Cerebral gas embolism may be revealed by the sudden onset of unconsciousness sometimes after surgery or after diagnostic and therapeutic procedures. The clinical diagnosis may be difficult if the context is not relevant. Imaging can therefore play a crucial role in revealing the presence of intracranial gas bubbles on CT or MRI scans. This report is of a case of fatal cerebral gas embolism revealed by CT and MRI performed for deep and unexplained coma. Etiological diagnosis revealed the presence of a lung tumor invading the mediastinum, thus possibly allowing the migration of gas from the lung to the arterial cerebral circulation. A second MRI performed 8 days after the initial event with diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopic imaging (¹H-MRSI) allowed better comprehension of the pathophysiological mechanisms of cerebral injury secondary to gas embolism by showing two kinds of cerebral lesions: white-matter vasogenic edema and cytotoxic gray-matter edema.