nonsteroidal anti-inflammatory drugs, and
sometimes antibiotic drugs. The condi-
tion usually clears up in 10–14 days.
thrombosisThe formation of a thrombus
(blood clot) in an undamaged blood
vessel. A thrombus that forms within an
artery supplying the heart muscle (coro-
nary thrombosis) is the usual cause of
myocardial infarction. A thrombus in an
artery of the brain (cerebral thrombosis)
is a common cause of stroke. Thrombi
sometimes form in veins,either just
below the skin or in deeper veins (see
thrombosis, deep vein).
In arteries, thrombus formation may
be encouraged by atherosclerosis, smok-
ing, hypertension, and damage to blood
vessel walls from arteritisand phlebitis.
An increased clotting tendency may occur
in pregnancy, when using oral contra-
ceptives, or through prolonged immobility.
An arterial thrombosis may cause no
symptoms until blood flow is impaired.
Then, there is reduced tissue or organ
function and sometimes severe pain.
Venous thrombosis may also cause
pain and swelling. Diagnosis is made by
doppler ultrasound. In some cases, ang-
iographyor venographymay also be
used. Treatment may include anticoag-
ulant drugs or thrombolytic drugs,
nonsteroidal anti-inflammatory drugs,and
antibiotic drugs. In life-threatening cases,
thrombectomymay be needed.
thrombosis, deep veinThe formation
of a thrombuswithin deep-lying veins in
the leg. The cause is usually a combina-
tion of slow blood flow through 1 part
of the body (such as when sitting for
long periods or when the tissues are
compressed, as occurs in long-haul air-
craft flights) and an increase in the
clotting tendency of the blood, which
occurs with dehydration, after surgery
or injury, during pregnancy, and in
women taking oral contraceptives. Deep
vein thrombosis may also be caused by
polycythaemia. Deep vein thrombosis is
common in people with heart failure
and those who have had a strokeor who
have been immobile for long periods.
Clots in the leg veins may cause pain,
tenderness, swelling, discoloration, and
ulceration of the skin, but they can be
symptomless. A deep vein thrombosis
is not necessarily serious in itself, but
part of the clot may break off and travel
in the bloodstream to the lungs. This is
known as a pulmonary embolism.
A diagnosis is made by doppler ultra-
sound scanning. Treatment depends on
the site and extent of the clots. Small
clots may not need treatment if they are
confined to the calf and the patient is
mobile. Otherwise, anticoagulant drugs
or thrombolytic drugsare given. If there
is a high risk of a pulmonary embolism,
thrombectomymay be performed.
thrombusA blood clot that has formed
inside an intact blood vessel. A throm-
bus is life-threatening if it obstructs the
blood supply to an organ such as the
heart or brain. A thrombus may also
lead to gangrenein an organ or extrem-
ity, or to embolism. (See also blood
clotting; thrombosis.)
thrushA common name for the fungal
infection candidiasis.
thumb-suckingA common habit in
young children, which provides comfort,
oral gratification, amusement when
bored, and reassurance. Thumb-sucking
tends to decrease after age 3, and most
children grow out of it by age 7. In most
cases, it is not harmful. However, maloc-
clusionof the permanent teeth may
develop if the habit continues past age- This is usually temporary; if not, an
orthodontic appliancemay be needed.
thymomaA rare tumourof the thymus
gland.The tumour can arise from any of
the cell types in the thymus gland and
can be cancerous or noncancerous.
thymoxamineSee moxisylyte.
thymusA gland that forms part of the
immune system. The thymus lies behind
the sternumand consists of 2 lobes that
join in front of the trachea. Each lobe is
made of lymphoid tissue consisting of
lymphocytes, epithelium, and fat. The
thymus conditions lymphocytes to
become T-cells. It plays a part in the
immune response until puberty, gradu-
ally enlarging during this time. After
puberty, it shrinks, but some glandular
tissue remains until middle-age.
thyroglossal disordersA set of con-
genital defects caused by failure of the
thyroglossal duct to disappear during
embryonic development. In embryos,
THROMBOSIS THYROGLOSSAL DISORDERS
T