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Episode one of the Liver Tumors and Transplant chapter runs the benign masses on a single decision: imaging appearance plus hormonal or drug context usually settles the diagnosis, and biopsy enters only when the imaging is atypical or the lesion has real malignant potential. Peripheral nodular enhancement filling inward is a hemangioma, hepatobiliary-phase retention is focal nodular hyperplasia, and hepatobiliary-phase darkening is an adenoma. From the adenoma you stratify by sex, size, growth, and beta-catenin status, because that subtype is what turns a benign mass into a resection case. The two edge entities, nodular regenerative hyperplasia and peliosis hepatis, round out the pattern-recognition set.
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Welcome to Board Pearls. This is episode one of four of the Liver Tumors and Transplant chapter, in the Liver Disease module. This episode is the benign liver lesions: the benign masses and what their imaging and hormonal context tells you to do.
Start with the benign lesions, because the whole section runs on one decision: the imaging appearance plus the hormonal or drug context usually settles the diagnosis, and biopsy enters only when the imaging is atypical or when the lesion has real malignant potential. Hold that in place and each mass falls into a predictable category. Cavernous hemangioma is the most common benign liver tumor, more often in women and often multiple, and you recognize it because contrast enhances the periphery in nodular clumps during the arterial phase and then fills inward toward the center over the venous phase. That behavior comes straight from the lesion's structure, a network of wide slow-flow vascular spaces separated by thin fibrous walls, so contrast pools at the edges first because the cavernous channels admit it slowly and then works its way in, and that pattern is classical enough that you don't biopsy it.
You only treat a hemangioma when it's a giant symptomatic lesion or when it causes Kasabach-Merritt syndrome, and that syndrome is worth holding because it explains the labs on a stem: a giant or rapidly enlarging hemangioma mechanically chews up platelets and red cells and consumes fibrinogen in its abnormal vasculature, so you see thrombocytopenia, a consumptive coagulopathy, and a microangiopathic hemolytic picture. Rare high-output heart failure from large shunting is the other reason to resect or embolize. Outside those, no biopsy and no surveillance.
Focal nodular hyperplasia is the second pattern, a benign overgrowth in response to a congenital arterial malformation, again more often in women and often coexisting with hemangiomas, and its central stellate scar carries the malformed feeding artery surrounded by normal-behaving hepatocytes and working bile ductules. That last detail is the whole imaging trick. On a hepatobiliary contrast agent like gadoxetate, the functioning hepatocytes take up the contrast and the intact ductules trap it, so this lesion holds onto contrast in the hepatobiliary phase, whereas an adenoma, which has no bile ducts, goes dark in that same phase. That single difference separates the two without a needle. This lesion has no reliable link to oral contraceptives and no malignant potential, so current guidance doesn't have you stop the pill or change anything when the imaging is classical: no biopsy, no follow-up. The only exception is atypical imaging, where you biopsy to exclude adenoma or HCC in a young patient with risk factors.
Hepatic adenoma is where the thinking gets real, because here the malignant potential is genuine and it varies by molecular subtype. Adenomas occur mostly in reproductive-age women and are strongly tied to oral contraceptives, with the risk climbing steeply the longer the exposure runs, and they also associate with certain diabetes and glycogen storage disorders, polycystic ovary syndrome, obesity, and anabolic androgen use in men.
Under the microscope you see a clonal population of hepatocytes fed by naked arteries without the accompanying portal tracts or bile ducts, and there are four molecular subtypes that are the actual engine of the management decision. The inflammatory subtype is the most common. The one driven by loss of the HNF1A gene is next. The beta-catenin-activated subtype is the least common but carries the highest malignant potential, and you flag it by nuclear beta-catenin staining and glutamine synthetase on immunohistochemistry. Malignant transformation overall is uncommon but it concentrates in that beta-catenin group, and that is what drives who gets resected.
You resect any adenoma in a man regardless of size, because adenomas in men skew toward the beta-catenin subtype and transform more often, so a man with vague right-upper-quadrant fullness, a history of anabolic androgens, and a hepatic mass is a resection case whether the lesion is two centimeters or six. You also resect at five centimeters or larger, any growing lesion, any beta-catenin-positive lesion, and any that has bled, and you resect before a planned pregnancy because the hormonal surge of gestation enlarges these and raises the risk of rupture and hemoperitoneum.
Small lesions in young women on the pill can be watched, and the first move is to stop the pill, because some regress once you pull the hormonal driver, then image every six months for two years and annually after that to catch growth. Hepatic adenomatosis, meaning more than ten lesions, is a rare reason to transplant when the disease is unresectable.
Two more entities sit at the edge of this section. Nodular regenerative hyperplasia is what's behind non-cirrhotic portal hypertension when the biopsy looks deceptively normal, because the lesion is a reorganization of normal hepatocytes into tiny regenerative nodules with no bridging fibrosis, driven by vascular injury at the small intrahepatic portal venules, so the liver looks cirrhotic on imaging but the routine stain looks normal and only a reticulin stain reveals the nodular architecture without fibrosis. It associates with connective tissue disease, immunodeficiency, myeloproliferative and lymphoproliferative disorders, and the drugs azathioprine and oxaliplatin. Peliosis hepatis is the related vascular lesion, blood-filled cavities from sinusoidal endothelial injury, linked to anabolic androgens, azathioprine, oral contraceptives, and tamoxifen, and to Bartonella in HIV, and it's managed by removing the offending agent, after which the lesions regress over months.
So the benign side comes down to appearance plus context: peripheral nodular enhancement filling inward is a hemangioma, hepatobiliary-phase retention is focal nodular hyperplasia, hepatobiliary-phase darkening is an adenoma and from there you stratify by sex, size, growth, and beta-catenin status, a near-normal biopsy behind portal hypertension is nodular regenerative hyperplasia on reticulin stain, and blood-filled cavities in a drug-exposed patient is peliosis. Biopsy stays reserved for atypical features or for the adenoma decisions where the beta-catenin subtype changes everything.
The next episode turns to the malignant side, hepatocellular carcinoma, and works it from who gets surveilled through how a surveillance finding becomes a diagnosis on the imaging algorithm and how that diagnosis picks a treatment through the staging system.