HYDROCEPHALUS AND SHUNTS: WHAT THE NEUROLOGIST SHOULD KNOW
- Correspondence to: Mr Ian K Pople, Department of Neurosurgery, Frenchay Hospital, Frenchay Park Road, Bristol BS16 1LE, UK: ikpople{at}hotmail.com
The second most common reason for being sued for negligence in neurosurgery is a problem related to hydrocephalus management (the first being spinal surgery!). However, the good news is that the overall standard of care for patients with hydrocephalus appears to have greatly improved over the last 10 years with the advent of better facilities for investigation, new approaches to treatment, and a greater awareness of the need for adequate follow up. In the possible absence of a local neurosurgeon with an interest in hydrocephalus, a neurologist who is faced with the ongoing care of a patient with hydrocephalus should ideally have a clear idea of what exactly constitutes appropriate follow up and which clinical and radiological warning signals of shunt problems to look out for.
DEFINITIONS
Hydrocephalus is an excessive accumulation of cerebrospinal fluid (CSF) within the head caused by a disturbance of formation, flow or absorption.
“Hydrocephalus ex vaccuo” is a misnomer. It refers to asymptomatic ventricular enlargement caused by generalised loss of cerebral tissue, from severe head injury, infarction or cerebral hypoxia.
“Normal pressure hydrocephalus” is also a misnomer. It describes a condition in older adults of low grade hydrocephalus with intermittently raised intracranial pressure (ICP) (usually at night) causing the classic Adam’s triad of symptoms—gait apraxia, incontinence, dementia.
BASIC HYDROCEPHALUS PATHOPHYSIOLOGY IN ADULTS
The normal CSF production rate in an adult is 0.35 ml/min (20 ml/hour or 500 ml/24 hours). The capacity of normal lateral and third ventricles is approximately 20 ml, whereas the total CSF volume in an adult is 120–150 ml. Hence, in normal circumstances CSF is recycled over three times each day.
ICP rises if production of CSF exceeds absorption, but CSF production will fall as ICP rises to high levels, and compensation (stabilisation of hydrocephalus at a new steady state) may occur through transventricular absorption of CSF. Dural …
