OBJECTIVEContinuous monitoring of jugular venous oxygen saturation (SjvO2) is useful in the management of severe head injury. Abnormally high SjvO2values can be caused by increased cerebral blood flow, decreased cerebral metabolism, brain death, contamination from extracerebral venous blood, or traumatic arteriovenous fistula.CLINICAL PRESENTATIONA 20-year-old man with severe head injury was diagnosed to have a traumatic dural carotid-cavernous sinus fistula on the day of trauma. Continuous left SjvO2monitoring from Days 4 to 12 revealed oxygen saturation ranging between 85 and 98%.INTERVENTIONSuperselective intracranial and extracranial venous sampling on Day 5 demonstrated marked regional heterogeneity in venous oxygen saturation as follows: superior sagittal sinus, 95 to 97%; straight sinus, 88%; right transverse sinus, 94%; left transverse sinus, 74%; right SjvO2, 95%; left SjvO2, 89%; the basilar plexus, 99%; right internal jugular vein, 98%; the left internal jugular vein, 94%. Extremely high oxygen saturation in the superior sagittal sinus and basilar plexus was attributed to severe brain damage and carotid-cavernous sinus fistula, respectively.CONCLUSIONAlthough jugular bulb oximetry is useful in the management of severe head injury, high oxygen saturation values should be interpreted with caution because they cannot show the intracranial heterogeneity of venous oxygen saturation.