FIG 3. Shunt overdrainage. Spin-echo T1-weighted image at 500/15. Following surgery for marked hydrocephalus secondary to aqueductal stenosis, the classic clinical and radiologic pictures of overdrainage were present. Note beyond normal changes of midline structures, including reversal of the mammillary body ratio. Following third ventriculostomy, with marked clinical improvement, midline structures changed in the expected direction (not shown). Encephalomalacic, including cystic, changes are present in the corpus callosum secondary to impingement. FIG 4. Marked atrophy in a case of long- standing multiple sclerosis. Spin-echo T1-weighted image at 400/12. Relations between midline structures are similar to those of normal brain