13.3 Focal Liver Lesions

Focal lesion characterization combines strict sonographic criteria with clinical history. The exam repeatedly tests the classic appearance of each entity.

Cystic Lesions

A simple hepatic cyst must satisfy four criteria: anechoic interior, thin or imperceptible wall, well-defined smooth borders, and posterior acoustic enhancement — the artifact of increased through-transmission behind fluid. It shows no internal Doppler flow. Simple cysts are common and increase in prevalence with age. A complex cyst — with septations, internal debris, thick or irregular walls, or calcification — is never dismissed as simple; the differential includes hemorrhagic cyst, abscess, cystic metastasis, biliary cystadenoma/cystadenocarcinoma, and echinococcal disease.

Benign Solid Tumors

Cavernous hemangioma is the most common benign liver tumor, more frequent in women. The typical form is a uniformly hyperechoic, well-circumscribed mass, often with posterior acoustic enhancement because its blood-filled vascular spaces transmit sound well. Flow is too slow to detect on color Doppler, so internal signal is usually absent. Atypical (often larger) hemangiomas may be heterogeneous from fibrosis and thrombosis.

Focal nodular hyperplasia (FNH) is the second most common benign tumor. It is often isoechoic to liver and detected only by contour bulge or vessel displacement; the hallmark is a central fibrous scar with a spoke-wheel arterial pattern on Doppler. It contains all normal hepatic elements and has no malignant potential.

Hepatic adenoma is strongly associated with oral contraceptive use and with glycogen storage disease. It is clinically important because it can hemorrhage (right upper quadrant pain, dropping hematocrit) and carries a small risk of malignant transformation, so surgical resection is often advised. Its echogenicity is variable.

Related Cystic and Benign Considerations

Polycystic liver disease presents as innumerable simple cysts replacing much of the parenchyma, frequently accompanying autosomal dominant polycystic kidney disease; each cyst still meets simple-cyst criteria, so the diagnosis rests on number and distribution rather than atypical features. A useful exam contrast: FNH is thought to be a hyperplastic response around a vascular malformation, is usually managed conservatively once characterized, and shows the central scar; adenoma is a true neoplasm of hepatocytes, is hormonally driven, and is treated more aggressively because of bleeding and transformation risk. Both occur predominantly in women of childbearing age, so the clinical history — especially oral contraceptive use — is part of the imaging differential.

Malignant Tumors

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy, arising on a background of cirrhosis or chronic hepatitis B/C. Patterns include a solitary mass, multiple nodules, or diffuse infiltration; lesions may show a mosaic architecture (nodules within a nodule) and a thin fibrous capsule. HCC has a strong tendency to invade the portal and hepatic veins — a solid, expansile thrombus with internal arterial flow in the portal vein is tumor, not bland clot. Serum alpha-fetoprotein (AFP) is elevated, with markedly high levels strongly suggestive. This is why cirrhotic patients undergo ultrasound surveillance every 6 months with AFP.

Metastases are, overall, the most common malignant lesions in the liver — roughly 20 times more frequent than primary tumors — usually from colon, breast, and lung primaries. They are typically multiple and of variable echogenicity: hyperechoic metastases are classic for colorectal primaries, while hypoechoic ones suggest lymphoma or breast. A hypoechoic halo around a solid mass (the target or bull's-eye pattern) is a suspicious malignant feature.

Infectious Masses

A pyogenic hepatic abscess presents with fever, right upper quadrant pain, and leukocytosis. Sonographically it is a complex fluid collection with thick, irregular walls, internal debris, and possibly gas — bright foci with 'dirty' shadowing or reverberation are virtually diagnostic. An amebic abscess (Entamoeba histolytica) is usually solitary, in the right lobe near the capsule.

The echinococcal (hydatid) cyst, from Echinococcus granulosus in sheep-raising regions, shows a 'cyst within a cyst' pattern with daughter cysts, detached endocyst membranes (the water lily sign), and peripheral eggshell calcification when chronic.

Differential Logic by Echogenicity

Always layer in context: cirrhosis plus a new solid mass plus rising AFP points to HCC; fever and leukocytosis point to abscess; known colon cancer points to metastasis.

Additional Exam-Worthy Distinctions

The fibrolamellar variant of HCC deserves special mention: it occurs in young adults without cirrhosis, has a better prognosis, may contain a central scar with calcification (mimicking FNH), and — importantly — does not reliably elevate AFP. For abscesses, ultrasound both diagnoses and guides percutaneous aspiration or drain placement; pyogenic abscesses are treated with antibiotics plus drainage, while uncomplicated amebic abscesses usually respond to metronidazole alone. When documenting any focal lesion, record its Couinaud segment, size in three dimensions, echogenicity relative to adjacent liver, margins, effect on vessels and capsule, and color Doppler vascularity — these descriptors are exactly what the evaluation-and-documentation portion of the blueprint expects you to know.