errors of) in which there is an abnormal
accumulation of substances known as
mucopolysaccharides in the tissues.
Affected children may appear normal
at birth but, at 6–12 months of age, they
develop cardiac abnormalities, umbil-
ical hernia, skeletal deformities, and
enlargement of the tongue, liver, and
spleen. Growth is limited and mental
development slows. If the condition is
diagnosed in early infancy, a bone mar-
row transplantmay be curative.
hydatid diseaseA rare infestation that
is caused by the larval stage of the
small tapeworm ECHINOCOCCUS GRANU-
LOSUS (see tapeworm infestation). Larvae
mostly settle in the liver, lungs, or mus-
cle, causing the development of cysts.
In rare cases, the brain is affected.
The infestation is generally confined
to dogs and sheep, but may be passed
on to humans through accidental inges-
tion of worm eggs from materials
contaminated with dog faeces.
The cysts grow slowly, and symptoms
may not appear for some years. In many
cases, there are no symptoms. Cysts in
the liver may cause a tender lump or
lead to bile duct obstructionand jaun-
dice. Cysts in the lungs may press on an
airway and cause inflammation; rupture
of a lung cyst may cause chest pain, the
coughing up of blood, and wheezing.
Cysts in the brain may cause seizures.
Ruptured cysts may rarely cause ana-
phylactic shock, which can be fatal.
Diagnosis of hydatid disease is by CT
scanningor MRI. The cysts are usually
drained or removed surgically.
hydatidiform moleAn uncommon non-
cancerous tumour that develops from
placental tissue early in a pregnancy in
which the embryo has failed to develop
normally. The mole, which resembles a
bunch of grapes, is caused by degenera-
tion of the chorionic villi. The cause of
the degeneration is unknown. In a small
number of affected pregnancies, the
mole develops into a choriocarcinoma.
Vaginal bleeding and severe morning
sickness generally occur. Ultrasound
scanningreveals the tumour. Urine and
blood tests detect excessive amounts of
human chorionic gonadotrophin (see
gonadotrophin, human chorionic), whichis produced by the tumour. The tumour
can be removed by suction, a D and C,
or, less commonly, a hysterectomy.
hydralazineAn antihypertensive drug
used principally as an emergency treat-
ment for hypertension. Hydralazine may
cause nausea, headache, dizziness, ir-
regular heartbeat, loss of appetite, rash,
and joint pain. Taken long term in high
doses it may cause lupus erythematosus.
hydramniosSee polyhydramnios.
hydroceleA soft, painless swelling in
the scrotumcaused by the space around
a testisfilling with fluid. A hydrocele
may be caused by inflammation, infec-
tion, or injury to the testis; occasionally,
the cause is a tumour. More often, there
is no apparent cause. Hydroceles com-
monly occur in middle-aged men, and
treatment is rarely necessary. If the
swelling is uncomfortable or painful,
however, the fluid may be withdrawn
through a needle. Recurrent swelling
may be treated by surgery.hydrocephalusAn excessive amount
of cerebrospinal fluid, usually under in-
creased pressure, within the skull. The
condition may be present at birth, when
it is often associated with other abnor-
malities, such as spina bifida, or it may
develop as a result of major head injury,
brain haemorrhage, infection (such as
meningitis), or a tumour.
With congenital hydrocephalus, the
main feature is an enlarged head that
continues to grow rapidly. Other features
include rigidity of the legs, vomiting,HYDATID DISEASE HYDROCEPHALUSH
Vas deferensEpididymisHydroceleScrotumHYDROCELEPenisTestis