The special clinical problem of symptomatic hydrocephalus with normal cerebrospinal fluid pressure: Observations on cerebrospinal fluid hydrodynamics

Abstract

In a series of personally observed cases, three of which are reported in detail, the authors have noted that a state of symptomatic hydrocephalus may exist in the presence of normal CSF pressure. The patients had exhibited mental dullness, inattentiveness, psychomotor retardation, unsteadiness of gait, and incontinence of urine, a syndrome which may be mistakenly ascribed to a degenerative or traumatic vascular disease of the cerebrum. Ventriculo-atrial shunt corrected this condition and permitted recovery by lowering the CSF pressure 20 or more mm of water. An important factor, heretofore overlooked, in explaining this symptomatic hydrocephalus with relatively normal CSF pressure is that the force exerted on the ventricular wall represents a product of pressure times surface area. A given pressure exerts a greater force in a large ventricular system than in a small one. A pressure of 170 or 180 mm H 2O in ventricles that are three times normal size may produce symptoms, whereas it would not do so in a normal-sized ventricular system. This hydraulic press hypothesis must be applied in all cases of hydrocephalus. Without some knowledge of ventricular size in this condition, the CSF pressure cannot be accurately evaluated. This physical principle applies not only to adult hydrocephalus but also to infantile hydrocephalus, where the cranium expands, and to certain types of porencephaly and postoperative meningeal cysts and possibly syringomyelia.