His,” I venture to publish a description of my specimen, in the hope of throwing some light on the morphology of this interesting malformation.
The child in question was a male, five years of age; he was admitted to the North-Eastern Hospital for Children, under Mr Bilton Pollard, for the purpose of having the “canal” excised. He however contracted diphtheria, and died before the operation could be performed. I here take the opportunity of expressing my great obligation to Mr Pollard for his generosity in permitting me to publish the case.
Before describing my specimen, I shall briefly refer to the more important accounts given by previous writers on the subject.
1. Raymond Johnson! describes two cases of “persistent lingual duct” which are typical examples of what is known to surgeons as the “‘canal of His.” In both his cases there was an open sinus in front of the neck discharging mucus; from this a cord was found passing up to the hyoid bone. In both instances the cord had a patent lumen for a short distance; one was lined by stratified epithelium, the other was not. One case was a female, aged 15 years, in whom the sinus had been present for five years; the other was a female aged 6 years, with a sinus of two years’ duration.
2. Concerning the developmental part of the question, His? has shown that the thyroid gland of man develops in three independently arising parts—(1) a median tubular outgrowth from the ventral wall of the pharynx, which forms the isthmus of the thyroid gland and also the lobus pyramidalis, when this exists. (2) Two solid lateral outgrowths which form the lateral lobes of the thyroid. The median portion he terms the thyro-glossal duct, and subdivides it into an upper portion leading from the foramen cecum to the hyoid bone, which he names the lingual duct, and a lower portion, the thyroid duct, extending from the hyoid bone to the isthmus of the thyroid gland. His states that these ducts may persist in whole or in part, but he has never seen a case where the duct was patent for the whole distance from the foramen czecum to the thyroid gland, it being always obliterated where it passes behind the hyoid bone.
1 Lancet, 10th May 1890.
2 Anatomie Menschlicher Embryonen, iii. pp. 97-102, 1885. ner. of Arad Phys. Oct"189). Vol. XX) Journ Anatecé Pays. Oct? 1891. HSVol VE PUL.
See C.F-Marshall del. 4 F Hoth Lith! Edin?
3. In a later paper! His gives further details of the development, and shows that the middle thyroid rudiment bifurcates at its lower end, forming two lateral lobes at right angles to the main duct; these lateral divisions fuse with the lateral thyroid rudiments, and thus form parts of the lateral lobes as well as the isthmus of the thyroid gland.
4. Bland Sutton? describes the processus pyramidalis of the thyroid gland as being part of the original thyro-glossal duct.
Neither His nor Bland Sutton make any mention of the canal and sinus opening in front of the neck, which is known to surgeons as the “canal of His.”
5. An entirely different explanation of the origin of the median canal and sinus is given by Kostanecki and Mielecki® and also by Kanthack.* According to these authors this structure must be regarded as a median fistula caused by deficient closure of the sinus cervicalis., The sinus cervicalis is a deep semicircular groove lying behind the pharyngeal region between the body and head of the embryo, and occupying its lateral and ventral surfaces, It is caused by the anterior visceral arches, especially the hyoid arch, overlapping the posterior ones, and it may be compared to an opercular cavity. Normally it becomes obliterated, but, according to the above writers, in some cases its median portion persists and gives rise to a median fistula.
Kanthack suggests that a complete median fistula may be due to a tear through the closing membrane of the second branchial pouch or groove into the sinus cervicalis. No direct evidence, however, is quoted in support of this suggestion.
Description of Specimen
In the anterior median line of the neck, about one inch above the sternum, was a sinus discharging a small quantity of mucoid fluid. This had been noticed for about a year, and had discharged at irregular intervals, becoming closed up in the intervening periods.
From this opening a hard cord could be felt extending up to the hyoid bone. On dissecting the front of the neck this cord was found to be tubular and patent up to within half an inch of the hyoid bone: the upper end was firmly attached to the hyoid bone, the lower end dilated into a thin-walled sac opening on to the surface at the external sinus. The sac and tube lay between the skin and the anterior layer of deep cervical fascia: at no place was there any connection with the thyroid gland.
1 Archiv fir Anatomie und Entwickelungsgeschichte, 1891, pp. 26-82.
2 Dermoids, pp. 79-83.
3 Virchow’s Archiv, vols. 120, 121.
By dividing the hyoid bone the tube could be traced as an ill-defined fibrous cord on the dorsal surface of the hyoid bone, to which it was closely attached, and passing through the substance of the tongue up to the foramen cecum. About three quarters of an inch from the foramen cecum it again became patent and continued so up to the surface of the tongue. The canal was thus open at both ends but obliterated in the middle part of its length.
On further dissection a lobus pyramidalis was found passing. from the left side of the isthmus of the thyroid to the hyoid bone, the upper end being united to the median fibrous cord at the same place as the above-mentioned canal. In other words, the fibrous cord behind the hyoid bone was continuous both with the pyramidal lobe of the thyroid and with the tube leading to the superficial sinus.
- The above description will be made more clear by reference to the figures (Plate I).
Fig. 1 shows the canal and sac exposed by reflecting the skin from the middle line of the neck.
Fig. 2 shows a dissection of the thyroid gland and under surface of the tongue. The lobus pyramidalis is seen arising from the left side of the thyroid gland; the upper end of the canal is joined by the pyramid, and the two structures are continued onwards as the median fibrous cord, which is exposed by dividing the hyoid bone. Further on the canal is seen to become patent and pass up to the foramen cecum.
Fig. 3 is a slightly diagrammatic view of the parts in question. The tongue and upper canal (lingual duct) are shown in vertical section as far down as the hyoid bone; below the hyoid bone the parts are seen in elevation. The thyro-glossal duct is here shown in its whole length, the shaded portion representing the obliterated part which I have referred to as the fibrous cord. THE THYRO-GLOSSAL DUCT OR “CANAL OF HIS.” 97
Sections of the canal in its middle portion show the following structure. Externally it is composed of very dense fibrous tissue ; internally there is an irregular lumen not enclosed by any definite epithelial layer. The main substance of the canal consists of an irregular arrangement of fibrous tissue, numerous blood-vessels, and masses of cells. The cells vary in size and shape, but the majority are more or less rounded in outline with distinct nuclei. In some places they appear aggregated together in large irregular masses with very little fibrous tissue ; in other places the fibrous tissue is abundant and the cells few in number. The whole structure gives the idea of embryonic or imperfectly developed glandular tissue.
Sections of the pyramid show that it is composed of ordinary thyroid gland tissue.
Sections of the fibrous cord show nothing but fibrous tissue and no trace of any duct.
No direct connection exists between the pyramid and the canal of His at their point of junction with the fibrous cord.
Let us now consider what light these facts throw on the explanation of the origin of the “canal of His” The possible views of the origin of this structure may be reduced to three :—
- That it belongs developmentally to the thyroid gland.
- That it is formed by persistence of part of the sinus cervicalis.
- That it is of independent origin.
It appears to me that all the facts shown in my specimen tend in favour of the first view, the main points being (1) that the canal and the pyramidal lobe are both equally firmly united to the median fibrous cord ; (2) the apparently glandular structure of the canal seen on section; (8) the patent foramen cecum and short canal leading from it representing the lingual duct.
It hence appears a reasonable explanation that the canal of His is the remnant of one of the bifurcations of the original median thyroid rudiment, the other bifurcation forming the pyramidal lobe of the thyroid gland. The imperfectly developed gland tissue of which the canal seems to be composed is strong evidence in favour of this view. This explanation is also supported by the fact that the pyramid, when present, is always attached to one side of the thyroid gland and is not really median. In my case it was attached to the left side: His! figures a case where it is attached to the right side and forms part of a persistent thyro-glossal duct. Professor His has moreover kindly informed me by letter that he has seen a case in which there were two fully developed pyramids, one on each side.
The view that the canal is formed from the sinus cervicalis can I think only be regarded as a suggestion, and has at present no direct evidence to support it. Moreover, the history of these cases is strong evidence against this view. In Mr Raymond Johnson’s cases and in my case the sinus was not noticed till the child was several years old: now, on the supposition that they are congenital fistule, we should expect them to be most marked, or at any rate present, at birth.
Again, the account given by Kanthack of the sinus cervicalis bursting through into one of the branchial clefts is without parallel in embryology, and can hardly claim serious consideration until direct evidence in support of it is forthcoming.
Against the view of independent origin is the presence of the deep foramen caecum, the presence of a pyramid to the thyroid, and other facts mentioned above, all showing that the thyroid gland had in this case developed in an exceptional manner.
In the absence of evidence to show whether a pyramid to the thyroid gland is always present in these cases, it is impossible to come to a definite conclusion, but I think that the facts shown by my specimen tend in favour of the view that the socalled “canal of His” is a remnant of the middle thyroid rudiment of His. It is not difficult to imagine that this may gradually become dilated at its lower end into a sac by the secretion of mucus from the wall of the canal, and that this sac ultimately causes the skin to give way by its pressure till a sinus is formed.
1 Anatomie Menschlicher Embryonen, iii. p. 100, fig. 67.
If this explanation is correct it is easy to see that a persistent thyro-glossal duct may be due to the persistence of either of the two lobes formed by the bifurcation of the median thyroid rudiment. In the case described by His! it is the right lobe or pyramid of the thyroid, which forms the lower part of the thyro-glossal duct, the left lobe of the thyroid rudiment having become obliterated in his case. In my case both bifurcations had persisted, the one as a pyramid, the other as the “canal of His.”
In conclusion, I must express my thanks to my brother, Professor Milnes Marshall, for much help in connection with the embryological bearings of the subject. My thanks are also due to Professor His and Mr Bland Sutton.
Explanation of Plate I
(All the figures are natural size.) —
Fig. 1. Canal of His exposed by dissecting the skin from the median line of the neck. c¢, canal; 2, hyoid bone; s, sac with open sinus.
Fig. 2. Dissection of the thyro-glossal duct, thyroid gland, and base of the tongue. , upper end of canal of His; f, fibrous cord; A, hyoid bone; J, lingual duct opened and fixed by pins; m, muscles cut through at base of tongue; p, pyramidal lobe; z, thyroid cartilage; ¢h, thyroid gland ; tr, trachea. ; ;
Fig. 3. Semi-diagrammatic figure: the upper parts are in vertical section, the lower part in elevation; /f. c, foramen cecum; s, sac with sinus opening in front of neck ; other letters as before,
1 Loc, cit., fig. 67.
Cite this page: Hill, M.A. (2021, June 24) Embryology Paper - Thyro-Glossal duct or canal of His (1881). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Thyro-Glossal_duct_or_canal_of_His_(1881)
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