Normal Pressure Hydrocephalus
Hydrocephalus is a general term, which denotes enlargement of the cerebral ventricles due to cerebrospinal fluid (CSF) accumulation. 1 Hydrocephalus may be congenital or acquired (e.g., through infection, head trauma, tumors, cysts, et cetera). There are several types of hydrocephalus, this article will focus on Normal Pressure Hydrocephalus.
Other Types:1. Hydrocephalus Ex Vacuo refers to ventricle expansion as a secondary result of brain tissue shrinkage or atrophy, as commonly seen in degenerative diseases such as Alzheimer’s disease (AD).2 2. Obstructive/ Non-Communicating Hydrocephalus results from the obstruction (due to tumor, bleeding, or developmental abnormalities) of the flow of CSF in the cerebral aqueduct (which leads to expansion of the first three ventricles; most common in children), at the outlets of the fourth ventricle (which produces expansion of the entire ventricular system), or at the interventricular foramina (which leads to expansion of the lateral ventricles) (see Figure 1). 2
Normal Pressure Hydrocephalus (a.k.a. “Hakim’s Syndrome) does not have a universally accepted definition in the literature. In NPH, CSF pressure has been described as normal or only slightly elevated, however, continuous measure of CSF flow may demonstrate an elevation of CSF pressure at times. Price and colleagues 3 define NPH as “ a clinical syndrome whose manifestations result from subarachnoid space obstruction or impedance, of whatever cause, to normal CSF flow from the basal cisterns, over the cerebral convexities, to the superior sagittal sinus, where it is returned to the systematic circulation.” Some sources define NPH as a form of communicating hydrocephalus becoming symptomatic later in life and often of unknown etiology (“idiopathic”).4 Some researchers/clinicians also acknowledge a non-communicating NPH, where obstruction of CSF flow results from scarring remains of old trauma or infection, from hemorrhage or tumor.53. Non-Obstructive/Communicating Hydrocephalus results from the disturbance in the circulation of CSF through the subarachnoid space or in the reabsorption of the CSF at the arachnoid villi. As its name implies, there is free communication between the ventricles and subarachnoid space. 2
- Etiology NPH is attributable to subarachnoid hemorrhage, head trauma, a brain tumor (3rd and 4th ventricle and posterior fossa tumors are prevalent), congenital abnormalities such as aqueductal stenosis, intracranial surgery, meningitis, or idiopathic origin (although often correlated to subarachnoid fibrosis post-mortem). It is estimated that 50% of NPH is idiopathic, whereas 50% is secondary to subarachnoid hemorrhage, meningitis, cranial trauma, or intracranial surgery. NPH due to CSF reabsorption defects is a refuted theory because the ventricular enlargements seen in CSF would not be likely to a CSF reabsorption defect, where no pressure gradient between the ventricles and convexities is expected. 5
- Symptomatology The description of NPH syndrome appears to have altered over the years. First described by Hakim and Adams 6, NPH’s classical signs included memory impairment, a paucity and slowness of thought and action, unsteady gait, and urinary and fecal incontinence. Huckman 7 reported a wide range of symptoms, which presented in a continuum, such as impairment of consciousness (from mild inattentiveness to a comatose state), paucity of thought (from apathy to akinetic mutism), and gait disturbance (from mild motoric disorder to complete inability to walk or stand). Hartwig 8 reviews a series of literature, which lists numerous other symptoms associated with NPH: Parkinsonism features, “subcortical type” dementia (i.e., forgetfulness, inertia, inattention, decreased speed of complex information processing, and impaired ability to manipulate acquired knowledge), impairment of memory with recent onset, marked memory deficit for recent events, quantitative reduction in all speech, cognitive and motor activity with marked apathy, lack of spontaneity without other features of cortical dysfunction (e.g., absence of aphasia or agnosia), fear of falling where individuals tend to hang on, but can usually be displaced backwards more than forwards, and sudden and inexplicable falls. Psychiatric symptoms may also be present such as depression, irrational hostility and aggression, visual hallucinations, and mania. 3, 9
- Diagnosis As seen above, the clinical features of NPH are diverse, making accurate diagnosis of NPH difficult. Therefore, physiologic(radioisotope imaging, cisternography, cerebrospinal fluid infusion manometry) and morphologic (pneumocephalography and cranial computed axial tomography) diagnostic techniques are often emphasized. 5, 8 Nonetheless, some studies have taken a neuropsychological approach to diagnosing NPH. For instance, Botez and colleagues reported that in the early stages of NPH, lowered scores in the Wechsler Intelligence Scales (WAIS) were found in arithmetic, digit span, and timed tests, reflecting slowing and impaired attention and mental tracking. Left untreated, all scores become proportionately depressed. The use of the mini mental state exam (MMSE) is thought to be inadequate given that it excludes all patients with NPH with mild mental impairments (i.e., the best surgery candidates). Tasks that can detect frontal lobe dysfunction (e.g. trail making and Stroop) will reveal declines. Overall, neuropsychological tests may not differentiate NPH from other subcortical dementias but may render cortical dementia (e.g., AD) improbable. EEG is not diagnostic but may show delta and theta waves in 50% of patients. 3
- Prevalence NPH is an infrequent cause of dementia, with an estimated incidence of 1.3 to 2.2 per million per year. However, it is estimated to be present in up to 92% of elderly patients with otherwise unexplained gait disturbances. 10
- Treatment The treatment of NPH is ventriculoperitoneal or ventriculoatrial shunting, where a shunt is inserted into a ventricle and connected to a subcutaneous tube that drains CSF into the peritoneal cavity or the right atrium of the heart, respectively. Probatory removal of 30-50 ml of CSF by spinal tap may be used to select shunting candidates, given that improvement of gait disturbance after probatory removal is predictive of gait and general amelioration after shunting.9 Clinical improvement after CSF removal or shunting may be attributed to several factors, including increased periventricular blood flow along with improvement of metabolism subsequent to reduction of intracranial pressure, decrease of CSF pulse pressure, and normalization of compliance. In contrast, the parallel existence of morphologic white matter damage may limit recovery of clinical symptoms. 10
- Complications Shunts may become blocked or infected and the patient may develop subdural effusion or seizures. Subdural hematomas (usually bilateral) is seen in as many as 21% of shunt patients.3 The total number of postsurgical complications is estimated to be 30-40%, resulting in death or severe residual morbidity in 5-15%. 5
- Effectiveness Improvements of patients with the clinical triad of NPH (dementia, gait disturbance, and urinary incontinence) range from 40-50%, with gait disturbance being the symptom to most likely improve. Gait disturbance is an important symptom to note because it is a predominant clinical symptom of idiopathic NPH, which (on some accounts) responds best to shunting (i.e., patients who walk well before shunting usually do not improve). Improvement may be observed within the first 48 hours and may continue for months. If no improvement is noted, further deterioration may be prevented. 3, 9 Other sources estimate substantial improvement in 30% of idiopathic NPH and 50-70% improvement where etiology was known.5
- Woodard, J.L. (1998). Dementia. Encyclopedia of Mental Health, 1, p.711.
- Kolb, B., Whishaw, I.Q. (1996). Fundamentals of Human Neuropsychology, 4th edition. W.H. Freeman and Company: New York.
- Price, T. R. Tucker, G. J. (1977). Psychiatric and Behavioral manifestations of Normal Pressure Hydrocephalus. The Journal of Nervous and Mental Diseases, 164 (1), 51-55.
- Ogden, J. A. (1986). Neuropsychological and psychological sequalae of shunt surgery in young adults with hydrocepahlus. Journal of Clinical and Experimental Neuropsychology, 8 (6), 657-679.
- Vanneste, J.A.L. (1994). Three decades of normal pressure hydrocephalus: Are we wiser now? Journal of Neurology, Neurosurgery, and Psychiatry, 57, 1021-1025.
- Hakim, S., Adams, R.D. (1965). The special clinical problem of symptomatic hydrocephalus with normal cerebrospinal fluid dynamics. Journal of Neurological Sciences, 2, 307-327.
- Huckman, M.S. (1981). Normal Pressure Hydrocephalus: Evaluation of diagnostic and prognostic tests. American Journal of Neuroradiology, 2 (5), 385-395.
- Hariwig, W. (1983). Neuropsychological Assessment of Normal Pressure Hydrocephalus. Clinical Neuropsychology, 5 (2), 88-92.
- Masters, J.C. & O’Grady, M. (1992). Normal pressure hydrocephalus: A potentially reversible form of dementia. Journal of Psychosocial Nursing, 30 (6), 25-27.
- Krauss, J.K, Faist, M., Schubert, M., Burreman, J.J., Lucky, C.A., and Berger, W. (2001). Evaluation of Gait in normal pressure hydrocephalus before and after shunting. Gatit Disorder Advances in Neurology, 87, 301-309.