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Nodular Regenerative Hyperplasia


KEY FACTS

Terminology

  • Diffuse micro- or macronodular transformation of hepatic parenchyma without fibrous septa between nodules

  • Larger focal lesions are called multiacinar (large) regenerative nodules (LRNs)

  • Benign lesions: No potential for malignant transformation

Imaging

  • Gadoxetate (Eovist)-enhanced, multiphasic MR is best imaging test

  • Diffuse nodular regenerative hyperplasia (NRH) and focal LRNs have different etiologies and imaging features

  • Diffuse NRH

    • Associated with other diseases and drugs (e.g., myeloproliferative; immunosuppressives)

    • Signs of portal hypertension are common (> 50%)

  • LRNs

    • Multiple focal liver masses or nodules 0.5-5.0 cm with persistent enhancement on hepatobiliary-enhanced MR [Gadoxetate (Eovist, Primovist)]

    • Hypervascular on arterial, portal venous, and delayed-phase imaging ( no washout )

    • May have central scar ± perinodular halo

    • Hyperintense on T1WI (75%)

    • Isointense or hypointense nodules on T2WI

    • With signs of underlying disease (e.g., Budd-Chiari: thrombosed hepatic veins &/or inferior vena cava)

Top Differential Diagnoses

  • Imaging features are more diagnostic than histologic

  • Multifocal hepatocellular carcinoma

    • Can be differentiated by MR features and clinical setting

  • Focal nodular hyperplasia

    • Imaging and histologic features may be identical to NRH

    • Different clinical setting; FNH usually isolated lesion in healthy young woman

Axial CECT in a 52-year-old man with a renal transplant shows massive ascites and esophageal varices
.

Axial CT section of the liver in the same patient shows no evidence of fibrosis or focal lesions; liver biopsy showed no cirrhosis but diffuse nodular regenerative hyperplasia. This is a recognized cause of liver failure in the absence of cirrhosis and a known complication of solid organ transplantation, among many other etiologies.

Another CT section in the same renal transplant patient shows widened hepatic fissures
, suggestive of cirrhosis. Liver biopsy showed no cirrhosis but diffuse nodular regenerative hyperplasia.

Trichrome stain highlights the nodules
. By definition, there are no fibrous septa between the nodules in nodular regenerative hyperplasia. (Courtesy S. Kakar, MD.)

TERMINOLOGY

Abbreviations

  • Nodular regenerative hyperplasia (NRH)

  • Large regenerative nodules (LRNs)

Synonyms

  • Nodular transformation, noncirrhotic nodulation

Definitions

  • Nodular regenerative hyperplasia (NRH): Uncommonly recognized entity characterized by diffuse monoacinar (micronodular) transformation of liver parenchyma without fibrous septa between nodules

  • Large regenerative nodules (LRNs): Larger focal lesions are called multiacinar (large) regenerative nodules

  • Both NRH and LRN categorized as benign regenerative nodules

IMAGING

General Features

  • Best diagnostic clue

    • NRH: Diffuse liver lesions are often not visible at all

    • LRNs: Multiple hypervascular nodules up to 5 cm with delayed enhancement on hepatobiliary-enhanced MR

  • Location

    • Diffuse involvement; microscopic nodules predominantly distributed in periportal region

  • Size

    • Monoacinar lesions in NRH are only ~ 1 mm in diameter with clusters of lesions up to 10 mm

    • LRNs: 0.5-5.0 cm in diameter

  • Key concepts

    • Diffuse NRH and focal LRNs have different predisposing conditions and different imaging features

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