Chronic vermal herniation in a case of osteosarcoma of the occipital bone.

Upward projection of the cerebellar vermis through the tentorial hiatus is called upward vermal herniation (UVH). UVH is less common in clinical practice than uncal herniation. Even more uncommon is chronic vermal herniation and impaction in the tentorial hiatus. To illustrate this phenomenon, we present the clinical, radiological, and morphological features of vermal impaction in a patient with a postradiation osteosarcoma of the occipital bone. In spite of nearly total excision of the tumor pushing the cerebellum upward, his postoperative course was complicated by respiratory problems and an altered level of consciousness, finally resulting in death. His clinical status paralleled the computed tomographic (CT) demonstration of persistent obliteration of the supramesencephalic cistern. CT makes more reliable the detection and management of UVH, but a high index of suspicion is necessary for prevention of this complication.