Pyogenic.—Non-suppurative inflammation of the coats of an artery may so soften the wall of the vessel as to lead to aneurysmal dilatation. It is not uncommon in children, and explains the occurrence of aneurysm in young subjects.
When suppuration occurs, the vessel wall becomes disintegrated and gives way, leading to secondary hæmorrhage. If the vessel ruptures into an abscess cavity, dangerous bleeding may occur when the abscess bursts or is opened.
Syphilitic.—The inflammation associated with syphilis results in thickening of the tunica intima, whereby the lumen of the vessel becomes narrowed, or even obliterated—endarteritis obliterans. The middle coat usually escapes, but the tunica externa is generally thickened. These changes cause serious interference with the nutrition of the parts supplied by the affected arteries. In large trunks, by diminishing the elasticity of the vessel wall, they are liable to lead to the formation of aneurysm.
Changes in the arterial walls closely resembling those of syphilitic arteritis are sometimes met with in tuberculous lesions.
Arterio-sclerosis or Chronic Arteritis.—These terms are applied to certain changes which result in narrowing of the lumen and loss of elasticity in the arteries. The condition may affect the whole vascular system or may be confined to particular areas. In the smaller arteries there is more or less uniform thickening of the tunica intima from proliferation of the endothelium and increase in the connective tissue in the elastic lamina—a form of obliterative endarteritis. The narrowing of the vessels may be sufficient to determine gangrene in the extremities. In course of time, particularly in the larger arteries, this new tissue undergoes degeneration, at first of a fatty nature, but progressing in the direction of calcification, and this is followed by the deposit of lime salts in the young connective tissue and the formation of calcareous plates or rings over a considerable area of the vessel wall. To this stage in the process the term atheroma is applied. The endothelium over these plates often disappears, leaving them exposed to the blood-stream.
Changes of a similar kind sometimes occur in the middle coat, the lime salts being deposited among the muscle fibres in concentric rings.
The primary cause of arterio-sclerosis is not definitely known, but its almost constant occurrence, to a greater or less degree, in the aged suggests that it is of the nature of a senile degeneration. It is favoured by anything which throws excessive strain on the vessel walls, such as heavy muscular work; by chronic alcoholism and syphilis; or by such general diseases as tend to raise the blood-pressure—for example, chronic Bright's disease or gout. It occurs with greater frequency and with greater severity in men than in women.
Atheromatous degeneration is most common in the large arterial trunks, and the changes are most marked at the arch of the aorta, opposite the flexures of joints, at the mouths of large branches, and at parts where the vessel lies in contact with bone. The presence of diseased patches in the wall of an artery diminishes its elasticity and favours aneurysmal dilatation. Such a vessel also is liable to be ruptured by external violence and so give rise to traumatic aneurysm. Thrombosis is liable to occur when calcareous plates are exposed in the lumen of the vessel by destruction of the endothelium, and this predisposes to embolism. Arterio-sclerosis also interferes with the natural arrest of hæmorrhage, and by rendering the vessels brittle, makes it difficult to secure them by ligature. In advanced cases the accessible arteries—such as the radial, the temporal or the femoral—may be felt as firm, tortuous cords, which are sometimes so hard that they have been aptly compared to “pipe-stems.” The pulse is smaller and less compressible than normal, and the vessel moves bodily with each pulsation. It must be borne in mind, however, that the condition of the radial artery may fail to afford a clue to that of the larger arteries. Calcified arteries are readily identified in skiagrams (Fig. 65).
We have met with a chronic form of arterial degeneration in elderly women, affecting especially the great vessels at the root of the neck, in which the artery is remarkably attenuated and dilated, and so friable that the wall readily tears when seized with an artery-forceps, rendering ligation of the vessel in the ordinary way well-nigh impossible. Matas suggests infolding the wall of the vessel with interrupted sutures that do not pierce the intima, and wrapping it round with a strip of peritoneum or omentum.
The most serious form of arterial thrombosis is that met with in the abdominal aorta, which is attended with violent pains in the lower limbs, rapidly followed by paralysis and arrest of the circulation.