LIVER CYSTS HYDATID ECHINOCOCCAL CYST
Category: Diagnostic Radiology
Abstract : BENIGN FOCAL LIVER LESIONS Simple cysts One of the most frequently seen
liver lesions, the simple cyst, is either congenital (from abnormal development
of a biliary radicle) or acquired (from trauma or previous infection). It is
asymptomatic, unless large enough to cause a ‘mass effect’, compressing and
displacing adjacent structures, and is usually an incidental finding
BENIGN FOCAL LIVER LESIONS
Simple cysts
One of the most frequently seen
liver lesions, the simple cyst, is either congenital (from abnormal development
of a biliary radicle) or acquired (from trauma or previous infection). It is
asymptomatic, unless large enough to cause a ‘mass effect’, compressing and
displacing adjacent structures, and is usually an incidental finding during the
ultrasound scan.
Frequently, small cysts are peripheral and therefore more
likely to be missed on ultrasound than CT.
The simple cyst has three
acoustic properties, which are pathognomonic; it is anechoic, has a well-defined
smooth capsule and exhibits posterior enhancement (increased throughtransmission
of sound). Although theoretically it is possible to confuse a simple cyst with a
choledochal cyst, the latter’s connection to the biliary tree is usually
demonstrable on ultrasound. A radioisotope hepatic iminodiacetic acid (HIDA)
scan will confirm the biliary connection if doubt exists.
Complex
cysts
Some cysts may contain a thin septum, which is not a significant
finding. However, cysts which contain solid nodules or thickened walls should be
viewed with suspicion. Occasionally haemorrhage or infection may occur in a
simple cyst, giving rise to low-level, fine echoes within it.
These cysts
are not usually actively treated; however the larger ones may be monitored with
ultrasound, particularly if symptomatic. Percutaneous aspiration of larger cysts
under ultrasound guidance may afford temporary decompression but is rarely
performed as they invariably recur. Laparoscopic unroofing provides a more
permanent solution to large, symptomatic cysts.
Another uncommon cause of
a cystic lesion in the liver is a cystadenoma — a benign epithelial tumour.
These have the potential to turn malignant, forming a cystadenocarcinoma. Close
monitoring with ultrasound will demonstrate a gradual increase in size, changes
in the appearances of the wall of the cyst, such as thickening or papillary
projections, and internal echoes in some cases, which may arouse suspicion. A
diagnostic aspiration may be performed under ultrasound guidance, and the fluid
may contain elevated levels of carcinoembryonic antigen if malignant.
Cystadenomas are usually surgically removed due to their malignant potential.
Rarely, cystic lesions in the liver may be due to other causes. These include
pancreatic pseudocyst (within an interlobular fissure) in patients with acute
pancreatitis or mucin-filled metastatic deposits in primary ovarian cancer. An
arteriovenous malformation, a rare finding in the liver, may look like a
septated cystic lesion. Doppler, however, will demonstrate flow throughout the
structure.
Polycystic liver
There is a fine dividing line between a
liver which contains multiple simple cysts and polycystic liver disease. The
latter usually occurs with polycystic kidneys, a common autosomal dominant
condition readily recognizable on ultrasound, but may rarely affect the liver
alone. The appearances are of multiple, often septated cysts, of varying sizes
throughout the liver. The cumulative enhancement behind the numerous cysts
imparts a highly irregular echogenicity to the liver texture and may make it
extremely difficult to pick up other focal lesions which may be present. The
polycystic liver is usually asymptomatic, but easily palpable, and if the
kidneys are also affected the abdomen can look very distended. As with cysts in
the kidneys, haemorrhage or infection in a cyst can cause localized pain.
Treatment of the cysts by drainage is not successful and in rare cases hepatic
transplant offers the only viable option in patients with intractable
symptoms.
Hydatid (echinococcal) cyst
Hydatid disease comes from a
parasite, Echinococcus granulosus, which is endemic in the Middle East but rare
in the UK. The worm lives in the alimentary tract of infected dogs, which
excrete the eggs. These may then be ingested by cattle or sheep and subsequently
complete their life cycle in a human. The parasite spreads via the bloodstream
to the liver, where it lodges, causing an inflammatory reaction. The resulting
cyst can be slow-growing and asymptomatic and may be single or multiple,
depending on the degree of infestation. Although the appearances are often
similar to those of a simple cyst, the diagnosis can be made by looking
carefully at the wall and contents; the hydatid cyst has two layers to its
capsule, which may appear thickened, separated or detached on ultrasound.
Daughter cysts may arise from the inner capsule— the honeycomb or cartwheel
appearance. Thirdly, a calcified rind around a cyst is usually associated with
an old, inactive hydatid lesion. The diagnosis of hydatid, as opposed to a
simple cyst, is an important one as any attempted aspiration may spread the
parasite further by seeding along the needle track if the operator is unaware of
the diagnosis.
Management of hepatic hydatid cysts has traditionally been
surgical resection. However, considerable success has now been achieved using
percutaneous ultrasound-guided aspiration with sclerotherapy.
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