gallstones or tumours (see bile duct
obstruction); rarely, the ducts are absent
from birth (see biliary atresia). Bile duct
obstruction and biliary atresia are often
treated surgically.
cholesteatomaA 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 otitis media
together with a defect in the eardrum
(see eardrum, perforated). Left untreated,
it may damage the small bones in the
middle ear and other structures. Choles-
teatomaneeds to be removed surgically
through the eardrum or by mastoidectomy.
cholesterolA 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 atherosclerosis, and with it the
risk of coronary artery diseaseor stroke.
In general, cholesterol transported in the
blood in the form of low-density lipo-
proteins (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 diabetes mellitus,and
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 simvastatinachieve a
greater reduction.
cholestyramineAn alternative spelling
for colestyramine.
chondritisInflammation of acartilage,
usually caused by pressure, stress, or
injury. Costochondritis is inflammation
affecting the cartilage between the ribs
and the sternum (breastbone).
chondro-A prefix denoting a relation-
ship to cartilage, as in chondrocyte, a
cell that produces cartilage.
chondromaA noncancerous tumour
composed of cartilage, affecting the bones.
Chondromas most often occur in the
hands and feet (see chondromatosis).
chondromalacia patellaeA painful
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 femur. The
cartilage that covers both bones becomes
roughened, causing pain and tender-
ness. Treatment is with analgesic drugs
and exercises to strengthen the thigh
muscles. Rarely, surgery may be needed.
chondromatosisA condition in which
multiple noncancerous tumours, called
chondromas, arise in the bones, most
commonly the bones of the hands and
feet. The tumours consist of cartilage
cells and usually cause no symptoms.
chondrosarcomaA cancerous growth
of cartilageoccurring within or on the
surface of large bones, causing pain and
swelling. Usually occurring in middle age,
the tumour develops slowly from a non-
cancerous tumour (see chondroma;
dyschondroplasia) or from normal bone.
Amputationof the bone above the tumour
usually results in a permanent cure.
chordeeAbnormal curvature of the penis,
usually downwards. Chordee mainly
occurs in males with hypospadias, a
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.
choreaA condition characterized by
irregular, rapid, jerky movements, usu-
ally affecting the face, limbs, and trunk.
It is a feature of Huntington’s disease
and Sydenham’s chorea,and may occur
in pregnancy. Chorea may also be a side
effect of certain drugs, including oral
contraceptives; certain drugs for psychi-
atric disorders; and drugs for treating
Parkinson’s disease. Symptoms usually
disappear when the drug is withdrawn.
Underlying causes of chorea are treated
with drugs that inhibit nerve pathways
concerned with movement.CHOLESTEATOMA CHOREA
C