A 56-year-old woman with renal colic pain was evaluated with noncontrast CT. A small ureteropelvic junction stone was found, along with numerous cysts throughout the liver.
IMAGING MODALITY OF CHOICE
Cystic lesions of the liver are common and have several causes, loosely grouped as congenital, infectious, neoplastic, and other. The lesions can be singular or multifocal and simple or complex. Because many of these lesions overlap in their imaging appearance, the clinical history is useful to narrow down the differential diagnosis.
Various imaging modalities can be used to evaluate cystic hepatic lesions, including sonography, MDCT, and MRI with MRCP. Many lesions have classic appearances on CT and MRI, providing a definitive diagnosis. MRI with fluid-sensitive T2-weighted sequences, including MRCP, can accurately characterize these lesions as cystic, even when extremely small, and define their relationship with the biliary system. However, CT's advantages include the highest sensitivity at detecting calcifications, which is often a distinguishing feature.
Simple hepatic cysts are one of the most common incidental findings; they are sharply circumscribed, water-attenuating (%10 to 10 HU), T1 hypointense, T2 hyperintense lesions with no postcontrast enhancement. On sonography, they are anechoic fluid collections with increased posterior through transmission. No complex features such as mural modularity or wall thickening or septations are present. Simple hepatic cysts are quite common and may be singular or more often multiple and usually asymptomatic (Fig. C24.1). They can be of variable sizes. Occasionally, these can hemorrhage internally, becoming hyperdense on CT, and of variable signal intensity on MRI. Layering of serous fluid and blood products of varying age may occur, resulting in a hematocrit level. Autosomal polycystic liver disease, alone or coexisting with autosomal dominant polycystic kidney disease, will present as innumerable morphologically simple cysts or complex cysts.
Multiple hepatic cysts in the setting of ADPKD. Axial noncontrast CT shows multiple simple hepatic cysts that are well circumscribed with a low internal density equal to fluid. Also present are innumerable cysts within bilateral kidneys in this patient with autosomal dominant polycystic kidney disease (ADPKD).
Bile duct hamartomas, also known as von Meyenburg complex, are residual remnants of small interlobular embryonic bile ducts that fail to regress. They are usually asymptomatic and are incidentally found as numerous morphologically simple cystic lesions; their only distinguishing feature is that they tend to be uniformly smaller than 1.5 cm (Fig. C24.2).
Biliary duct hamartomas. MRCP image demonstrating numerous small T2 hyperintense cystic lesions; majority are less than 1.5 cm in size. They also do not communicate with the biliary tree.
Choledochal cysts are rare entities caused by embryonic ductal plate abnormalities; their appearance depends on their involvement with the intrahepatic or extrahepatic biliary system. Todani created a classification system based on which portion of the biliary tree was involved (Fig. C24.3). Most of these cysts are diagnosed during infancy, with a classic triad of abdominal pain, jaundice, and an abdominal mass; however, some may go undetected until adulthood, with variable presentations. The most common form (Todani type I) results from fusiform dilatation of the extrahepatic bile duct (Fig. C24.4). Caroli disease (Todani type V) involves the large intrahepatic ducts, which retain their communication with the biliary tree. This results in large saccular and fusiform dilatation of the intrahepatic bile ducts, which unlike the previously described multicystic diseases, communicate with the biliary tree; they are best appreciated on MRCP. Another distinguishing feature related to their embryogenesis is their relationship to the portal veins. Insufficient resorption of the embryonic duct causes it to dilate and encase the adjacent portal vein. This results in the characteristic ‘central dot’ sign seen on contrast-enhanced CT and MR examinations, representing a cystic lesion surrounding a central portal vein (Fig. C24.5). These can be of variable size, measuring up to 5 cm, and can contain calculi or sludge. Complications from biliary stagnation include recurrent bouts of cholangitis, liver abscesses, or obstructing stones, resulting in jaundice. Caroli syndrome occurs when these findings are coexistent with congenital hepatic fibrosis, which can lead to cirrhosis, portal hypertension, and an increased risk of cholangiocarcinoma.
Todani classification of choledochal cysts.
Type I: Most common variety (80%-90%) involving saccular or fusiform dilatation of a portion or entire CBD with normal intrahepatic ducts.
Type II: Isolated diverticulum protruding from the CBD.
Type III or choledochocele: Arise from dilatation of duodenal portion of CBD.
Type IV: Characterized by multiple dilatations of the intrahepatic and extrahepatic biliary tree.
Type V or Caroli's disease: Cystic dilatation of intra hepatic biliary ducts.
Type 1 choledochal cyst. Coronal CT image demonstrating a large cystic lesion (*) in the porta hepatis adjacent to the portal vein (white arrow) representing fusiform dilatation of the CBD.
Caroli's disease (Type V). Axial T2 weighted FS image showing Caroli's disease with numerous intrahepatic T2 hyperintense cystic lesions. Notice the ‘central dot’ sign (white arrow) representing the encased portal vein branches.
Mucinous cystic neoplasms, formerly known as biliary cystadenomas or cystadenocarcinomas, are considered premalignant or malignant neoplasms. They usually present in middle-aged white women, accompanied by abdominal pain, nausea, vomiting, or obstructive jaundice. They are described as complex, multilobulated cystic lesions with internal septations, mural nodularity, and a thick outer capsule, all of which may demonstrate contrast enhancement (Fig. C24.6). The density or signal intensity in the cystic portions depends on the proteinaceous content. They are grouped together because imaging cannot reliably distinguish between benign cystadenomas and malignant cystadenocarcinomas; the treatment of all these lesions is surgical resection.
Biliary cystadenoma of the liver. (A) Coronal and (B) axial CT image of a biliary cystadenoma (white arrows). Notice the complexity with internal septations. While this looks very similar in location to the earlier example of the type 1 choledochal cyst, this can be identified as an intraparenchymal lesion, using the ‘claw’ sign. This is the thin tapering rim of parenchyma visualized at the inferior margin of the mass.
Metastases to the liver are rarely cystic in nature, usually arising from primary tumors such as mucin-producing ovarian or colonic adenocarcinomas or rapidly growing tumors with central necrosis, such as sarcomas or melanoma. Treated metastases from other primary tumors can also undergo degeneration of necrosis and can result in cystic lesions. This is especially true for treated metastases from GISTs. These can occur singularly but are more commonly multiple complex cystic lesions with variable degrees of enhancement.
Infectious causes include pyogenic, amebic, and fungal abscesses. The clinical history and presentation are extremely important in differentiating these entities, which all require different treatment. These usually manifest as low-density lesions, albeit not as low as simple fluid (10-40 HU), with a thick enhancing rim. A characteristic CT finding is the ‘cluster of grapes’ sign, which represents a conglomeration of multiple small pyogenic abscesses in a large multiloculated cavity (Fig. C24.7). Intracavitary gas is also a reliable sign of a pyogenic abscess. A hydatid cyst is caused by the larval tapeworm Echinococcus granulosus. Hydatid cysts may be difficult to distinguish on imaging alone, but a clinical history of right upper quadrant pain, eosinophilia, positive serological findings, and travel to endemic areas simplifies the diagnosis. These may manifest as unilocular or multilocular cysts, occasionally with crescentic mural calcifications, small daughter cysts, and little peripheral enhancement.
Hepatic abscess. Axial CT postcontrast showing a pyogenic abscess. Notice the thick enhancing, irregular septations (white arrows). Also bilateral reactive pleural effusions.
Hematomas or bilomas may be found; however, these will often have a precedent history of trauma, surgery, or interventional procedure. A large spontaneous hematoma should raise the concern for an underlying mass, such as hepatocellular carcinoma or adenoma. Acute hematomas will be hyperdense but will gradually decrease in attenuation over time. Likewise, their MRI signal intensity will depend on the age of the blood products.
As you can see, several entities can present with cystic liver lesions. Some of these may be asymptomatic with no clinical consequence (biliary hamartomas and simple hepatic cysts). Recognizing these as benign lesions when incidentally detected is probably the most important thing to remember. When the lesions become more complex, a much wider differential exists and the clinical context will likely be the distinguishing feature. These could all present with vague right upper quadrant pain, thus imaging will be performed to exclude other acute causes of right upper quadrant pain including hepatitis, cholangitis, biliary colic, pancreatitis, pneumonia, or subdiaphragmatic abscess.
REFERENCES AND SUGGESTED READING
KJ. Cystic focal liver lesions in the adult: differential CT and MR imaging features. RadioGraphics
G. Fibropolycystic liver disease: CT and MR imaging findings. RadioGraphics