treatment is to recognize the abdominal mass that requires urgent evaluation and treatment CLINICAL PEARLS AND PITFALLS Two-thirds of abdominal masses in the neonate are renal in origin Infants with suspected renal masses should be monitored for hypertension Renal Masses Renal lesions are the most common causes of abdominal masses in the neonate Cystic masses typically represent hydronephrosis, multicystic dysplasia, or polycystic disease Solid masses include renal vein thrombosis, renal ectopic kidney, or horseshoe kidney Rarely, renal masses may represent malignant disease such as mesoblastic nephroma or Wilms tumor Depending on the size of the mass, some infants may develop feeding intolerance or respiratory distress in the setting of profound abdominal distention Infants with renal masses should be monitored closely for hypertension, as most causes of hypertension in the neonate are renal in origin Evaluation should include US to distinguish cystic from solid lesions, as well as serum testing for renal function evaluation Infants with hydronephrosis may also require voiding cystourethrogram to assess for comorbid VUR Hepatic Masses Hepatic masses in the neonate are extraordinarily rare, and can represent significant pathology Masses may include congenital hemangiomas, hepatic mesenchymal hamartomas, hemangioendotheliomas, or hepatoblastoma Because of the vascular nature of the liver and the relative immaturity of the hepatic capsule, rapidly enlarging or vascular lesions are prone to bleeding, which when present can result in significant hemorrhage This can result in severe anemia and heart failure, as well as thrombocytopenia caused by consumptive coagulopathy Patients with palpable hepatic masses should undergo additional diagnostic testing with US, as well as serum testing for complete blood count, liver function tests, coagulation studies, and alpha-fetoprotein Adrenal Masses Suprarenal masses most often represent adrenal hemorrhage, but can also represent adrenal neuroblastoma or teratoma Subclinical adrenal hemorrhage is