is a Consultant Radiologist and
is Specialist Registrar in Radiology, Department of Medical
Imaging, Royal London Hospital, Whitechapel, London UK.
is a Consultant Radiologist, London Independent Hospital, London
This material in this article was presented in educational
exhibit form at the Radiological Society of North America
Meeting, December 2004.
Cystic liver lesions in adults can have a number of etiologies,
including congenital, neoplastic, and infectious conditions, as
well as trauma and miscellaneous entities. While most such cystic
lesions are benign and are frequently clinically irrelevant, the
radiologist must be able to recognize key imaging features to
enable the diagnosis of the more clinically important lesions.
Features to assess include lesion size, the presence and thickness
of a wall or any internal septations or mural nodules, the presence
of either internal or mural calcification, and the pattern of
enhancement following intravenous contrast. The importance of the
clinical history in these patients cannot be overstated.
Ultrasound, computed tomography (CT), and magnetic resonance
imaging (MRI) can act in a complementary fashion to optimize lesion
characterization. Ultrasound can reveal internal septations, mural
nodules, and debris in a lesion. CT can show wall or septal
calcification, while the signal characteristics of the cyst content
on MRI may define its contents, for example, if it is hemorrhagic.
MRI is the best imaging modality for detecting wall enhancement.
Knowledge of the imaging features of the most common types of
cystic liver lesions should enable an accurate diagnosis to be made
and should potentially avoid the need for cyst aspiration or needle
Congenital cystic lesions
Simple cysts are the most common type of cystic liver lesion and
are seen in approximately 2.5% of the population
; they are developmental, arising from a defect in bile duct
formation. On ultrasound, they are anechoic with posterior acoustic
enhancement, while on CT they are of fluid attenuation (Figure 1).
On MRI, they are of homogenously low signal intensity (SI) on
T1-weighted (T1W) imaging and high SI on T2-weighted (T2W) imaging.
An increase in the echo time (TE) will cause an increase in the SI
on T2W MRI, which is useful in discriminating cysts from metastatic
deposits. There is no discernible wall and no discernable
enhancement following the administration of either iodinated
contrast or gadolinium. Rim calcification is rare but may occur.
Possible complications include infection, rupture, torsion,
hemorrhage, and malignant transformation. But these complications
are all rare, especially the latter, though adenocarcinoma
developing in a simple cyst has been reported.
Complications may alter the imaging appearances; eg, intracyst
hemorrhage can cause increased SI on T1W MRI as well as possible
wall thickening and the development of fluid-fluid levels.
Infection may give rise to intracyst debris and septations, which
are best seen with ultrasound.
Cysts may be solitary or multiple, though if >10 cysts are
present, the possibility of polycystic liver disease should be
Autosomal dominant polycystic liver disease
Autosomal dominant polycystic liver disease is part of the
spectrum of fibro-polycystic liver diseases that are caused by
congenital bile duct malformation, including bile duct hamartoma,
Caroli's disease, congenital hepatic fibrosis, and choledochal
It is frequently seen in association with adult polycystic kidney
disease (Figure 2), although it can occur in the absence of renal
cysts. The cysts are identical-both radiologically and
histologically-to simple cysts.
Multiple cysts can cause painful hepatomegaly, a frequent
presenting complaint. Possible complications are identical to those
of simple cysts but are more frequent.
The existence of any correlation between the severity of cystic
disease in the liver with renal cystic disease is controversial.
Bile duct hamartoma
Also known as von Meyenburg complexes, bile duct hamartomas
arise from ductal plate malformations that involve the small
interlobular bile ducts.
They are seen in up to 3% of autopsy specimens
though in only 0.7% of CT studies;
44% of bile duct hamartomas are thought to be occult on CT.
They typically are small lesions that range from 2 to 15 mm in
diameter; the larger lesions may, in fact, constitute an
aggregation of smaller lesions.
They are generally scattered throughout the liver, are of uniform
size, and are rounded or oval. While there is some variability in
their imaging appearances, they are typically anechoic on
ultrasound and of fluid density on CT, low SI on T1W MRI and high
SI on T2W MRI.
Their enhancement following contrast administration is variable; no
enhancement, rim enhancement, and slow homogenous enhancement have
all been reported.
The differential diagnosis for multiple small cystic liver lesions
includes simple cysts, microabscesses, granulomata, and metastatic
disease. The small and uniform size is unusual in simple cysts and
metastasis, while clinical correlation is obviously essential to
discriminate hamartomata from other imaging possibilities. Imaging
features are ultimately nonspecific, and needle aspiration may be
required in some cases.
Caroli's disease is an autosomal recessive disorder, also known
as congenital cavernous ectasia of the biliary tree. It can be
segmental or diffuse and can cause marked saccular dilatation of
the affected bile ducts (Figure 3). Two forms have been described:
the pure form, which is associated with attacks of cholangitis and
intraductal stone formation; and the complex form, which is more
common and is associated with other ductal plate malformations.
Affected ducts are markedly dilated and contain bile and sludge,
and, occasionally, stones and pus. The ducts often have a beaded
appearance with strictured and dilated segments alternating.
Ultrasound and CT may show beaded dilated ducts, but it can be
difficult to visualize the communication of the cystic structures
to the biliary tree. Endoscopic retrograde cholangiopancreatography
(ERCP) or percutaneous transhepatic cholangiography (PTC) can be
diagnostic by showing that the dilated ducts opacify with contrast,
but these are invasive procedures and are not without risk. MRCP
has shown promise as a noninvasive imaging modality for the
diagnosis of this entity.
A hallmark of this condition on both CT and MRI is the presence of
the "central-dot sign," which is a fibrovascular bundle lying
centrally within the dilated duct that contains a portal vein
radical that enhances with contrast.
Complications include stone formation, cholangitis, and liver
abscesses; there is also an increased risk of developing a
The differential diagnosis includes primary sclerosing cholangitis
and recurrent pyogenic cholangitis, though both of these conditions
usually cause stricturing and dilatation of both the intra-and
extrahepatic biliary tree, in contrast to Caroli's disease, which
affects only intrahepatic ducts.
Neoplastic cystic lesions
Undifferentiated embryonal sarcoma
This is a rare malignant tumor that is usually seen in teenagers
and that frequently manifests as a large, solitary, predominantly
cystic mass. The cystic appearance relates to the high water
content of the myxoid stroma.
It is usually a multiseptate lesion with a variable, predominantly
peripheral solid component. The multiseptate nature may be better
appreciated on ultrasound and MRI than on CT. MRI generally shows a
focal mass with multiple cystic spaces, septations, and central
Following contrast administration, there may be heterogenous
enhancement of the solid components of the tumor. As with all
cystic lesions, intralesional hemorrhage will alter the signal
characteristics, typically increasing the SI on T1W imaging. While
this is a rare tumor, the diagnosis should be borne in mind when a
teenage patient presents with a large, solitary cystic mass.
Biliary cystadenoma and adenocarcinoma
These are rare, slow-growing, multilocular cystic tumors derived
from biliary epithelium, although they generally do not communicate
with the biliary system.
The subepithelial stroma may be similar to ovarian or be of
Histological types include mucinous (the commonest type), serous,
and papillary. They are most frequent in middle-aged women and on
ultrasound are seen as a multiloculated cyst. CT usually reveals a
solitary, well-defined cystic lesion with a thick, fibrous capsule;
mural nodules, internal septations, and, occasionally, capsular
calcification may also be seen (Figure 4). MRI may also show
nodules and septations, which are more commonly seen in the
adenocarcinoma variety. However, neither radiology nor cytology of
cyst fluid is reliable enough to discriminate adenoma from
adenocarcinoma; thus, if this diagnosis is suspected, surgical
resection is essential.
The prognosis is good if the tumor is completely resected, but
recurrence is frequent if resection is incomplete.
Cystic subtypes of liver neoplasia
The most common primary liver tumors with cystic subtypes are
hepatocellular carcinoma (HCC) and giant cavernous hemangioma. At
imaging, HCC may appear cystic either because of necrosis or the
effects of local treatment, such as radiofrequency ablation.
Roughly 70% of patients with HCC have underlying cirrhosis,
although presentation as a multicystic mass in a non-cirrhotic
liver has been reported.
Nonetheless, this diagnosis should be considered when a cirrhotic
patient presents with a partially cystic mass. Vascular invasion is
also typical of this condition. Giant cavernous hemangioma may
rarely become cystic if it outgrows its blood supply. However, the
typical appearance of peripheral nodular enhancement following
contrast administration may well be preserved and should suggest
the diagnosis. Rare tumors reported to have presented with a
partially cystic mass at imaging include adenosarcoma
Cystic liver metastases
The liver is second only to lymph nodes as a site of metastatic
disease, and liver metastases are 20 times more common than primary
Metastases in the liver may be cystic for a variety of reasons.
Metastases that become necrotic will appear cystic at imaging,
which is most commonly seen in hypervascular metastases--for
example, from a neuroendocrine tumor or sarcoma.
Mucinous primary tumors such as colorectal or ovarian tumors
frequently give rise to cystic metastases (Figure 5). In the case
of a cystic ovarian primary tumor, metastases have been reported to
evolve into cystic lesions, even if they were initially solid.
Also, metastases may undergo cystic change with response to
treatment, which has been reported in the case of metastases from a
and a gastrointestinal stromal tumor.
On imaging, cystic liver metastases may show variable wall
thickness, and, on MRI, enhancement and fluid-fluid levels may be
Their imaging appearance will vary depending on the primary tumor
and the stage of treatment.
Infective cystic lesions
Organisms may reach the liver either from the biliary tree (ie,
secondary to ascending cholangitis), hematogenously, or because of
superinfection of necrotic tissue. The most common subtypes of
liver abscess are pyogenic and amoebic. Organisms causing pyogenic
abscess include clostridium and gram-negative bacteria, such as
. Ultrasound, CT, and MRI are all >90% sensitive for the
presence of a liver abscess,
although there is great variability in imaging appearances
depending on the stage of infection. For this reason, imageguided
aspiration, with or without drain placement for treatment, may be
necessary to make the diagnosis. A pyogenic abscess may initially
manifest as a cluster of small abscesses that coalesce into a large
abscess cavity. Ultrasound may show a variable appearance that
ranges from echogenic to anechoic
(Figure 6), while CT generally shows a uni- or multilocular cystic
lesion that may be associated with a thick enhancing wall and
(Figure 7). Gas within a cystic lesion is characteristic for an
abscess. MRI appearances are also variable, though wall enhancement
and perilesional edema are typical. Prompt diagnosis and treatment
of this condition have reduced mortality from 40% to approximately
Amoebic abscess has an imaging appearance that is similar to
that of a pyogenic abscess; however, it is generally seen in
younger patients and there may be a helpful travel history. If this
diagnosis is suspected, serology may be positive, and if confirmed,
percutaneous drainage is generally not necessary, as the abscess
responds well to antiamoebic therapy.
A hydatid cyst is caused by an infection with the eggs of the
echinococcus species of tapeworm;
is the more common type, with
causing the infection alveolar echinococcosis.
eggs reach the liver via the portal vein and give rise to a 3-layer
hydatid cyst. The outer layer is the pericyst, which consists of
compressed liver; inside this is the endocyst, a germinal layer;
and inside this is the ectocyst, a thin membrane. The imaging
appearances depend on the degree of cyst maturation. Initially, a
simple cyst is seen that may have an enhancing rim on CT and MRI;
the pericyst is typically low signal on T2W MRI.
A simple cyst on ultrasound may contain multiple mobile echogenic
foci (hydatid sand), which enables differentiation from a
congenital simple cyst. Subsequent to this, the classical imaging
appearance of daughter cysts within the mother cyst caused by
endocyst invagination may develop, giving rise to a wheel-spoke or
rosette appearance. Daughter cysts are typically of lower SI
relative to the high SI cyst matrix on T2W MRI. Peripheral
calcification may be seen in up to 50% of cysts on CT
(Figures 8 and 9). If the cyst is entirely calcified, it is usually
dead. Cysts may be complicated by rupture (in 50% to 90% of cases)
that can communicate with the biliary tree or directly into the
pleural or peritoneal cavity, and superinfection may follow cyst
rupture. The typical-and quite specific-imaging appearance of
infection is multiple small cysts with echogenic nodules on
ultrasound and a solid mass with numerous small (<1 cm) cysts on
CT and MRI.
Miscellaneous cystic lesions
Rarely, pancreatitis may cause the development of a pseudocyst
in the liver, usually in the left lobe. This diagnosis is suggested
by both the patient's medical history and the imaging features of
pancreatitis. MRI is the optimal imaging modality to distinguish
pseudocyst contents such as hemorrhage and debris, although
intralesional hemorrhage may cause an increase in the attenuation
on CT. These fluid collections usually become better defined with
A hematoma in the liver may be due to surgery, trauma, or a
bleed from a liver lesion. In cases caused by surgery or trauma,
the diagnosis should readily be suggested by the clinical history.
The most common liver lesions that bleed spontaneously are an HCC
and an adenoma.
Areas of focal nodular hyperplasia, metastases, or hemangiomata
very rarely bleed. As with hemorrhage anywhere in the body, the
imaging appearances vary depending on the chronicity. For example,
a subacute hematoma may have increased SI on T1W MRI because of the
paramagnetic effects of methemoglobin. After approximately 10 days,
a hematoma is usually of fluid attenuation and has the imaging
appearance of a cystic lesion.
Biloma occurs because of rupture of the biliary system, which
may be caused by either surgery or trauma or may occur
spontaneously. It may be intra- or perihepatic and is generally
seen near the porta hepatis or gallbladder fossa. Bile causes an
intense inflammatory response that leads to the development of a
pseudo-capsule. Imaging shows a cystic lesion that may contain
debris but rarely has septations or calcification
(Figure 11). The diagnosis may be suggested by the clinical
history. Cholescintigraphy may confirm communication of the fluid
collection with the biliary tree. The liver-specific contrast agent
mangafodipir trisodium (Teslascan, GE Healthcare, Princeton, NJ) is
excreted via the biliary system and T1W MRI after injection of this
agent may be useful in the diagnosis of a bile leak.
There are many causes of cystic liver lesions with a huge
variability of clinical significance attached to them. Awareness of
the clinical history is always useful in narrowing the differential
diagnosis. However, given the regularity with which these lesions
are encountered in everyday practice and their often nonspecific
clinical presentations, it is also essential for radiologists to be
armed with knowledge of the key imaging features of the more
important lesions. Avoiding the need for aspiration or biopsy, if
at all possible, must be a primary goal for the radiologist.