Can hiatal hernia be missed on ct scan?

Yes.: Small hiatal hernias may not be visible. Also many hiatal hernias are "sliding" so they may not be apparent when you're laying flat on your back. The best test other than endoscopy is an upper GI series for delineating hiatal hernias.

Yes: Especially if the ct scan was done for something else. An upper GI contrast study, often referred to as an esophagram is usually very good at making this diagnosis. Hope this helps!