Low pressure hydrocephalus: issues of diagnosis and treatment in five cases

Five patients with hydrocephalus who failed to respond to apparently adequa te CSF drainage via a functioning shunt (four cases) or external ventricula r drain (one case) are described. In three of the four shunted cases, the s hunt was ventriculoperitoneal with a medium pressure valve, and in one a co mbination of peritoneal and atrial shunts both with low pressure valves. Al l five patients were tested for possible low pressure hydrocephalus by a pe riod of external ventricular drainage at heights of 0 to - 5 cm H2O below t he reference point (external auditory meatus - EAM). Four of the five patie nts showed rapid and significant clinical improvement and went on to shunt revision (three) or insertion (one). The shunts were then all peritoneal, o f which three were valveless, whilst one had a Sophy programmable valve at the lowest setting. In all four patients the improvement was sustained and was associated with a radiological (CT or MRI) improvement which varied fro m marked to slight. In the fifth patient there was no improvement with low pressure external drainage and no shunt revision was undertaken. On the bas is of these cases the possible entity of low pressure hydrocephalus is disc ussed with particular reference to mechanism, recognition and management.