Paradoxical cerebral air embolism is an unusual complication following insertion of a subclavian intravenous catheter. We report an ultimately fatal case in a 75-year-old man in whom the diagnosis was confirmed by computerized tomographic (CT) scanning. W e postulate that air passed through a physiologically closed but anatomically patent foramen ovale.A 75-year-old black man with an ileocutaneous fistula had an alimentation catheter inserted into the right subclavian vein while in the Trendelenburg position. After completion of the maneuver and assumption of a sitting position, the patient became unresponsive in midsentence. Neurological evaluation revealed right conjugate gaze preference with full conjugate excursion to the left upon left caloric stimulation with cold water. The patient was not responsive to verbal stimulation; noxious stimulation caused decerebrate posturing on the right. All extremities were rigid. Deep tendon reflexes were symmetrically hyperactive and plantar responses were bilaterally extensor.A chest radiograph showed neither pneumothorax nor hemothorax, and the tip of the central venous catheter lay in the region of the superior vena cava. An unenhanced brain CT scan performed o n a GE 8800 unit, employing a 1 cm collimator, reveaied multiple small, well-defined collections of markedly decreased attenuation within both cerebral hemispheres. Attenuation coefficients of the lesions were equivalent to that of air in the left frontal sinus. Presumably, the abnormalities represented intrahemispheric collections of air, probably within and around small-caliber arteries (Figure).Three hours later the patient was placed on 10056 oxygen and transferred to a monoplace hyperbaric recompression (HBR) chamber. One hundred percent oxygen given at 3 atm absolute pressure for 45 minutes elicited no improvement. H e was then transferred to a multiplace H B R chamber where the treatment protocol of the US Navy Diving Manual, Table GA, was followed [ 5 ] . N o improvement occurred, and the patient remained in a vegetative state until his death eight weeks later. CT scans performed four and six weeks postictus revealed poorly defined areas of infarction density scattered throughout both cerebral hemispheres. Investigation for the mechanism of paradoxical embolization by the indocyanine green test and the technetium 99m-labeled macroaggregated albumin test failed to show major right-to-left shunts in either the heart or lungs.Systemic air embolism is almost invariably iatrogenic ex-