Paper - Three examples of a right aortic arch
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Three Examples of a Right Aortic Arch
By Douglas G. Reid, M.B., Ch.B. Edin., B.A. Trin. Coll. Camb.,
Demonstrator of Anatomy in the University of Cambridge.
Cases in which there is persistence of the fourth right aortic arch are, of course, very well known.
Nevertheless, in the cases here recorded, which occurred in adults, presented no fibrous remnants of a left aortic arch, and were not associated with transposition of the viscera or any marked cardiac anomalies, there are certain points which appear worthy of note.
Unfortunately, a number of structures had been cut before I saw the specimens.
In Cases II. and III. (see figs. 2, 3) the aortic arch, as it passes backwards on the right side of the trachea, lies just above the right bronchus.
In Case I., however, it is placed at a considerable distance above the bronchus (see fig. 1). In this specimen the highest point of the arch lies 1 cm. below the upper border of the body of the first dorsal vertebra.
The aorta ascends through the superior aperture of the thorax into the root of the neck, and must have given rise to marked suprasternal pulsation.
But in Case I., as in Case III., and as in most cases of right aortic arch (Allen Thomson and Turner), the left subclavian artery arises posteriorly,
and the left common carotid is the first branch of the arch (see figs. 1, 3).
In Case I. it arises in front and to the right of the trachea, is still anterior to this at the level of the presternal notch, and must also have given rise to marked pulsation in this situation.
It is noteworthy, therefore, that suprasternal pulsation, even when most marked, may not always indicate the presence of an aneurism, and other physical signs may help to show this.
However, it seems worth while revising the causes to which attention has now been drawn, apart from aneurism, of suprasternal pulsation.
(1) An aortic arch which ascends to the level of the presternal notch.
This may or may not be due to the persistence of a more primitive position.
Poirier states that “ il n’est pas rare chez les sujets agés de voir la crosse
de l’aorta battre dans la dépression sus-sternale—en raison du développement du grand sinus.” (2) Abnormally situated branches of the aortic arch.
(a) A right (or left) innominate artery 1 “may divide higher than usual, and may then incline abnormally to the left, mounting in front of the trachea above the sternum” (Morris’s Anatomy).
(b) The right subclavian, when its place of origin is to the left of the middle line (Hutchison and Rainy, Clinical Methods).
(e) The left common carotid in certain cases of right aortic arch, as I have indicated. ‘
(3) The thyroidea ima, whose pulsations one sometimes sees as well as feels.
In Case I. the pulmonary artery, 2 inches long, lies in its usual situation, and divides, as normally, a little below, in front of and to the left of the bifurcation of the trachea, and in front of the root of the left bronchus
(a relation never mentioned in the books). The serous pericardium had been removed, and one could not determine
the height to which it had ascended?
In Case III., as in the case described by Allen Thomson (Glasgow Medical Journal, vol. xi., April 1863, p. 1), in which both aortic arches apparently had remained patent throughout until a relatively late period of intra-uterine life, and in which there was a left innominate artery, the posterior part of the arch and the upper part of the descending aorta presented a dilated portion. This is placed behind the oesophagus, and corresponds to the pouch-like trunk in Turner’s ordinary case of right aortic arch.3
It sends forward a projection which lies to the left of the trachea, gives origin to the left subclavian artery, and terminates in a truncated extremity to which, at the root of the subclavian (see fig. 3), the ligamentum arteriosum, round which the left recurrent laryngeal nerve hooks, is attached.
Therefore in this specimen the trachea and oesophagus are almost completely encircled by the aorta. Allen Thomson and Turner first pointed out that this dilatation which lies
1 In old people this artery (Poirier) terminates “ plus haut, au niveau du bord supérieur de l’extre'mité sternale de la clavicule.” Annandale demonstrated that the innominate artery may be compressed by a finger introduced behind the upper border of the sternum.
2 Normally the serous sac of pericardium, as Poirier points out, ascends to the back of
the root of the innominate artery, and therefore into the superior mediastinum. The textbooks overlook this important point. The student, when asked the contents of the superior mediastinum, always omits the serous pericardium and the azygos vein (whose arch reaches “ a la hauteur de la 4° ou de 19. 3° vertebre dorsale” (Poirier).
3 British and Foreign Medical Review, 1862, vol. xxx, Three Examples of a Right Aortic Arch 177
behind the oesophagus is to be regarded, not as secondary, but as representing a persistent left aortic root (tge. aportion of the left dorsal aorta caudad to the dorsal extremity of the fourth left aortic arch).
fiG. 2.—Ca se II.
In Case I. the aortic arch itself curves quite distinctly inwards behind the oesophagus. Its posterior part, and the commencement of the descending aorta (Which lies behind the oesophagus) are also somewhat dilated, but there is no distinct projection as in Case III., and the subclavian artery 178 Mr Douglas G. Reid
arises more directly from the arch. The aorta extends distinctly beyond the left margin of the oesophagus, and produces a deep groove on the medial surface of the left lung above the hilum. L
Apparently in association with the unusual height to which the aortic arch ascends, the upper aortic intercostal arteries are much less oblique
fiG. 3. —Case III.
than is usually the case. The descending thoracic aorta (the abdominal aorta had been removed) is remarkably sinuous}
Above,“it lies to the left of the middle line, but, taking a curved course, it comes to lie entirely to the right of the middle line and produces a deep
1 Another case of ri ht aortic arch with persistence of the left aortic root, as in this case, and sinuosity of the escending aorta, is recorded by Annan (Journal of Anatomy and Physiology, vol. xliv. p. 241). As in this case, there was no scoliosis. The presence or absence of atheroma is not noted. Atheroma was present in my specimen, Three Examples of a Right Aortic Arch 179
depression behind the hilum of the right lung. Below this level it regains a position to the left of the middle line, into which it comes near the aortic hiatus of the diaphragm.
In Case II., where there is a left innominate artery (partial persistence of the fourth left aortic arch) and no trace of the left aortic root, the descending aorta as it passes downwards inclines gradually to the left and forwards to reach the middle line close to the hiatus.
Little regard has been taken of the relations of the thoracic duct in c_ases of a fourth right aortic arch, and even Garnier and Villemin, in a recent and detailed description of a right aortic arch in a foetus,‘ omit to mention the duct.
Allen Thomson, however, states that in his case it lay on the right. side of the descending thoracic aorta, between it and the azygos vein, and joined the angle of union of the right jugular and subclavian veins.
But in Case II. the duct, except near the aortic hiatus of the diaphragm, Where it lies behind the aorta, is placed on the left side of the descending aorta in front of the left intercostal arteries. Above, it passes towards the right jugular-subclavian conﬂuence, but unfortunately its upper end had been cut by the dissectors.
In Case III. there is no duct to be found.
In Case II. a portion remains_which lies in front of the left intercostal arteries, behind the parts of the aorta which lie to the left of the middle line, but to the left of the intervening portion opposite its concavity (see fig. 1). “In human embryos the observations on the thoracic duct are still scanty.” ,
In Case III. the fibrous cord (ligamentum arteriosum) which passes from the pulmonary artery to the aortic root, and round which the left recurrent laryngeal nerve hooks, has already been mentioned.
In Case II. there are two fibrous cords. One (see fig. 2, B), a stout band, is attached to the right pulmonary artery 15 mm. from its origin, and passes to the right and upwards to a point on the inferior aspect of the aortic arch. The right recurrent laryngeal nerve (fig. 2, A) takes origin opposite this point, and comes into contact with the right extremity of the band. '
The other arises from the pulmonary trunk, and divides into a number of distinct cords. In Case I., in addition to a stout band, a fine cord is present; and both are attached to the pulmonary artery close to one another.
It was unfortunate that only the parts shown in the figures had been left by the dissectors.
I Biblioyraphie Anatomique, vol. xix. p. 277.
A consideration of the points of attachment of these fibrous remnants of the sixth (pulmonary) arches would indicate that in Case II. a distinct portion of the right pulmonary artery was formed by the sixth right aortic arch, as is normally the case according to Bremer}
The arrangement in Case I. may indicate that the pulmonary arches have fused (a fusion is described by Bremer) up to the points of origin of the pulmonary arteries, and, in view of the very plastic nature of the embryonic arteries, a variation such as this is not surprising.
In Case II. it would appear that the left sixth arch had remained patent until a relatively late period of intra-uterine life.
' In cases of right aortic arch with persistence of the left aortic root (fig. 1) the presence of a fibrous remnant representing the right pulmonary arch has hitherto escaped observation.
It would appear from the presence of two distinct cords in Case I. that both pulmonary arches had remained pervious until a relatively late period, although the left may be the one which usually remains patent until birth.
I am not aware that the presence of the fibrous remnants of both sixth aortic arches has hitherto been recorded.
The relations of the other parts are accurately represented in the figures.
It will be seen that the vena azygos major (vena azygos) does not present its usual direct relation to the trachea, the aortic arch, of course, intervening. The right vagus nerve is also separated from the trachea by the aorta. In cases like III. and I. the recurrent laryngeal nerves come into close relation with the trachea at practically the same level.
In Case II. the vena azygos lies in contact with the posterior aspect of the descending aorta, and takes a course exactly parallel to it. But in Case I. this vein, like the thoracic duct, is not curved in conformity with the aorta.
Although the question as to what inﬂuence the atheroma in Case I. had in producing the sinuosity is to be kept in mind, the occurrence of sinuosity in two cases in which there was a left aortic root along with the right aortic arch suggests that the condition may be of developmental origin.
1 Rathke held that in mammals both pulmonary arteries arose pr-imitively from the sixth left aortic arch.
Bren1er’s recent papers (see the Anat. Record, 1909, vol. iii., No. 6, p. 334) indicate that in man the pulmonary arteries arise, one from the right and the other from the left sixth arch, which, however, never (.3) forms a definite part of the left pulmonary.artery.
His had alrearly stated that priniitively a pulmonary artery arises from each sixth arch, but that later both spring from the sixth left arch.
Turner, from the consideration of a case described by Breschet, also specially pointed out (in 1862) that in man the pulmonary arteries might arise one from each sixth arch.
In such cases, on the other hand, the presence or absence of correlated variations of neighbouring structures is noteworthy. Thus there was no corresponding sinuosity of the thoracic duct, although the duct, of course, is related closely to the aorta during development.
In cases of right aortic arch, that relation of the thoracic duct to which I have drawn attention, viz. its presence on the left side of the descending thoracic aorta, also appears Worthy of special notice, and suggests that primitively there is a more symmetrical arrangement of the lymphatic channels than is at present known to exist.
Cite this page: Hill, M.A. (2019, October 22) Embryology Paper - Three examples of a right aortic arch. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Three_examples_of_a_right_aortic_arch
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