Biopsy-Proven Hepatic Extramedullary Hematopoiesis With Chronic Portal Vein Thrombosis in JAK2 V617F-Positive Prefibrotic Myelofibrosis: Contributors to Noncirrhotic Portal Hypertension.

Noncirrhotic portal hypertension warrants evaluation for vascular and infiltrative etiologies when hepatic fibrosis is absent. We describe a 48-year-old man with JAK2 V617F-positive prefibrotic primary myelofibrosis who developed chronic portal vein thrombosis with cavernous transformation and gastroesophageal varices despite preserved liver stiffness (4.2 kPa). Endoscopic ultrasound-guided liver biopsy demonstrated grade 2 hepatic extramedullary hematopoiesis (4 foci across 10 high-power fields) without fibrosis. Chronic portal vein thrombosis was the principal driver of portal hypertension. This case demonstrates that appreciable hepatic extramedullary hematopoiesis can occur in prefibrotic primary myelofibrosis despite minimal marrow fibrosis, representing a possible intrahepatic contributor to noncirrhotic portal hypertension.