Liver Region Pathology
Description and examples of the important abnormalities in the liver region that the advanced IMBUS provider should identify.
DIFFUSE LIVER DISEASE
Hepatic congestion: Elevation of right heart pressure from any cause, or thrombosis of the hepatic veins (HV) (Budd-Chiari), will lead to congestion of blood in the liver. This leads to widening of the HV and hepatomegaly with a reduced echogenicity of the parenchyma. The confluence of the HV with the IVC can resemble a “bunny” as the structures enlarge. Pleural effusions and ascites may be seen in such patients. Color flow Doppler (Color) can determine whether there is flow in the HV and regurgitant flow from tricuspid regurgitation may be seen. Chronic thrombosis in HV usually is seen as an echogenic area in a vein that obstructs flow. The following is an example of elevated right atrial pressure from tricuspid regurgitation leading to dilated IVC and HVs that resembles a bunny. The Color refluxes into the HVs with RV systole.
Hepatic steatosis (fatty liver): This is common and can be alcoholic or non-alcoholic (NAFLD). Chronic viral hepatitis may also show steatosis. The NAFLD variety is seen in obesity, diabetes, and dyslipidemic patients. Many patients are asymptomatic, but the condition can damage the liver and hepatomegaly is seen in more severe cases. The diagnosis requires a comparison of the liver parenchyma with normal kidney parenchyma in the same view. This can be done in the subcostal views or in an anterolateral intercostal view. The following is NAFLD in a longitudinal subcostal view with the liver enlarged caudad of the right kidney.
A fatty liver appears brighter than normal, assuming the gain has been set correctly, but more importantly, the liver is definitely more echogenic than the kidney parenchyma. Severe steatosis reduces ultrasound penetration so the view of other liver structures may be compromised. Here is another young man with NAFLD.
A fatty liver can have focal hypoechoic areas (FHA) which are parts of the liver spared from the fatty infiltration. They are most common near the gallbladder and anterior to the portal vein. The problem with these areas is that they can suggest tumor, but they are usually not nodular in shape and the location helps with the diagnosis. The architecture shouldn’t change with such lesions and hepatic and portal veins should not be displaced. Short term follow-up with IMBUS is appropriate for equivocal cases, but MR is the definitive test to establish fat as the cause.
Unfortunately, some patients can have very prominent FHAs that are more alarming, such as the following clinic patient who required several months of followup to show no change. Large FHAs correlate with more severe steatosis.
Hepatic cirrhosis: The etiology of cirrhosis can’t be determined by IMBUS findings. Advanced cases with prominent ascites and a shrunken liver with irregular borders are easy to identify. Earlier disease requires more careful attention to the liver contour, looking for subtle irregularity. The liver can be enlarged in early cirrhosis and ascites may not be present. The liver parenchyma becomes inhomogeneous (irregular) as cirrhosis progresses and the HV become compressed. In contrast, the main PVs will become enlarged to greater than 12 mm in diameter as portal hypertension progresses. The following image shows a small amount of ascites at the top, an irregular liver contour, and some inhomogeneity of the liver parenchyma.
FOCAL LIVER LESIONS
The following overall guidelines adhere to the recommendations from the American College of Radiology. More detail about a few specific focal lesions is presented afterwards.
Low Risk Patients: less than 40 years old, no known malignancy, no symptoms attributable to the liver, no known liver dysfunction, and no known disease with an increased risk of liver malignancy.
Pure, simple cysts will be benign and do not need additional care.
Strongly hyperechoic lesions with smooth borders in a low risk patient, particularly a woman, are highly likely to be hemangiomas and these should be followed in several months with IMBUS to verify no change. No formal imaging is then needed. Periodic follow up is not recommended but nothing would be lost with periodic IMBUS surveillance as part of a periodic health visit.
All other liver lesions are problematic once they are greater than 0.5 cm in size. All of the criteria for risk of malignancy, which dictate the next steps in care, are based on CT findings.
In low risk patients, single lesions under 0.5 cm are likely benign and biopsy is not performed on this size lesion anyway. Intermittent IMBUS follow up over the next 6-12 months will verify whether the size is changing. When the size is greater than or equal to 0.5 cm, it is time for a CT.
In higher risk patients, more caution is necessary. Multiple lesions less than 0.5 cm can be metastatic disease. Even a single small lesion could be an early malignancy. The possibility of performing a PET/CT arises with these patients so consultation with radiology may be needed before ordering a CT.
Hemangioma: These lesions are common, benign, often multiple, and more often seen in women because female sex hormones are associated with development. They are usually asymptomatic and incidental, but can rarely cause troubles if they are large. Hemangiomas are hyperechoic with smooth borders that look like a “snowball” in the liver. Because they are filled with blood vessels they can give slight posterior acoustic enhancement. Hemangiomas occasionally are less hyperechoic and then CT/MR is usually needed to distinguish them from more dangerous lesions. Here is a typical hemangioma with subtle posterior acoustic enhancement.
Here is another larger hyperechoic lesion that was confirmed to be a hemangioma.
Cysts: These are common, benign, and single or multiple. With the gain set correctly these are anechoic, round or oval structures with a smooth outline. They should have posterior acoustic enhancement and may have lateral shadowing (edge artifacts). It is always a good idea to use Color or power Doppler to show that there is no blood flow in these structures. Here is a clip from a patient with multiple liver cysts, some of which were large. The cyst in this clip is completely anechoic with strong posterior acoustic enhancement and slight edge artifacts. Make sure that each cyst meets all the criteria for a simple cyst!
Next is a patient with known polycystic kidney disease. The liver showed multiple large and small simple cysts. The dominant cyst in this clip had edge artifacts and posterior acoustic enhancement.
In contrast, the next patient had a newly seen liver cyst that had some internal hyperechoic septations that could not meet the criteria for a simple cyst. This patient needed interval followup and likely formal imaging.
Focal nodular hyperplasia: This is an unusual lesion seen more often in women, but female sex hormones are not clearly associated with development. It is usually asymptomatic. The area is irregular in echogenicity and sometimes large. Color/power Doppler may show a small central artery. Unfortunately, malignancy is also a consideration with these lesions and CT/MR may be needed to differentiate them. Here is an ill-defined focal nodular hyperplasia lesion.
The following is a larger, more well defined FNH lesion with greater concern for malignancy.
Hepatocellular carcinoma (HCC): HCC occurs mostly in patients with certain types of chronic liver disease. Even if patients are being routinely screened with formal US for HCC, they might be seen in clinic with right upper quadrant complaints in between screenings and something could be seen. The lesions can be hypoechoic or hyperechoic, but are usually irregular areas. They are not as well defined as focal nodular hyperplasia. CT/MR is needed with this lesion. Here is a large and characteristically non-homogenous HCC.
This second HCC image shows two smaller lesions on the left, one of which is more hypoechoic and the other more hyperechoic.
Metastasis: These are usually multiple, variably sized, hypoechoic, non-homogenous, and without clear margins. A hypoechoic halo is a sign of malignancy. The following image shows multiple metastasis.
Gallbladder enlargement: Extended fasting produces the largest normal gallbladder (GB), which can be 10 cm in length and 4 cm in width for a normal sized adult. The main cause of a GB larger than this is distal common bile duct (CBD) obstruction, including a tumor in the head of the pancreas. Here is a GB that was enlarged by eyeball and measurement. The cause was a distal CBD cholangiocarcinoma.
Gallstones: Some gallstones can be missed by CT because they are isodense to bile. IMBUS will not miss these stones. Large gallstones are easy to see but posterior shadowing is not always easy to see without adjustments to the gain. Here is an example.
Smaller gallstones, particularly those in the neck of the GB are a concern. The acronym S-I-N (for stone in the neck) reflects the difficulty of detecting these stones and the adverse consequences of missing them. For any gallstone, particularly in the neck, the posterior acoustic shadow can be the key finding. If the patient is not overly obese and there is uncertainty about a shadow, decrease the gain and the shadow may become more distinct. In general, gallstones should move with patient movement, but stones stuck in the neck may not move. Here is a gallstone in the neck of a GB that a CT scan could not differentiate from a polyp. The shadowing is obvious with ultrasound and this frail patient needed a choecystostomy tube.
Other hyperechoic structures in the GB: Not every hyperechoic structure in a GB is a stone. Air can rarely get in the GB, but it rises to the top wall, with echogenic shadows coming off from the top. Polyps are hyperechoic, don’t move with position change, and don’t cause shadows. Here is a small polyp defying gravity on the anterior wall and casting no shadow. Movement of the patient also didn’t move this polyp.
Structures that look like polyps in the GB fundus, but have a short comet tail below them, may be adenomyomatosis, a common degenerative/hyperplastic condition of the GB that isn’t an issue itself, but it seems to accompany chronic GB inflammation. The GB wall may be thickened. This condition is fairly common in older patients and occasionally raises the possibility of GB carcinoma but the comet tails make this a benign lesion. Here is an example.
Sludge can show as hyperechoic to the bile, but usually doesn't cause posterior acoustic shadows. A GB may be filled with sludge and be almost isoechoic with the liver, thus resembling a mass at the inferior liver. However, the wall of the GB will still be there. Rarely, what looks like sludge in the GB turns out to be carcinoma so consider all the clinical features of the patient. Here is a GB mostly full of sludge.
This is another patient with more subtle GB sludge. The gallbladder wall is upper limits of normal with a normal structure. The middle hypoechoic layer is not pericholecystic fluid as discussed just below.
W-E-S Sign: The abbreviation stands for Wall-Echo-Shadow and refers to the situation of a GB collapsed around a good number of stones. There is a hyperechoic anterior wall, a thin hypoechoic layer representing the small residual lumen of the GB, and the hyperechoic beginning of the stones, below which is a very distinct posterior shadow. This is distinguished from a duodenum by noting that the outer layer of a duodenum is hypoechoic and the shadow is “dirty” with B-lines coming off periodically from duodenal contents. Here is a WES sign.
Porcelain GB:This is rare and associated with carcinoma of the GB. Superficially it can resemble a WES sign but what is present is calcification of the GB wall. This creates a thin, calcified outer wall with a posterior shadow. There is no hypoechoic middle layer or a thicker beginning stone layer. Here is an example of a porcelain GB. Optimization of this image was probably needed to be sure it wasn’t a WES sign.
Cholecystitis: In the clinic setting, acalculous cholecystitis is rarely an issue, so the absence of gallstones or sludge makes cholecystitis extremely unlikely. If stones or sludge are present, carefully measure the thickness of the anterior GB wall interfacing the liver (short or long axis). Use an optimized GB image. As mentioned in the previous chapter, don’t measure a contracted GB wall. Normal wall thickness is less than 5 mm. In a thickened GB wall, there should be several layers with the outer layer hyperechoic. The hypoechoic middle layer is not pericholecystic fluid. Pericholecystic fluid is rare and would be beyond the outer wall of the GB. A thickened GB occurs in conditions other than cholecystitis (ascites, elevated right atrial pressure, and adenomyomatosis). Here is a GB wall that was thickened by eyeball and by measurement and was associated with stones, sludge, and active cholecystitis.
Murphy sign: To perform the sonographic Murphy sign correctly, find the GB in a transverse subcostal view and position the probe lightly on the fundus of the GB. Then have the patient inspire deeply while steady pressure is maintained on the probe. Observe the degree of patient discomfort with this maneuver. Then, move the probe a little to each side of the GB and repeat the inspiration and pressure, assessing the pain again. A positive sonographic Murphy sign is pain that is increased with inspiration specifically where the GB is lying.
BILE DUCT PATHOLOGY
Studies show that evaluation of the bile ducts is of little use for diagnosis of patients suspected of subacute or acute cholecystitis. However, patients with more chronic symptoms could have obstruction of the common bile duct (CBD) or intrahepatic ducts and both the proximal and distal bile ducts should be imaged.
Common bile duct: A normal distal common bile duct (CBD) is < 6 mm in diameter but it gains 1 mm per decade in older patients and may be up to 10 mm in post-cholecystectomy patients. Normal CBDs were shown in the Liver imaging chapter.
The following clip demonstrates both dilated CBD and more proximal hepatic ducts, but requires careful examination. In the center of the image is the portal vein (PV). Posterior to the PV is a hypoechoic tube that can be seen as the continuation from some tubes out at 9:00. This tube is the CBD heading toward the pancreas. This is the same patient shown above with the enlarged GB who was eventually diagnosed with a CBD cholangiocarcinoma. Both the CBD and intrahepatic ducts are expected to be dilated in this condition. A patient with sclerosing cholangitis or a proximal cholangiocarcinoma might only have dilation of hepatic ducts with a normal size CBD.