JAK2 and Splenomegaly: Portal vein thrombosis is an uncommon but serious complication of MPNs, which can lead to significant sequelae such as portal hypertension, splenomegaly, and the development of extensive collateral circulation. The identification of the JAK2 V617F mutation was instrumental in determining the underlying cause of the patient's hypercoagulable state, which allowed for the appropriate therapeutic interventions.