The other case is even more interesting, be cause it exhibits a cure of aneurism after operation in a manner that has not been de scribed, the principle of which it is not easy to understand. A man was operated on by Mr. Collis, in the Meath Hospital for popliteal aneurism on the 22d of January, 1831. The ligature came away on the seventeenth day, the tumour diminished ; in short, every thing went on well and the patient left the hospital per fectly cured. So far as the aneurism was con cerned, he remained healthy and free from inconvenience until his death, which hap pened in March 1835, from fever, and such an opportunity for pathological inquiry was not neglected. The tumour which had been origi nally of the size of a turkey's egg, was found to have diminished to little more than that of a walnut : externally it felt hard and as if com pletely solidified : on being cut into, however, neither artery nor sac was obliterated, the latter being occupied by a coagulum of a deep red colour, through the centre of which was a canal of a sufficient size to allow the blood from the portion of the artery above the tumour to flow freely into that below it. It seemed as if the current of blood through the sac had never been interrupted, the only effect of the former ligature having been the removal of the im pulse of the heart from it. This aneurism appeared to have been a true one, so far as the. fibrous and cellular coats were concerned, but the fact could not be so satisfactorily demon strated as to admit of no dispute ; however, the absence of the lining membrane and its sharp and abrupt terminations at the healthy portions of the vessel were sufficiently ob vious.
If it be difficult to demonstrate the nature and constitution of the small and recent aneu rism, it becomes impossible when the tumour has attained to a considerable size. It seems probable, however, that the arterial structures will not long endure this state of unnatural distension, and they either ulcerate or tear in their internal and middle coats. A mixed aneurism will thus be formed, having its sac at first composed of all the structures of the artery, and subsequently in the largest portion of its circumference, of the cellular coat alone. The long continuance and gradual increase of some aneurisms, as contrasted with their sudden and rapid growth afterwards, have been explained on this supposition.
Diffused anC2triS771.—An aneurism is termed diffused when the blood, removed from the circulation, is not confined within a pouch or sac, and therefore passes in every direction throughout the cellular tissue of the limb. This may be occasioned by the rupture or ulceration of an aneurismal sac, but far more frequently by some violence applied to the artery itself in such a manner as to open its cellular as well as its other coats. Thus a spicula of a fractured bone, or a pointed sequestrum, in coining from a necrosed limb, may produce the disease ; but the most common examples that fall under a surgeon's observation are furnished by awkward or ignorant persons in their at tempts to perform the operation of phlebotomy.
In the latter case there is an external wound communicating with the injured vessel, and then it also presents a familiar illustration of traumatic aneurism.
When the blood is thus diffused throughout the cellular tissue, there is always the greatest danger; not so much from the loss of a large quantity to the circulation as from the rapidity with which a limb so circumstanced runs into a gangrene,—a rapidity so great that the mor tification either is not or seems not to be pre ceded by inflammation, and its occurrence is often the first notice a surgeon receives of the extent and nature of the accident. When the injured artery lies deep and is covered by a dense and resisting fascia (as in the instance of the posterior tibial artery being ruptured by a blow), it may bleed for some time without affording any indication beyond the pain and tension complained of by the patient, and a slight tumefaction of the limb. When, how ever, the fascia has yielded or sloughed and per mitted a more extended diffusion of the blood, the part becomes swollen, glassy, and oedema tous, pale if the blood did not occupy the cellular tissue underneath, but of a livid colour, like that of a bruise, if it does. The joints in the neighbourhood are kept flexed, and any attempt at motion gives intolerable pain. In a very short space of time circumscribed spots of gangrene appear, which, on separating, per mit masses of very dark coagula to protrude, accompanied by an oozing, or perhaps, a flow of arterial blood, under which a patient will very soon sink. And it may be, the real nature of the case has not been suspected until this blood has made its appearance. Doubtless, if a diffused aneurism has been occasioned by a wound, the rush of blood at the moment, its colour, and the difficulty of controlling the hw morrhage will point out what has happened ; or if there had been a circumscribed aneurism that on a sudden lost its defined character while the limb began to enlarge above and below it, there would be good grounds for suspicion; but in any other case it is so difficult to sepa rate the pain and tension and the other symp toms from those which might naturally super vene on a severe injury, that the appearance of a tendency to gangrene is too often the first circumstance to create alarm. There are many symptoms in which the diffused aneurism differs from the circumscribed, that render the diagnosis of the former particularly diffi cult. It has been already stated that the " bruit de soufflet" is, even when present, not a pathognomonic symptom, and if the vessel lies deep it is not to be heard at all. Pulsation of the tumour, the most satisfactory symptom of an aneurism, is generally absent, and when otherwise, is very weak, fluctuating, and indis tinct. To those who reflect that the effused blood is thrown out amongst inelastic and unresisting structures, that no portion of it is returned to the circulation, but that it lies a coagulated mass amongst the surrounding cellular tissue, the absence of these symptoms will not require explanation.