PATHOLOGY.—In 1789 attention was first called to a peculiar constriction of the thoracic aorta at the insertion of the ductus arteriosus Botalli. Careful search for this lesion since that date has discovered a series of cases, so that in 1878, Kriegk was able to report 55 instances of it. This constriction is a definite, locally circumscribed lesion, always limited to the same region, and is entirely independent of all other affections of the aorta, although it may itself be the cause of atheroma and aneurism. Beyond the locality specified stenosis of the aorta is an extremely rare affection, except as the result of outside pressure or of local arteritis. Kriegk says he found only two cases of stenosis of other parts of the aorta, although he searched through forty years of medical literature. A few instances of complete obliteration of the aorta have been recorded, and some instances of universal narrowing of the aorta from congenital obstruction in the heart are given.
The constriction at the ductus Botalli is a congenital lesion, and consists of a sinking in of the superior wall of the aorta just at the insertion of the ductus arteriosus or a little above or a little below the same. This sinking may extend to and involve the origin of the left subclavian artery, but this is not usual. The lower wall of the aorta rarely exhibits any depression.
The ascending and transverse portions of the aorta, together with the main branches, become very much enlarged. As the aorta approaches the constriction, its dilatation does not terminate abruptly, but the vessel tapers down to the stenosed section in a funnel shape. Beyond the stricture the descending aorta may recover its normal size or may remain smaller than natural.
In many cases the aorta, barring the stenosis, is perfectly healthy, but the increased pressure behind the obstruction tends to develop atheroma, aneurism, hypertrophy of the heart, and rupture.
Naturally, the lower part of the body must be deprived of a portion of its quota of blood except for the compensatory circulation which develops. This collateral supply may be so complete that the person affected is unconscious of any circulatory deficiency, and may live an active life to old age. An Austrian officer born with this lesion was able to serve in all the campaigns from 1790 to 1815, and then died one day sitting at a card-table. Another man lived ninety-two years with his aorta constricted. The collateral communication between the upper and lower segments of the aorta is established by means of the deep arteries of the neck, the transversus colli, the dorsalis scapulæ, the subscapularis, the intercostals, and the lumbar arteries. The internal mammary also communicates directly with the epigastric artery. These vessels become enormously dilated, so that the superior intercostal, for instance, may equal the femoral in size.
| FIG. 52. |
| A, Appearance of Aortic Arch in Early Foetal Life.—B, Stenosis of the Aorta. |
ETIOLOGY.—The lesion is a congenital one, and results from a defective development of the aorta. In early foetal life the descending aorta is a continuation of the ductus Botalli, and the aortic arch looks like an independent communicating vessel. (See fig. 52, A.) As the arch develops, however, it gradually forms a more direct union with the descending portion, until finally the longitudinal axes of the two parts form one uniform curve and the ductus Botalli becomes a side branch. At birth there is physiologically a slight nicking of the upper wall of the aorta at the point where the two sections are joined, and the stricture we are studying seems to be merely an exaggeration of this physiological mark. Just how the depression becomes established is not clear and the explanations given are not satisfactory.
SYMPTOMS.—Indications of this lesion are usually very obscure or absent, and it is only discovered at the autopsy. Severe headache is sometimes complained of, and dyspnoea, cough, hæmoptysis, and vertigo may occur if the stenosis is excessive.
Physical Signs.—One of the most marked signs is the conspicuous beating of the dilated arteries around the shoulders and ribs. These arteries may be seen and felt. If the patient is very fleshy, however, they may be concealed. There is usually a marked contrast between the arteries of the upper and lower extremities. The former are full and strong, while the latter are weak and barely perceptible. In many cases it is almost impossible to feel any pulse in the abdominal aorta or in the crural arteries. A loud murmur is also described as occurring over the aorta. This murmur is post-systolic, and does not correspond to any of the ordinary aortic murmurs.