The differential for poorly defined centrilobular nodules includes hypersensitivity pneumonitis, RBILD, pulmonary capillary hemangiomatosis (these are the classic three causes), vasculitis (DAH) (or possibly endovascular metastasis, excipient lung disease, Langerhans cell histiocytosis – these are often associated with better defined nodules or in the case of endovascular metastases with some enlargement of the arteriole extending to the area).