Clinical Pearls & Morning Reports
Published April 7, 2021
Ventriculomegaly may be identified with normal aging, Alzheimer’s disease, or chronic cerebrovascular disease, but an acute callosal angle (the angle at which the two lateral ventricles meet at the level of the posterior commissure) is highly suggestive of normal pressure hydrocephalus. Read the NEJM Case Records of the Massachusetts General Hospital here.
Q: Describe the classic clinical features of normal pressure hydrocephalus.
A: The classic triad of gait instability, cognitive impairment, and urinary incontinence distinguishes normal pressure hydrocephalus from other disorders. Unlike Parkinson’s disease, normal pressure hydrocephalus is not expected to cause a resting tremor. Postural instability and falls occur more frequently in patients with normal pressure hydrocephalus than in patients with Parkinson disease, especially early in the disease course.
Q: What cognitive deficits are characteristic of normal pressure hydrocephalus?
A: Cognitive features of normal pressure hydrocephalus include generalized slowing, which is usually more prominent than deficits in attention, concentration, or memory. Executive-function deficits and apathy are also common. Apathy that manifests as a lack of motivation is commonly identified as a psychiatric difficulty in patients with normal pressure hydrocephalus. The development of apathy can cause normal pressure hydrocephalus to mimic a depressive illness and thus can delay the diagnosis.
A: The standard diagnostic test is a motor and cognitive evaluation of the patient after cerebrospinal fluid (CSF) drainage by means of large-volume lumbar puncture or placement of an external lumbar drain. Improvement after drainage of a large volume (30 to 50 ml) of CSF by lumbar puncture has a high positive predictive value for improvement after ventriculoperitoneal shunting; however, false negative responses to lumbar puncture are fairly common. In patients with an unclear response or a lack of response to lumbar puncture, a trial of an external lumbar drain can be informative.
A: Ventriculoperitoneal shunting is performed to move CSF from one of the lateral ventricles into the peritoneal cavity, where it is absorbed by the peritoneal lining. When the abdomen is not accessible (e.g., when there is scarring related to a previous surgery or infection), another space, such as the pleural cavity or the bloodstream, may be used. Two types of valves can be used to control the amount of fluid that is drained: pressure-regulated and flow-regulated valves. Pressure-regulated valves open by means of a ball-valve mechanism whenever the intracranial pressure rises above a set level. These valves are often coupled with antisiphon devices, which prevent CSF overdrainage after sudden elevation of the head. Flow-regulated valves maintain a constant level of CSF flow, independent of head position and changes in intracranial pressure. The current standard of care is placement of a programmable valve, which allows the provider to adjust the resistance transcutaneously with magnets. The use of programmable valves, rather than fixed-setting valves, has significantly reduced the rate of shunt revision.