Nodular regenerative hyperplasia of the liver: an under-recognized cause of portal hypertension in hematological disorders.

Portal hypertension has been described in a wide variety of hematological disorders, especially myeloproliferative and lymphoproliferative disorders. Its clinical manifestations may include bleeding esophageal varices, ascites, or hepatic encephalopathy. In patients with hematological disorders, there are a number of potential causes of portal hypertension, including nodular regenerative hyperplasia of the liver (NRH). This lesion is characterized by diffuse replacement of normal hepatic parenchyma by multiple small nodules composed of regenerating hepatocytes with minimal or no fibrosis. This lack of fibrosis distinguishes NRH from cirrhosis. Unlike cirrhosis, NRH only rarely results in compromised hepatic synthetic function. The major manifestation is portal hypertension related to increased resistance to blood flow within hepatic sinusoids. NRH has been linked to a variety of systemic diseases including collagen vascular diseases, myeloproliferative and lymphoproliferative disorders, as well as various medications. Although NRH is commonly associated with blood dyscrasias, the diagnosis is overlooked because of the complexity and wide differential diagnosis of liver diseases in the setting of hematological malignancy. We review herein nodular regenerative hyperplasia of the liver, including aspects of epidemiology, pathogenesis, differential diagnosis, clinical course, and treatment. We highlight its association with different forms of hematological disease, aiming to increase the awareness of this entity to the internist and the treating hematologist/oncologist.