Perihilar Coarsening (also known as subpleural basilar pulmonary vein enlargement) is a radiographic pattern of lung parenchymal abnormality characterized by extension of air-filled vessels into the perihilar interstitium, creating a lobular pattern. It is typically seen on computed tomography imaging of the lungs and is thought to be caused by confluent peribronchi wall changes or diffuse interstitial or fibrotic changes that reduce terminal bronchiole diameter. This conditio is associated with various causes, most commonly being long-standing dermatomyositis and idiopathic pulmonary fibrosis, but can also be caused by chronic infection, radiation therapy, or interstitial lung disease due to other causes. The radiologic pattern of perihilar coarsening may also be seen in acute respiratory distress syndrome (ARDS). Care must be taken to distinguish the pattern seen in ARDS from other causes as management of the condition depends on accurate diagnosis of the underlying cause.