A 18 year-old woman presented with headaches followed by lethargy and coma. On examination, she had papilledema. To a painful stimulus, she withdrew the left side better than the right.

Axial CT scan. Note the diffuse cerebral edema manifest by effacement of the ventricles, cisterns and sulci, as well as lack of differentiation between the gray and white matter. In addition, note the mass effect of the left hemisphere on the right (better seen on the image to the right). This is the CT appearance of impending herniation. The etiology cannot be determined from this scan.