Arterial dilatation (aneurysm)
Dilatations of localised segments of the arterial system are called aneurysms. They can either be true aneurysms, containing the three layers of the arterial wall in the aneurysm sac, or false aneurysms, having a single layer of fibrous tissue as the wall of the sac, e.g. aneurysm following trauma. Aneurysms can also be grouped according to their shape [fusiform, saccular, dissecting], or to their aetiology [atherosclerotic, traumatic, syphilitic, collagen disease (Marfan’s syndrome), mycotic]. The term mycotic is a misnomer because, while it indicates infection as a causal element in the formation of the aneurysm, this is hardly ever due to a fungus. In general, mycotic aneurysms are due to bacteria. Aneurysms occur all over the body in major vessels such as the aorta, femoral, popliteal, subclavian and carotid arteries, or in smaller vessels, such as the cerebral, mesenteric, splenic and renal arteries. The majority is true fusiform atherosclerotic aneurysms.
All aneurysms can cause symptoms due to expansion, thrombosis, rupture or the release of emboli. The symptoms relate to the vessel affected, the site supplied or the tissues compressed by the aneurysm. Emboli from an aortic aneurysm can occasionally cause ischaemia of the toes and thrombotic occlusion of a popliteal aneurysm is a well-recognised cause of gangrene of the foot.
Clinical features of an aneurysm
A swelling exhibiting expansile pulsation is present in the course of an artery. The pulsation diminishes if proximal pressure can be applied; the sac itself is compressible (although large aneurysms are frequently full of mural thrombus and may not be compressible), filling again in two or three beats if proximal pressure is released. A thrill may be palpable and auscultation sometimes reveals a bruit.
Neighbouring or distal structures are affected. Thus pressure on veins or nerves causes distal oedema or altered sensation. Bones, joints or tubes, such as the trachea or oesophagus, are sometimes affected, but structures which are resilient, such as the intervertebral discs, often withstand prolonged pressure.
Swelling under an artery
An artery may be pushed forwards, e.g. the subclavian by a cervical rib, and thus rendered prominent. Careful palpation distinguishes this condition.
Swelling over an artery
Transmitted pulsation is liable to be mistaken for that caused by expansion. However, posture may diminish pulsation; thus a pancreatic cyst examined in the genupectoral position falls away from the aorta, and consequently pulsation is less definite.
Pulsating tumours include bone sarcoma, osteoclastoma and metastasis, especially from a hypernephroma.
Before making an incision into a swelling believed to be an abscess, e.g. of the chest wall, in the groin, in the axilla or in the popliteal fossa, it is essential to make sure that it does not pulsate. This mistake has been made many times.
A serpentine artery
A serpentine artery, e.g. innominate, carotid.
No comments yet.