When in consequence of arteritis, or from any other cause, the elasticity of the arterial structure becomes impaired or weakened, a dilatation of the vessel at the spot so debilitated ought to be the result ; and this probably takes place in all arteries previous to the formation of idiopathic aneurism. But the circumstances that determine an artery to become dilated rather than to ulcerate are very obscure, for the same morbid appearances in the vessel are observed to precede both. In the eleventh number of the Dublin Journal of Medical Science there is an account of two cases of internal aneurism, one formed by ulceration of the internal and middle coats of the artery, which burst into the oesophagus ; the other, evidently by dilatation, which destroyed the patient by pressure on the trachea : and in both the aorta exhibited the same appearances of inflammation and steatomatous deposit be neath the lining membrane. The preparations are preserved in the collection of the school in Park-street, and as showing this pathological fact are extremely satisfactory. Again, it is not easy to say what dilatations should be con sidered aneurismal or not. The aorta, in a great proportion of subjects above the age of forty, is dilated ; yet such dilatation is not regarded as an aneurism. Other arteries present a similar appearance occasionally ; and a case occurred not very long since in the Meath Hospital, in which all the arteries of the inferior extremities in an aged man were dilated to more than twice their natural calibre. These vessels were found after death filled with coagulated blood, yet as the fluid seemed to circulate through them during life, and the patient never ex perienced any inconvenience, it is difficult to admit them as specimens of true aneurism. On the other hand, nearly at the same time, a man died in another hospital who for years had a small aneurism of the femoral artery, with every observable symptom of the disease except that the growth of the tumour was un usually slow ; and on dissection this appeared to have been a species of true aneurism, caused by an equal dilatation of the entire circum ference of the vessel, and did not contain coa gulated blood. It would seem, then, impos sible to pronounce during life on the real nature of an aneurismal tumour, nor is it always easy to demonstrate it after death.
In most instances of aneurism, particularly those of long standing, the edges of the aperture into the sac are smooth and even, and the lining membrane seems to be prolonged into it. The internal wall of the sac is so thickened, and all the parts so matted together and confused by depositions of lymph and fibrine, that the appearances altogether become so deceptive as almost to countenance the old opinion as to the pathology of the disease. Professor Scarpa, who principally opposed the doctrine of aneu rim. by dilatation, was obliged to support his opinions more by argument than by facts de monstrable by dissection ; and although later in vestigations, particularly those of Mr. Hodgson and Air. Guthrie, have satisfactorily proved the occasional existence of both true and false aneurism, yet it must be a favourable case and patient examination that will enable the morbid anatomist to exhibit its nature and structure without possibility of error. When cases of inflamed or diseased artery are seen, compli cated with aneurism, and the same depositions are observed in the artery and in the sac, it proves beyond doubt the identity of structure in both. Thus, if an aorta be found studded
over with specks of a soft steatomatous deposit situated between its internal and middle coats, and if on one side of it an aneurism is placed, in the sac of which, throughout its entire ex tent, the same appearances and the same de posit are observed, it follows that the same structures must exist in both, and that one is a prolongation of the other. One of the cases already noticed as being a true aneurism, that destroyed the patient by pressure on the trachea, exhibited such evidence of its nature : and a similar one, but still more satisfactory, occurred in the person of a gentleman, who died some years since. This patient had laboured under some anomalous cerebral symptoms, and on inspecting the brain a small aneurismal tumour was seen at the bifurcation of the basilar artery, in the sac of which were found the same kind of earthy depositions that pervaded all the arteries of the body—the same so generally observed in the arteries of aged persons. These examples are sufficient to prove that aneurism by dilatation may exist, and perhaps its occur rence in the aorta and larger vessels is more frequent than has been supposed.
During the past spring two opportunities occurred of examining into the nature and condition of aneurism, both in its early stage and long after it had been apparently cured by operation. They were, probably, both ex amples of what has been termed true aneu rism, although unquestionably all the coats of the artery were not engaged : and as the mor bid appearances have not been hitherto de scribed, it may be useful to take notice of them here.
A man was admitted into the Meath IIos pital, with popliteal aneurism in each ham : one of these had existed for several weeks ; the other was of very recent occurrence. The limb in which the older and larger one was situated was first made the subject of opera tion, the femoral artery was tied, but the patient died on the sixteenth day afterwards, of venous inflammation, the ligature on the vessel still remaining firm and undetached. On examining the aneurismal tumour exter nally it appeared of an oval shape, and to have been formed by the gradual expansion of all the coats of the vessel. On being cut into, however, it was found that the lining mem brane was wanting throughout the entire extent of the sac, the edge of it terminating sharply and abruptly, above and below, at the junc tions of the tumour with the more healthy parts of the vessel, and being as accurately defined as if made by a careful dissection. The fibrous coat was evidently continued into the tumour, which seemed to be formed of an expansion of it and the cellular. It was, moreover, otherwise diseased, being thickened, greatly softened and thrown into irregular rugze or folds, the interstices between which were filled with coagula of lymph or fibrine. As the sac of this aneurism was in a state of sup puration, the deficiency of the lining mem brane was attributed to that circumstance until the other aneurism came to be examined when the same appearances were observed. The second tumour was not so large as a walnut and evidently formed by the gradual expan sion of the fibrous coat, for the abrupt ter minations of the lining membrane at the healthy extremities of the artery were still more exactly defined.