Pathology Atlas

Hepatic hemangioma is the most common benign liver tumor. It originates from vascular endothelial cells and is more common in women. Most are asymptomatic and discovered incidentally. Characteristic peripheral nodular enhancement with centripetal fill-in pattern, combined with the 'light bulb sign' on T2-weighted MRI, is diagnostic.

Simple hepatic cyst is the most common incidental liver lesion. They are unilocular cysts lined by biliary epithelium containing serous fluid. More common in women and prevalence increases with age. Shows no enhancement, no wall thickening, and no solid component.

Focal nodular hyperplasia (FNH) is the second most common benign liver tumor after hemangioma. More common in young women (age 20-40). Central scar and spoke-wheel vascular pattern are characteristic. Hepatobiliary phase (HBP) hyperintensity is pathognomonic for FNH because the lesion contains functioning hepatocytes and bile ductules.

Hepatic adenoma is an uncommon benign liver tumor associated with oral contraceptive (OCP) use. Occurs in young women (age 20-40). The Bordeaux classification identifies 4 subtypes: HNF1α-inactivated (steatotic), inflammatory, β-catenin mutated (highest malignant potential), and unclassified. Clinically significant due to hemorrhage risk, and surgery is considered for large lesions.

Focal steatosis is localized fat deposition in the liver and is not a true lesion (pseudolesion). Associated with metabolic syndrome, obesity, diabetes, and alcohol use. Typical locations include segment 4, adjacent to falciform ligament, and gallbladder fossa. Vessels pass through normally and there is no mass effect.

Focal sparing is an area of normal (fat-free) liver parenchyma within a diffusely fatty liver. It is not a true lesion but a pseudolesion. Most commonly seen in segment 4 near the gallbladder fossa and around the falciform ligament. These locations are explained by aberrant venous drainage.

Biliary hamartomas (Von Meyenburg complexes) are benign developmental lesions arising from ductal plate malformation. They typically present as multiple, small (<15 mm) cystic lesions scattered throughout the liver parenchyma. Discovered incidentally and have no clinical significance. Reported prevalence up to 5.6% in autopsy series.

Regenerative nodules are benign nodules arising from hepatocyte regeneration in the cirrhotic liver. They consist of normal or near-normal hepatocytes surrounded by fibrous septa. Unlike dysplastic nodules, they carry no pre-malignant potential. Siderotic nodules appear hypointense on both T1 and T2 due to iron deposition.

Pyogenic liver abscess is a focal hepatic lesion resulting from bacterial infection, typically of biliary or portal venous origin. Most common organisms include E. coli, Klebsiella, and Streptococcus species. Fever, leukocytosis, and right upper quadrant pain are typical clinical findings. The 'cluster sign' describes the tendency of small abscesses to coalesce into a single large cavity.

Amebic abscess results from Entamoeba histolytica reaching the liver via the portal venous system. It occurs more frequently in young males and typically presents as a single, large cavity in the right lobe. The content consists of necrotic material with an 'anchovy paste' consistency. Travel history to endemic areas is important for diagnosis.

Hydatid cyst is a cystic lesion caused by Echinococcus granulosus parasite in the liver. It is common in endemic regions (pastoral areas). Staged according to WHO-IWGE classification from CE1-CE5: CE1 (simple cyst), CE2 (daughter cysts), CE3 (membrane detachment), CE4 (heterogeneous solid appearance), CE5 (calcified-inactive). Daughter cysts and floating membranes are pathognomonic.

Giant hemangioma (cavernous hemangioma >5 cm) is the most common benign vascular tumor of the liver. It differs from standard hemangioma by size (>5 cm), heterogeneous appearance due to central fibrosis/thrombosis, and very slow fill-in pattern. Complete fill-in may not occur (incomplete fill-in). It can rarely present with Kasabach-Merritt syndrome (consumptive coagulopathy).

Hepatic angiomyolipoma (AML) is a rare benign mesenchymal tumor composed of fat, smooth muscle, and abnormal blood vessels. It belongs to the PEComa family. It can be associated with tuberous sclerosis complex (sporadic cases are more common). The presence of macroscopic fat within the lesion (-20 to -100 HU) is the most important diagnostic clue. Signal loss in the fat component on opposed-phase MRI and fat-suppressed sequences is characteristic.

Hepatic inflammatory pseudotumor (IPT) is a rare benign lesion composed of chronic inflammatory cells, fibroblasts, and myofibroblasts. It can mimic malignancy (especially cholangiocarcinoma) and definitive diagnosis usually requires biopsy or resection. It may be associated with IgG4-related disease. Imaging findings are nonspecific but tend to show progressive delayed enhancement.

Hepatocellular carcinoma (HCC) is the most common primary hepatic malignancy, typically arising in the setting of chronic liver disease and cirrhosis. LI-RADS major features include arterial phase hyperenhancement (APHE), washout, enhancing capsule, and threshold growth. Portal vein tumor thrombus indicates advanced disease.

Intrahepatic cholangiocarcinoma (ICC) is the second most common primary hepatic malignancy, arising from bile duct epithelium. It characteristically shows peripheral rim enhancement with progressive centripetal fill-in on delayed phases. Capsular retraction and biliary dilatation are important ancillary findings. Primary sclerosing cholangitis (PSC) is the most significant risk factor.

Combined hepatocellular-cholangiocarcinoma (cHCC-CCA) is a rare primary liver malignancy containing both HCC and ICC components. Imaging features are variable and may show characteristics of both tumors. Definitive diagnosis is usually made at pathology. It may arise in the setting of cirrhosis.

Fibrolamellar HCC is a rare primary hepatic malignancy occurring in young patients (10-35 years) in non-cirrhotic liver. It presents as a large, heterogeneous, well-defined mass. A calcified central scar is the characteristic finding. AFP is not elevated. It demonstrates a distinct clinical and radiological profile from conventional HCC.

Hepatoblastoma is the most common pediatric hepatic malignancy, typically presenting in children under 3 years of age. It appears as a large, heterogeneous, well-defined mass. Calcification is common. AFP levels are markedly elevated. It is associated with Beckwith-Wiedemann syndrome and familial adenomatous polyposis.

Neuroendocrine tumor (NET) liver metastasis is one of the most common causes of hypervascular metastases. The primary tumor usually originates from the gastrointestinal tract or pancreas. It shows marked arterial phase enhancement and may mimic HCC. Multiple, well-defined lesions are typical. Carcinoid syndrome may accompany.

Breast cancer liver metastasis is one of the most common sites of visceral metastasis from breast cancer. It typically presents as multiple hypovascular lesions. Rim enhancement and diffusion restriction are typical findings. Enhancement pattern may vary by breast cancer subtype (HR+, HER2+, triple-negative).

Melanoma liver metastasis is a metastasis type with characteristic MRI signal features due to melanin content. T1 hyperintensity (paramagnetic effect of melanin) and T2 hypointensity are pathognomonic findings. Amelanotic melanoma metastases may not show these typical signal characteristics. Known melanoma history is key diagnostic information.

Renal cell carcinoma (RCC) liver metastasis belongs to the hypervascular metastasis group. RCC tends to metastasize late and may appear years after nephrectomy. It shows marked arterial enhancement and may mimic HCC or other hypervascular lesions. Necrosis and hemorrhage are common.

Hepatic lymphoma may be primary or secondary (more common). Secondary involvement is seen in up to 50% of systemic lymphomas. It can present in diffuse/infiltrative or nodular forms. Typically seen as mildly enhancing hypodense lesions with marked diffusion restriction on DWI. Known lymphoma history and hepatosplenomegaly are important diagnostic clues.

Epithelioid hemangioendothelioma is a rare, low-to-intermediate grade vascular malignancy of the liver. It occurs more commonly in young women. Lesions present as multifocal, peripheral/subcapsular, coalescent nodules with capsular retraction. The 'lollipop sign' (vessels terminating at the tumor margin) and 'target sign' are characteristic findings.

Hepatic angiosarcoma is the most common primary malignant vascular tumor of the liver. It has a highly aggressive clinical course with poor prognosis. Vinyl chloride, thorotrast, and arsenic exposure are risk factors. Intratumoral hemorrhage is characteristic. On CT/MRI, it appears as a heterogeneous mass with early peripheral enhancement and progressive fill-in.

Low-grade dysplastic nodule (LGDN) is a pre-malignant lesion found in cirrhotic liver. It falls between regenerative nodule and high-grade dysplastic nodule on the dysplasia spectrum. Usually not visible or isodense on imaging. Does not show APHE and is iso/hyperintense on hepatobiliary phase (preserved hepatocyte function). Classified as LR-3 or lower in LI-RADS.

High-grade dysplastic nodule (HGDN) is the precursor lesion to HCC in cirrhotic liver. It occupies the intermediate position between low-grade dysplastic nodule and early HCC. On MRI, T1 hyperintense, T2 iso or mildly hyperintense. May show subtle APHE but definite washout is not expected. HBP hypointensity suggests increased malignancy risk.

Siderotic nodule is a regenerative nodule containing hemosiderin (iron) in cirrhotic liver. Due to iron accumulation, it shows marked signal loss on T2 and T2* (gradient echo) MRI — this finding is pathognomonic. May appear hyperdense on CT due to iron content. It is a benign lesion but occurs in cirrhotic liver, and progression to dysplasia should be monitored.

Peliosis hepatis is a rare vascular condition characterized by blood-filled cavities within the liver parenchyma. It is associated with immunosuppression, anabolic steroid use, AIDS, and organ transplantation. Imaging findings are variable; blood pools with early or delayed enhancement may be seen. May be T1 hyperintense due to hemorrhage.