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 (Fig.
15.44). Aneurysms can
also be grouped according to their shape [fusiform, saccular (Fig.
15.45),
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.
Symptoms
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
Intrinsic
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.
Extrinsic
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.
Differential diagnosis
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
Pulsating
tumours include bone sarcoma, osteoclastoma and metastasis, especially from a
hypernephroma.
An abscess
Before
making an incision into a swelling believed to be an abscess, e.g. of the chest
wall (Fig. 15.46), 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.