epilepsy, irritability, lethargy, and the
absence of normal reflex actions. If it is
not treated, hydrocephalus progresses
to severe brain damage, which may
result in death within weeks. When the
condition occurs later in life, symptoms
include headache, vomiting, loss of
coordination, and the deterioration of
mental function.
In most cases, treatment of hydro-
cephalus is by draining the fluid from
the brain to another part of the body,
such as the abdominal cavity, where it
can be absorbed.
hydrochloric acidA strong acid re-
leased by the stomach lining. This acid
forms part of the stomach juices and
helps to digest proteins.
hydrochlorothiazideA thiazide diur-
etic drugused to reduce oedemain
people with heart failure, nephrotic syn-
drome, and cirrhosis. It is also given for
hypertension. Adverse effects include
leg cramps, dizziness, rash, and impo-
tence. The drug may rarely cause gout
and may aggravate diabetes mellitus.
hydrocortisoneA hormoneproduced
naturally by the adrenal glands. Syn-
thetic hydrocortisone is used as a
corticosteroid drugto treat inflammatory
or allergic conditions, such as ulcerative
colitisor dermatitis. Used in excess, hydro-
cortisone creams may thin the skin.
hydrogen peroxideAn antisepticsol-
ution used to treat infections of the skin
or mouth and to bleach hair.
hydronephrosisA condition in which
a kidneybecomes swollen with urine as
a result of an obstruction in the urinary
tract. Many people with hydronephrosis
have a congenitalnarrowing of the ure-
ter. The obstruction of a ureter may be
caused by a stone (see calculus, urinary
tract), a kidney tumour, or a blood clot.
Occasionally, hydronephrosis is caused
by obstruction to the outflow of urine
from the bladder by an enlarged pros-
tate gland (see prostate, enlarged).
Acute hydronephrosis, with sudden
blockage of the ureter, causes severe
pain in the loin. Chronic hydronephro-
sis, in which the obstruction develops
slowly, may cause no symptoms until
total blockage results in kidney failure. If
the blockage can be removed surgically,
the kidney is likely to function normally
again. Occasionally, however, a kidney is
so badly damaged that it requires re-
moval (see nephrectomy).
hydrophobiaA popular term, now al-
most obsolete, for rabies.
hydropsAn abnormal accumulation of
fluid in body tissues or in a sac.
hydrops fetalisSerious swelling, or
oedema,that occurs in a fetusbefore
birth. Hydrops fetalis is often the result
of Rhesus incompatibility(see haemolytic
disease of the newborn).
hydrotherapyThe use of exercises in
water to aid recovery from injury or
improve mobility. Cold baths after an
injury can reduce swelling and bruising.
(See also heat treatment; ice-packs.)
hydroxocobalaminA long-acting syn-
thetic preparation of vitamin B 12 , given
by injection.
hygieneThe science and practice of
preserving health. The word hygiene is
commonly equated with cleanliness, but
it can also refer to public health.
hygiene, oralSee oral hygiene.
hygroma, cysticA lymphangiomathat
occurs around the head and neck, the
armpits, or the groin and contains clear
fluid. Cystic hygromas are usually pre-
sent from birth and disappear naturally
from the age of about 2.
hymenThe thin membrane around the
vaginal opening. The hymen has a central
perforation which is usually stretched
or torn by the use of tampons or during
sexual intercourse for the 1st time.
Imperforate hymen is a rare condition
in which the hymen has no perforation;
at the onset of menstruation, menstrual
blood collects in the vagina, causing
lower abdominal pain. The condition is
easily corrected by a minor operation.
hyoidA small, U-shaped bone situated
centrally in the upper part of the neck. It
is not joined to any other bone but is
suspended by ligaments from the base
of the skull. It provides an anchor point
for the muscles of the tongue and of the
upper front part of the neck.
hyoscineAn anticholinergic drugpre-
scribed in 2 distinct forms. Hyoscine
butylbromide is used to relieve irritable
bowel syndrome. Hyoscine hydrobromide
is used to control motion sicknessand toHYDROCHLORIC ACID HYOSCINE
H