Focal nodular hyperplasia (FNH)

What it means

This is a benign liver lesion made up entirely of normal liver cells that have organized themselves into a well-defined nodule, arranged around a central scar with blood vessels radiating outward like spokes on a wheel. Despite looking like a mass, it is not a tumor in the cancerous sense — it is thought to form as a local reaction to a small abnormality in blood flow, causing an otherwise healthy patch of liver tissue to grow into a distinct lump.

Why it appears on a CT or MRI report

This lesion is usually found by chance on a scan done for an unrelated reason, since it rarely causes symptoms. On contrast-enhanced CT or MRI, it has a fairly recognizable pattern: it lights up brightly and evenly during the early phase after contrast injection, then fades back to blend in with normal liver tissue, often with a central scar that enhances later than the rest of the lesion. This specific pattern is what allows radiologists to diagnose it confidently from imaging alone in most cases, without needing a biopsy.

What it usually means

This is the second most common benign liver lesion after simple cysts and hemangiomas, and it is found far more often in women between their twenties and forties, though it can occur in men and at other ages too. It does not carry any risk of turning into liver cancer, does not usually grow over time, and rarely causes bleeding or rupture, unlike some other liver lesions. Because its imaging appearance can occasionally overlap with other liver lesions, especially in atypical cases, radiologists sometimes recommend a follow-up scan or, less often, an MRI with a liver-specific contrast agent to confirm the diagnosis with more certainty.

When to follow up

When the imaging pattern is classic and the lesion is small and asymptomatic, most doctors recommend no treatment and no ongoing surveillance beyond routine care — this differs from some other liver masses that need regular monitoring. Discuss the report with your doctor to confirm the diagnosis is considered typical rather than indeterminate, since atypical cases may need an additional MRI or specialist review. New or worsening pain in the right upper belly, or a lesion that grows on a follow-up scan, are reasons to seek further evaluation.

A plain-language way to picture it

Imagine a small patch of a well-tended garden where the soil happens to be a little richer, causing the grass there to grow slightly thicker and greener than the lawn around it. It's still the same grass, growing in its usual way — just a bit more of it, concentrated in one spot because of the local conditions. This lesion is much the same: normal liver tissue, arranged into a noticeable lump, but functioning like the ordinary liver around it.