Cerebral air embolism (CAE) is a rare neurologic complication that can occur in patients undergoing various medical procedures or trauma. CAE can sometimes result in death caused by severe brain edema. In spite of these implications, the pathophysiologic mechanisms and radiologic features of fatal CAE remain to be elucidated. In this case report, a patient with carcinomatous pleuritis lost consciousness and developed quadriplegia and had generalized seizures during intrathoracic lavage. Serial computed tomography (CT) revealed the presence of air in intracranial blood vessels following severe brain edema; these are typically observed on the CT scans of patients with fatal CAE. Diffusion-weighted imaging (DWI) of the brain obtained at 24 hours after the onset of CAE revealed scattered cortical gyriform high signal intensity often observed in CAE cases, whereas the apparent diffusion coefficient and T2-weighted imaging revealed diffuse hyperintensity in the subcortical deep white matter, indicating vasogenic edema. Our case showed predominant vasogenic edema rather than cortical ischemic changes in the subcortical deep white matter area. These findings indicate that diffuse subcortical vasogenic edema could be the main cause of mortality in fatal CAE.