Toward a Better Understanding of Normal Pressure Hydrocephalus

I read with interest the commentary and exten-sive literature review published by Bradley (1), but wish to reply to some of the comments made re-garding my article on normal pressure hydroceph-alus (NPH) (2). I will discuss the comments made regarding control selection, cardiac gating, and the selective measurement of the superior sagittal and straight sinus flow as well as those regarding the cause of the venous compression and the physiol-ogy of CSF aqueduct flow. The selection of a non-biased control group is important. The problem with investigating patients in their seventh and eighth decades centers on knowing what is normal. The complete lack of any cerebral pathologic abnormality is aberrant for a