Now that we have your attention - let's talk about liver ultrasound. A topic that we do not deal with often in the ER setting, but due to all of those FAST exams and RUQ studies that we do, it's important to be able to recognize when the liver isn't normal!
And now, onto....
The Basics of Liver Ultrasound
The liver is a large solid vascular organ that is best visualized with a curvilinear transducer with a (low) frequency between 2-5 MHz. The patient can be examined in a supine position with normal respirations. The normal liver has a homogenous echogenic appearance. Any heterogenous appearance should be concerning for pathology. Here are a few non-traumatic pathologies to be aware of during your scanning.
- Simple cysts are considered the most common focal liver lesion. They are anechoic with increased through transmission, and a well-defined back wall.
- Complex cysts are identified by internal echoes, a thick wall, septations that are numerous or thick, solid elements, or calcification and are most often due to hemorrhage
- Vascular lesions such as aneurysms, arterioportal fistulas, and portal hepatic vein fistulas can simulate cysts on gray-scale sonography but are easily distinguished with Doppler analysis
- The most common benign liver neoplasm found most commonly in women.. They are classified by multiple, small, blood-filled spaces are separated by fibrous septations and lined by endothelial cells that typically do not bleed or cause symptoms. Therefore, they are usually an incidental finding on ultrasound.
- They are defined by sharp and smooth margins that may be round or slightly lobulated.
- Only 2% of hemangiomas enlarge on follow-up scans and they usually remain stable overtime. If the patient does not have chronic liver disease or risk of malignancy, a homogeneous hyperechoic liver lesion requires no further evaluation.
Focal nodular hyperplasia (FNH):
- A benign tumor of the liver that is composed of Kupffer cells, hepatocytes, and biliary structures. FNH is usually detected as an incidental mass.
- On ultrasound, most FNHs are isoechoic to liver parenchyma
- Unlike hepatic adenomas, they are not related to birth control pills, although birth control pills may promote their growth. They seldom bleed or cause any clinical symptoms, although pain may be encountered when the lesions are large.
- The differential diagnosis of FNH includes fibrolamellar carcinoma, hepatic adenoma, HCC, hemangioma, and vascular metastases.
- Adenomas are rare benign tumors that contain normal (or occasionally slightly abnormal) hepatocytes but few Kupffer cells and virtually no bile ductules. Adenomas occur most commonly in patients taking birth control pills or anabolic steroids.
- Their propensity to bleed makes them surgical lesions despite their benign histology. They also have a low but real risk of malignant degeneration.
- Simple, small uncomplicated adenomas tend to be homogeneous, varied and nonspecific. In most cases additional imaging is necessary to confirm the diagnosis.
- The lungs and liver are the most frequent sites of distant metastatic disease and usually involve both lobes of the liver.
- Liver function tests are unreliable in detecting liver metastases.
- Metastatic lesions have a target appearance with an echogenic or isoechoic center and a hypoechoic halo while thick halos represent proliferating tumor.
- CT and MRI are also helpful in confirming suspected diffuse metastases. In many clinical situations when metastatic disease is suspected biopsy is required for diagnosis.
- HCC is the most common primary malignancy of the liver.
- The growth pattern of HCC is quite variable: it may be solitary, multifocal, or diffuse and infiltrating. A typical pattern of HCC is a large dominant lesion with scattered smaller satellite lesions.
- Most HCCs are hypervascular and variable; however, this is not always evident on Doppler, particularly in deep lesions.
- Any solid mass detected on an initial sonogram in a patient with cirrhosis should be considered malignant until proved otherwise
Middleton WD, Kurtz AB, Hertzberg BS. Ultrasound: The Requisites. 2nd ed. Philadelphia, PA: Elsevier, Inc; 2016.