gallstones or tumours (see
rarely, the ducts are absent
from birth (see
obstruction and biliary atresia are often
A rare but serious con-
dition in which skin cells proliferate and
grow inwards from the ear canal into the
middle ear. Cholesteatoma usually occurs
as a result of long-standing
together with a defect in the eardrum
it may damage the small bones in the
middle ear and other structures. Choles-
teatoma needs to be removed surgically
through the eardrum or by
A fat-like substance that is
an important constituent of body cells
and is also involved in the formation of
hormones and bile salts. Cholesterol in
the blood is made by the liver from
foods, especially saturated fats, although
a small amount is absorbed directly
from cholesterol-rich foods such as eggs.
High blood cholesterol levels increase
the risk of
, and with it the
coronary artery disease
In general, cholesterol transported in the
blood in the form of low-density lipo-
(LDLs) or very low-density
lipoproteins (VLDLs) is a risk factor for
these conditions, while cholesterol in
the form of high-density lipoproteins
(HDLs) seems to protect against arterial
disease. Blood cholesterol levels are in-
fluenced by diet, heredity, and metabolic
diseases such as
can be measured by blood tests. Levels
below 5.2 mmol/L are acceptable; higher
levels may require further tests. Dietary
changes can lower cholesterol slightly;
drugs such as
An alternative spelling
Inflammation of a
usually caused by pressure, stress, or
injury. Costochondritis is inflammation
affecting the cartilage between the ribs
and the sternum (breastbone).
A prefix denoting a relation-
, as in chondrocyte, a
cell that produces cartilage.
, affecting the bones.
Chondromas most often occur in the
hands and feet (see
disorder of the knee in which the carti-
lage behind the patella (kneecap) is
damaged. Adolescents are most com-
monly affected. The condition may result
from knee injuries or sporting activities
in which the knee is bent for long per-
iods. This action weakens the inner part
of the quadriceps muscle (at the front of
the thigh) causing the patella to tilt
when the knee is straightened and rub
against the lower end of the
cartilage that covers both bones becomes
roughened, causing pain and tender-
ness. Treatment is with
and exercises to strengthen the thigh
muscles. Rarely, surgery may be needed.
A condition in which
multiple noncancerous tumours, called
, arise in the bones, most
commonly the bones of the hands and
feet. The tumours consist of
cells and usually cause no symptoms.
A cancerous growth
occurring within or on the
surface of large bones, causing pain and
swelling. Usually occurring in middle age,
the tumour develops slowly from a non-
or from normal bone.
of the bone above the tumour
usually results in a permanent cure.
Abnormal curvature of the penis,
occurs in males with
birth defect in which the urethral open-
ing lies on the underside of the penis.
Corrective surgery is usually performed
between the ages of 1
and 3 years.
A condition characterized by
irregular, rapid, jerky movements, usu-
ally affecting the face, limbs, and trunk.
It is a feature of
and may occur
in pregnancy. Chorea may also be a side
effect of certain drugs, including
; certain drugs for psychi-
atric disorders; and drugs for treating
. Symptoms usually
disappear when the drug is withdrawn.
Underlying causes of chorea are treated
with drugs that inhibit nerve pathways
concerned with movement.