Nodular Regenerative Hyperplasia

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 cm in size with persistent enhancement on hepatobiliary-enhanced MR

Hyperintense on T1WI (75%); iso- to hyperintense on T2WI

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

May have central scar ± perinodular “halo”

MR with hepatobiliary agents: Uptake and prolonged enhancement

– Confirms benign hepatocellular nature of lesions

With signs of underlying disease (e.g., Budd-Chiari; thrombosed hepatic veins + IVC)

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

TOP DIFFERENTIAL DIAGNOSES

• Imaging features are more diagnostic than histologic features

• Multifocal hepatocellular carcinoma

• Focal nodular hyperplasia (multiple)

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

(Right) 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 (NRH) was found. 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.

(Left) Another CT section in the same renal transplant patient shows widened hepatic fissures , suggestive of cirrhosis. Liver biopsy showed diffuse nodular regenerative hyperplasia.

(Right) 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)

Synonyms

• Nodular transformation, noncirrhotic nodulation

Definitions

• Uncommonly recognized disorder characterized by diffuse micronodular or macronodular transformation of hepatic parenchyma without fibrous septa between nodules

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

IMAGING

General Features

• Best diagnostic clue

LRNs: Multiple hypervascular nodules up to 5 cm with persistent 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 are 0.5-5 cm in diameter

• Key concepts

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

CT Findings

• NECT

Nodules are usually isoattenuating to normal liver

Diffuse low attenuation in Budd-Chiari syndrome or steatosis may result in hyperattenuation of nodules

• CECT

Diffuse nodular regenerative hyperplasia

– No focal liver masses; liver may appear normal or dysmorphic

– Signs of portal hypertension are common (> 50% of reported cases)

Splenomegaly, ascites, varices

Large regenerative nodules

– Multiple focal liver masses or nodules (2 to hundreds)

Size of nodules: 0.5-5 cm

Homogeneously hypervascular on arterial and portal venous phase imaging (no washout)

May have central scar ± perinodular hypo-/hyperdense halo

Along with signs of underlying disease (e.g., for Budd-Chiari = thrombosed hepatic veins and IVC, central hepatic hypertrophy, and peripheral atrophy)