Features on CT scan can be compatible with Bochdalek hernia which is a form of congenital diaphragmatic hernia. They occur posteriorly and are due to a defect in the posterior attachment of the diaphragm when there is a failure of pleuroperitoneal membrane closure in utero. Retroperitoneal structures may prolapse through the defect. 
Large hernias typically present in infancy, are usually are said to be most frequently left-sided. In adults, incidentally-discovered posterior diaphragmatic hernias are rare (0.17% of patients having an abdominal CT). Of these, right-sided hernias are more common (68%), and more frequent in females.