In recent years the problem of cancer of the lung has been emphasized increasingly in the medical and lay press. Programs for mass x-ray surveys and the routine use of roentgenograms of the thorax as part of the physical examination have resulted in earlier detection of thoracic neoplasms, and improved surgical techniques have made the removal of these tumors more practicable. With this emphasis on the early detection and surgical removal of thoracic tumors, it seems appropriate to call attention to an uncommon and nonsurgical cause of a circumscribed density which may appear on the roentgenogram of the thorax.
A loculated pleural effusion within an interlobar fissure can be of various shapes and sizes and can produce a density simulating a tumor or other types of disease of the lung on the roentgenogram of the thorax. These interlobar pleural effusions may be due to congestive heart failure, and, if so,