There are certain lesions to which the name aneurysm is commonly given, but which do not accord with the description given above.
Cirsoid Aneurysm And The Aneurysm By Anastomosis are somewhat allied forms. The Cirsoid aneurysm is sometimes called varix arterialis, and the name is suggestive of the condition .presented. A portion of artery with its branches becomes elongated and widened, and the vessels become convoluted like varicose veins. Sometimes the dilatation extends to the corresponding capillaries and veins. This, form of aneurysm occurs most frequently in the arteries of the scalp and face, especially the temporal and occipital, and the enlarged and tortuous vessels are to be felt under the skin. The Aneurysm by anastomosis is almost an arterial vascular tumour. There is enlargement and lengthening of a large number of small arteries, with probably new-formation of arteries, and the mass of vessels can be felt like pulsating worms under the skin. The enlargement may extend to the capillaries. The affection forms a distinct growth of a bluish-red colour, with a somewhat granular surface. Its most frequent' seat is the scalp.
This arises in consequence of an injury to a vessel. An injury has been sustained, and after a longer or shorter period an aneurysm appears. The mode in which such aneurysms arise varies. In some cases an artery is wounded, and the blood makes a cavity for itself, constituting a Spurious aneurysm. The cavity remains in communication with the artery, and forms a kind of aneurysmal sac. This is not a common result of wounds of arteries, as, these usually close, but it does occur, and most readily when the wound has been an oblique or longitudinal one. It may result from a penetrating wound of such a form as to prevent the escape of the blood from the surface, or it may result from a broken bone tearing the coats.
But there are some cases of traumatic aneurysm which are more slow of formation and in which it is not probable that any distinct tear through the whole coats has occurred. In the fully developed aneurysm it is impossible to trace the exact mode of origin, but it is probable that in many cases a fractured bone projected against a vessel injures or even ruptures the middle coat, and possibly the internal as well. We know that in applying a ligature those two coats give way, and we can conceive a violent force applied to the wall producing the same result. A simple blow may act in a similar way, but it will do so the more readily if the middle coat be already brittle from calcareous infiltration. Many of the aneurysms of the femoral and popliteal arteries are referred to blows and injuries; but these are not all to be regarded as pure traumatic aneurysms, as the arterial coats are frequently so altered by atheroma and calcareous infiltration as to make the injury merely the determining cause.
Traumatic aneurysms, as appears from what has been said as to their origin, have usually less defined sacs than spontaneous ones. This is especially the case in those which arise directly from wounds.
In this .form the blood is not in a distinct sac, but is within the coats of the artery itself, a false passage being formed amongst the layers of the middle coat. The blood finds its way into this situation by rupture of the intima and internal layers of the media. It sometimes arises from an injury, and is thus a traumatic aneurysm, but it more frequently occurs spontaneously, and it is frequently multiple. The author has met with a case in which there were four separate dissecting aneurysms on the aorta and its branches. It may be inferred from this fact that the condition is often due to an abnormal brittleness of the internal coat, apparently not from atheroma or any other definite disease of the coat, but an inherited or acquired brittleness. The internal coat is torn through, and the blood passes among the fibres of the middle coat. It is not that the middle coat is dissected up from the internal coat, but the layers of the middle coat itself are separated, and the blood lies between an external and an internal layer of the middle coat, as in Fig. 256. The splitting up of the middle coat may be carried a considerable distance, and after passing along in the wall of the vessel the blood may make another tear in the internal coat and pass back into the vessel. The aneurysm may thus come to have two apertures, and a condition may occur as if the vessel were formed of a double tube, divided longitudinally by a septum composed of the internal and a part of the middle coat (see Fig. 255). The circulation may even be carried on to a great extent through the aneurysm, the blood passing in at the original aperture and out at the secondary one. In the case already referred to and partly shown in Fig. 255, one of the aneurysms began in the thoracic aorta, and was continued down into the iliac arteries. There were two apertures, one in the thoracic, and the other far down in the abdominal aorta, and between these the aneurysm had evidently carried on the circulation to a greater extent than the natural channel. The approximation of such an aneurysm in character to the regular channel is still further increased by the fact that the aneurysm by and by acquires an internal lining resembling the internal coat. It is a homogeneous membrane of about the thickness of the internal coat, so that in a section it may be difficult, even under the microscope, to say whether a particular place is wall of vessel or wall of aneurysm (see Fig. 256). In that case the proper calibre of the artery may become considerably narrowed.
Fig. 255. - Dissecting aneurysm of aorta. In A, a longitudinal section shows the two tubes, the natural calibre a, and the aneurysmal one b b, the latter largely occupied by clot. The hollow of the arch is largely occupied by clot at c, there being here a partial rupture of the coats. B is a transverse section. The proper calibre is greatly reduced, and the separation has extended round about three-fourths of the circumference. (From a preparation in the Western Infirmary Museum).
Dissecting aneurysms being confined to the wall of the vessel appear externally as thickenings or dilatations of the wall, and they may produce bulging or bagging of the vessel to a remarkable degree. Occasionally a dissecting aneurysm tears through the remaining layers of the middle coat and the external coat, and so a spurious aneurysm is attached to a dissecting one.
(d) Varicose aneurysm is a term applied to the case in which an artery and a vein acquire a permanent abnormal communication. It may arise spontaneously or traumatically. This form used to be not uncommon at the bend of the elbow, when, in performing venesection, the lancet wounded artery and vein together. It occurs spontaneously when an aneurysm ruptures into a vein. In some cases there is an actual aneurysmal sac between artery and vein, and to this form the name Varicose aneurysm is more properly applied. But the communication may be •direct, and while the artery is little dilated the vein is enlarged, tortuous, and pulsating. To this form the name Aneurysmal varix is applied. The interference with the venous current produced by the violent injection of the arterial blood, especially if it be suddenly produced, may lead to serious venous engorgement and oedema, which may even have a fatal issue. Spontaneous communications of this kind have been observed in cases of bursting of aneurysms between the aorta and venae cavse, between the crural and popliteal arteries and the corresponding veins, between the splenic artery and azygos vein, and between the internal carotid and the sinus cavernosus.
Fig. 250. - Section of portion of a dissecting aneurysm of the aorta. At the left there is the entire wall of the artery, a being external, b middle, and c internal coat. The middle coat is split so as to form the aneurysm. At. d d,a kind of internal coat is formed to the aneurysm, but this is the seat of fatty degeneration at c, x l6.