SINCE the introduction of "retropneumoperitoneum" as a diagnostic roentgenologic procedure by Ruiz Rivas in 1947, this technique has found immediate international acceptance.* In many countries, articles have been written describing the usefulness of the technique, but very little has been said about its limitations in the diagnosis of the various types of lesions that are demonstrated. All authors agree that the procedure is relatively harmless. The possibility of producing an air embolus has been recognized, and at least one case of a nonfatal air embolus has been reported.
This report is an attempt to evaluate some of these considerations and to formulate certain criteria that would be useful in the diagnosis of retroperitoneal tumors The technique used in injecting the gas into the extraperitoneal tissues has been described in detail in previous publications and will not be repeated here. Briefly, it consists of injecting a gas, preferably oxygen, into the