Cysts
The word cyst is derived from the Greek word meaning ‘bladder’. The
pathological term ‘cyst’ means a swelling consisting of a collection of
fluid in a sac which is lined by epithelium or endothelium.
True
cysts
True cysts are lined by epithelium or endothelium. If infection
supervenes, the true lining may be destroyed and replaced by granulation tissue.
The fluid is usually serous or mucoid and varies from brown-staining by altered
blood to almost colourless. In epidermoid, dermoid and branchial cysts the
contents are like porridge or toothpaste, as a result of the shedding of
desquamated cells. Cholesterol crystals are often found in the fluid of
branchial cysts.
False
cysts (pseudocysts)
Walled-off collections of fluid not lined by epithelium are not regarded
as true cysts. A pseudocyst of the pancreas is an encysted collection of
pancreatic enzymerich fluid lined by granulation tissue or fibrous tissue.
Pancreatic pseudocysts are often in the retroperitoneum deep to but bulging into
the lesser sac; they may occur anywhere in the abdominal cavity and even track
into the mediastinum and pleural cavities. In tuberculous peritonitis, fluid may
be walled off in cystic form by adherent coils of intestine. Fluid may collect
in the centre of a tumour (cystic degeneration), due to haemorrhage or necrosis.
This can also happen in the brain as a result of ischaemia, and an ‘apoplectic
cyst’ is formed. In acute pancreatitis fluid collections loculated by viscera
and fibrin are called ‘acute fluid collections’; these often occur in the
lesser sac but are neither cysts nor pseudocysts as they are not lined by either
epithelium, granulation tissue or fibrous tissue.
A
classification of cysts
Congenital
Sequestration dermoids
Tubuloembryonic (tubulodermoid)
Cyst of embryonic remnants
Acquired
Retention
Distention
Exudation
Cystic tumours
Implantation dermoids
Trauma
Degeneration
Parasitic
Hydatid, trichniasis, cysticercosis
The sequestration dermoid is due to dermal cells being buried along the
lines of closure of embryonic clefts and sinuses by skin fusion. The cyst
therefore is lined by epidermis and contains paste-like desquamated material.
The usual sites are:
• the midline of the body — especially in the neck;
• above the outer canthus (external angular dermoid, Chapter 35);
• in the anterior triangle of the neck (branchial cyst, Chapter
43).
Tubuloembryonic (tubulodermoid) cysts occur in the track of an
ectodermal tube used in development, e.g. a thyroglossal cyst from the
thyroglossal duct or a postanal dermoid from the postanal gut. In the brain,
ependymal cysts arise from the sequestration of cells of the enfolding
neurectoderm.
Cysts
of embryonic remnants. These arise from embryonic tubules and ducts which
normally disappear or are only present as remnants. They should not be
confused with teratomatous cysts, e.g. dermoid. There are many examples in
the urogenital system, e.g. in the male from remnants of the paramesonephric
duct (Müllerian) — the hydatid of Morgagni, or from the mesonephric body
and duct (Wolffian) (Chapter 64). Cysts of the urachus and the vitellointestinal
duct are other examples of cysts of embryonic remnants (Chapter 65).
Acquired
cysts
Retention cysts are due to the accumulated secretion of a gland behind
an obstruction of a duct. Examples are seen in the pancreas, the parotid, the
breast, the epididymis and Bartholin’s gland. A sebaceous cyst starts with the
obstruction of a sebaceous gland, but this is followed by the down-growth and
the accumulation of desquamated epidermal cells, thus turning it into an
epidermoid cyst. In the epididymis, if the retention cyst contains sperms, it is
known as a ‘spermatocele’.
Distension
cysts occur in the thyroid from dilatation of the acini, or in the ovary from a
follicle. Lymphatic cysts and cystic hygromas are distension cysts. Exudation
cysts occur when fluid exudes into an anatomical space already lined by
endothelium, e.g. hydrocele, a bursa, or when a collection of exudate becomes
encrusted.
Cystic
tumours. Examples are cystic teratomas (dermoid cyst of the ovary) and
cystadenomas (pseudomucinous and serous cystadenoma of the ovary).
Ganglia.
See Chapter 29.
Implantation
dermoids arise from squamous epithelium which has been driven beneath the skin
by a penetrating wound. They are classically found in the fingers of women who
sew assiduously and metal workers (Fig. 12.13).
Trauma
A haematoma may resolve into a cyst. This sometimes happens to
haematomas of muscle masses in the loin and anterolateral aspects of the thigh
or the skin. They are located between muscle, facial or subcutaneous planes
and contain straw- or brown-coloured fluid containing cholesterol crystals. They
become lined by endothelium and calcium salts may be laid down. Aspiration is
only of temporary value, and a cure depends upon complete excision of the
lining. Within the cranium, a haematogenous cyst can cause the same problems as
any expanding, space-occupying lesion.
Degeneration
cysts
These have already been discussed under false cysts.
Parasitic
cysts
These are encrusted forms in the life cycle of various worms:
• Hydatid cyst of Taenia
echinococcus. This is described later according to the organ involved, e.g.
liver, Chapter 52; lung, Chapter 47.
• Trichiniasis. Cysts of Trichina
spiralis, affecting muscle.
• Cysticercosis. Cysts
of Taenia solium. A disease of the pig, humans being rarely affected. Eosinophilia
is present. The cysts occur in any organ. They calcify and may
cause clinical effects according to their situation, especially in the brain.
Only those cysts which are actually causing symptoms should be excised.
Clinical
features
The swelling usually has a smooth, spherical appearance. Fluctuation depends
upon the pressure of fluid within: a tense cyst feels like a solid tumour,
although careful palpation between two fingers may elicit a characteristic
elasticity. In addition, a solid tumour is most hard at the centre; a cyst is
least hard at the centre. If fluctuation is present, a cyst may be confused
with a cold abscess or a lipoma. A cold abscess usually has a peculiar rim of
thickening surrounding the soft centre. A lipoma may well test clinical acumen. Transillumination,
while brilliantly clear in cysts containing serous fluid, does not really
distinguish between a lipoma and a dermoid or branchial cyst. There is even an
old axiom that ‘when in doubt, hedge on fat’. According to circumstances,
ultrasonography, computerised tomography (CT) or magnetic resonance imaging (MRI),
a test aspiration or excision reveals the true nature of the swelling.
Cysts
may be painful, especially when infection or haemorrhage causes a sudden
increase in intracystic tension. Sometimes they change in size for no apparent
reason. Occasionally, they diminish owing to rupture through a facial plane.
Effects
are according to site and size. As with benign tumours, a cyst may compress
ducts and blood vessels, e.g. the main bile duct may be obstructed by a
choledochal cyst, a renal cyst or a hydatid cyst. The pelvic veins may be
obstructed by an ovarian cyst, the patient presenting for treatment of her
varicose veins. The sheer size of an ovarian cyst (Fig.
12.14) may so increase
intra-abdominal tension as to bring the patient to hospital with symptoms of a
hiatus hernia.
Complications
Infection
The cyst becomes tense and painful, and adherent to surrounding
tissues. An abscess may form and discharge on the surface and result in an ulcer
or a sinus (viz. Cock’s peculiar tumour, Chapter 13). Healing will not occur
until the whole lining of the cyst or the embryonic track is excised.
Haemorrhage
Sudden haemorrhage, as may occur in a thyroid cyst, causes a painful
increase in size. In this particular case, breathing may be difficult because of
pressure on the trachea.
Torsion
Torsion may occur in cysts which are attached to neighboring structures by a vascular pedicle. Ovarian dermoids are sometimes brought to
notice in this way as acute abdominal emergencies. The cyst (or cysts — they
may be bilateral) turns to a purple or black colour as the venous and then the
arterial supply is cut off.
Calcification
Calcification follows haemorrhage, or infection, and may be the result
of reaction to a parasite, e.g. hydatid cyst.
Cachexia
ovarica