What imaging hallmark distinguishes focal nodular hyperplasia?

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The hallmark is a central scar with radiating (“spoke-wheel”) vessels, plus arterial-phase hyperemia that persists into the portal venous and delayed phases. This pattern occurs because FNH is a hypervascular lesion with feeding arteries producing rapid, uniform enhancement, while the central scar (fibrous tissue) often enhances more slowly on delayed imaging. This combination distinguishes FNH from other lesions: hemangioma shows peripheral nodular enhancement with progressive fill-in; malignant lesions like HCC commonly show washout in delayed phases; and lesions with a target sign or central necrosis point to abscesses or necrotic tumors rather than FNH.