Normal Pressure Hydrocephalus

Back

Practice Essentials

Normal pressure hydrocephalus (NPH) is a clinical symptom complex caused by the build-up of cerebrospinal fluid. This condition is characterized by abnormal gait, urinary incontinence, and (potentially reversible) dementia. See the image below.



View Image

T2-weighted MRI showing dilatation of ventricles out of proportion to sulcal atrophy in a patient with normal pressure hydrocephalus. The arrow points....

Signs and symptoms

Patients with NPH present with a gradually progressive disorder. The classic triad consists of the following:

See Clinical Presentation for more detail.

Diagnosis

Laboratory testing

In general, laboratory testing is not helpful in the diagnosis of NPH. However, a levodopa challenge may be helpful to rule out idiopathic Parkinson disease; patients with NPH have no significant response to levodopa or dopamine agonists.

Imaging studies

Imaging studies are invaluable in the diagnosis of NPH. In most cases of new-onset neurologic symptoms, obtain an initial computed tomography scan of the brain. Although magnetic resonance imaging is more specific than CT scanning in NPH, a normal CT scan can exclude the diagnosis.

Procedures

All patients with suspected NPH should undergo diagnostic CSF removal (either large volume lumbar puncture and/or external lumbar drainage), which has both diagnostic and prognostic value. Improvement in symptoms with large-volume drainage supports the diagnosis of NPH.

See Workup for more detail.

Management

Surgery

Surgical CSF shunting remains the main treatment modality for NPH. Prior to embarking upon surgical therapy, knowing which patients may benefit from surgery is necessary. Detailed testing is performed before and after CSF drainage (eg, baseline neuropsychological evaluation, timed walking test, large-volume lumbar puncture, external lumbar drainage, CSF infusion testing).

Ideal candidates for shunt surgery would show imaging evidence of ventriculomegaly, as indicated by a frontal horn ratio exceeding 0.50 on imaging studies, along with one or more of the following criteria:

An alternative technique to shunt surgery is endoscopic third ventriculostomy.

Pharmacotherapy

No definitive evidence exists that medication, including levodopa/carbidopa, can successfully treat NPH. Although levodopa/carbidopa has been reported to be of benefit in anecdotal reports, patients with NPH may represent misdiagnosed cases of parkinsonism. However, in patients who are poor candidates for shunt surgery, repeated lumbar punctures in combination with acetazolamide may be considered.[1]

See Treatment and Medication for more detail.

Background

Normal pressure hydrocephalus (NPH) is a clinical symptom complex characterized by abnormal gait, urinary incontinence, and dementia. It is an important clinical diagnosis because it is a potentially reversible cause of dementia. First described by Hakim in 1965, NPH describes hydrocephalus in the absence of papilledema and with normal cerebrospinal fluid (CSF) opening pressure on lumbar puncture.[2]

Pathophysiology

NPH differs from other causes of adult hydrocephalus. An increased subarachnoid space volume does not accompany increased ventricular volume. Clinical symptoms result from distortion of the central portion of the corona radiata by the distended ventricles. This may also lead to interstitial edema of the white matter and impaired blood flow, as suggested in nuclear imaging studies. The periventricular white matter anatomically includes the sacral motor fibers that innervate the legs and the bladder, thus explaining the abnormal gait and incontinence. Compression of the brainstem structures (ie, pedunculopontine nucleus) could also be responsible for gait dysfunction, particularly the freezing of gait that has been well described. Dementia results from distortion of the periventricular limbic system.

The term normal pressure hydrocephalus was based on the finding that all 3 patients reported by Hakim and Adams showed low CSF pressures at lumbar puncture, namely 150, 180, and 160 mm H2 O. However, an isolated CSF pressure measurement by lumbar puncture clearly yields a poor estimation of the real intracranial pressure (ICP) in patients with NPH.

Hakim first described the mechanism by which a normal or high-normal CSF pressure exerts its effects. Using the equation, Force = Pressure X Area, increased CSF pressure over an enlarged ependymal surface applies considerably more force against the brain than the same pressure in normal-sized ventricles. Normal pressure hydrocephalus may begin with a transient high-pressure hydrocephalus with subsequent ventricular enlargement. With further enlargement of the ventricles, CSF pressure returns to normal; thus the term NPH, at least in view of the initial pathophysiologic events, is a misnomer. Intermittent intracranial hypertension has been noted in some patients.

Some authors prefer the term extraventricular obstructive hydrocephalus. They believe that the initial event is diminished CSF absorption at the arachnoid villi. This obstruction to CSF flow leads to transient high-pressure hydrocephalus with subsequent ventricular enlargement. As the ventricles enlarge, CSF pressure returns to normal.

Frequency

International

See the list below:

Mortality/Morbidity

Race

Race is not associated with the development of NPH.

Sex

Gender is not associated with the development of NPH.

Age

NPH is predominantly a disease of the elderly, and thus with the aging of the population, its recognition is of increased importance. The Norwegian study mentioned above showed the incidence and prevalence of NPH increasing with age.[3]

History

Patients present with a gradually progressive disorder. As noted above, the classic triad consists of abnormal gait, urinary incontinence, and dementia. The gait disturbance is typically the earliest feature noted and considered to be the most responsive to treatment. The primary feature is thought to resemble an apraxia of gait. True weakness or ataxia is typically not observed.

The gait of NPH is characterized as bradykinetic, broad based, magnetic, and shuffling. The urinary symptoms of NPH can present as urinary frequency, urgency, or frank incontinence. While incontinence can result from gait disturbance and dementia, in a study by Sakakibara and colleagues, 95% of patients had urodynamic parameters consistent with detrusor overactivity.[7]

The dementia of NPH is characterized by prominent memory loss and bradyphrenia. Frontal and subcortical deficits are particularly pronounced. Such deficits include forgetfulness, decreased attention, inertia, and bradyphrenia. The presence of cortical signs such as aphasia or agnosia should raise suspicion for an alternate pathology such as Alzheimer disease or vascular dementia. However, comorbid pathology is not uncommon with advancing age. In one study, more than 60% of patients with iNPH had cerebrovascular disease.[8] In another similar study, more than 75% had Alzheimer disease pathology at the time of shunt surgery.[9]

Patients commonly present with a gait disorder and dementia. On neurologic examination, pyramidal tract findings may be present in addition to the above findings.

Causes

Normal pressure hydrocephalus may occur due to a variety of secondary causes but may be idiopathic in approximately 50% of patients. Secondary causes of NPH include head injury, subarachnoid hemorrhage, meningitis, and CNS tumor. Another potential cause could be previously compensated congenital hydrocephalus.[10]

Laboratory Studies

After a detailed history and physical examination, further diagnostic testing is required to establish a diagnosis. In general, laboratory testing is unhelpful. However, imaging tests are invaluable in the diagnosis of this disease.

Imaging Studies

In most cases of new onset neurologic symptoms, a CT scan of the brain is initially obtained. Although MRI is more specific than CT in NPH, a normal CT scan can exclude the diagnosis. CT and MRI findings in NPH include the following:

To establish a diagnosis of NPH (and exclude hydrocephalus ex vacuo), an MRI or CT must show an Evan’s index of at least 0.3.[12] In addition, one or more of the following must also be present:

Prominent medial temporal cortical atrophy favors a diagnosis of hydrocephalus ex vacuo and is related to Alzheimer disease or vascular dementia. Patients may occasionally be referred for treatment of NPH based on an imaging diagnosis of hydrocephalus. However, with hydrocephalus ex vacuo, transependymal flow is uncommon. In contrast, sulcal atrophy and significant white matter ischemic disease are commonly seen. See the images below.



View Image

This image shows ventriculomegaly, which is typical in hydrocephalus ex vacuo.



View Image

This image shows cortical atrophy, which is the defining feature of hydrocephalus ex vacuo.

Additionally, the presence of abnormalities such as an Arnold Chiari malformation raise the possibility of a congenital hydrocephalus.

Procedures

All patients with suspected NPH should undergo diagnostic CSF removal (either large volume lumbar puncture and/or external lumbar drainage [ELD]), which has both diagnostic and prognostic value (see Surgical Care). When the CSF opening pressure is greatly elevated, other causes of hydrocephalus should be considered, although CSF pressures may be transiently elevated in NPH. Improvement in symptoms with large volume drainage is supportive of the diagnosis of NPH.

ELD has a greater impact on brain volume expansion compared with lumbar puncture. In one study 20 patients with NPH based on clinical and radiological criteria were divided into 2 equal groups of 10 that underwent lumbar puncture or ELD. The median volume of CSF removed was 35 mL in patients who underwent lumbar puncture and 406 mL in patients who underwent ELD. Brain volume change was significantly larger in patients who underwent ELD than in patients who underwent lumbar puncture (p = 0.022) and correlated with the volume of CSF removal (r = 0.628, p = 0.004). Brain volume expansion was most pronounced adjacent to the lateral ventricles but was also detectable in the temporal and frontal regions. The median ventricular volume decreased after CSF removal. Ventricular volume reduction was more pronounced in patients who underwent ELD than in patients who underwent LP.[13]

Medical Care

A levodopa challenge may be helpful to rule out idiopathic Parkinson disease. Patients with normal pressure hydrocephalus (NPH) have no significant response to levodopa or dopamine agonists.

Surgical Care

Surgical CSF shunting remains the main treatment modality. Prior to embarking upon surgical therapy, knowing which patients may benefit from surgery is necessary. Detailed testing is performed before and after CSF drainage.

Initially, patients are given a baseline neuropsychological evaluation (eg, Folstein test or formal neuropsychological evaluation) and a timed walking test. Patients then undergo a lumbar puncture with removal of approximately 50 mL of CSF. Testing is then repeated 3 hours later. A clear-cut improvement in mental status and/or gait predicts a favorable response to shunt surgery. Improvement in gait may be seen in the form of reduced time to walk a fixed distance, reduced gait apraxia, or reduced freezing of gait. Videotaping the gait evaluation before and after the large volume lumbar puncture or lumbar drain placement can be helpful in decision making. Reduction in bladder hyperactivity also may be a sign of good outcome from shunting. Occasionally, improvement may be delayed and appear 1-2 days after the large-volume lumbar punctures. For a more objective assessment, videotape the timed walking test before and after lumbar puncture.

While large volume lumbar puncture was the earliest invasive diagnostic test in predicting response to shunt surgery, external lumbar drainage (ELD) is being used with increased frequency. In this method, clinicians use an indwelling CSF catheter in lieu of repeated lumbar punctures. The drainage catheter is generally left in place for 3 days, allowing sufficient time for return of neuronal function.[14] This method carries a higher risk of meningeal infection but may allow for a more accurate prognosis.[15]

In a prospective study of 151 patients with suspected idiopathic NPH, all patients underwent ELD. Patients with clinical improvement after ELD were offered shunt surgery, 90% of whom improved.[16] Others have confirmed the positive predictive value of improvement after ELD.[14, 17] Less clear, however, is the negative predictive value of ELD. In one study, 64% of patients who underwent shunt surgery had improvement, despite a negative ELD result.[18] Thus, given the dramatic improvement in quality of life for shunt responders, some have advocated for less reliance on predictive testing.[19, 20] Given the potential morbidity and mortality of shunt surgery, however, this has not been widely adopted.

An alternative method of predicting response to shunt surgery is CSF infusion testing. In this test, 2 lumbar drains are placed. One drain is used for continuous pressure monitoring while the other drain is used to continuously infuse solution into the CSF space. Elevated pressures during infusion are specific for shunt-responsive NPH. However, due to a lower sensitivity and potential morbidity, this is infrequently used.

Patients with a good response to predictive testing should be considered for ventriculoperitoneal or ventriculoatrial shunting. The best results are reported in patients who have no adverse risk factors; have responded favorably to a large-volume lumbar puncture; and have definite evidence of dementia and ataxia, CT scan or MRI evidence of chronic hydrocephalus, and a normal CSF at lumbar puncture. Some evidence indicates that patients with gait disturbance, mild or no incontinence, and mild dementia fare best among shunt surgery patients.[19, 21]

Another modality without significant current use is isotope cisternography. The method involves injecting a radiolabeled isotope into the CSF space. Using this method, the excretion of the isotope can be monitored. Lack of visualization of the isotope over the brain (ie, impaired absorption of the arachnoid villa) suggests a diagnosis of NPH. This test is rarely used due to the low positive predictive value with regards to shunt-responsiveness.

The clinical usefulness of cisternography was evaluated in a large-scale study (n=76) by Vanneste et al.[22] The predictive value of a scale based on combined clinical and CT scan criteria was established first, followed by an assessment of the predictive value of cisternography. Predictions based on cisternograms were identical to those of the clinical/CT scan scale in 43%, better in 24%, and worse in 33%. This suggests that cisternography does not improve the diagnostic accuracy of combined clinical and CT scan criteria in patients with presumed normal pressure hydrocephalus.

In summary, an ideal candidate for shunt surgery would show imaging evidence of ventriculomegaly indicated by a frontal horn ratio exceeding 0.50 on imaging studies along with one or more of the following criteria:

An alternative technique to shunt surgery is gaining some currency. This involves endoscopic third ventriculostomy (ETV). Although it has been previously used in noncommunicating hydrocephalus, its use has also been examined in patients with NPH.

One study examining this technique followed a series of 36 patients divided into a group of 29 patients with secondary communicating hydrocephalus and a group of 7 patients with normal pressure hydrocephalus. Sixteen (44.4%) of the patients had a previous ventriculoperitoneal shunt placement that presented with shunt malfunction. ETV was considered successful in 27 of 36 patients (75%). A Kaplan-Meier analysis revealed that the successful proportion of ETVs in secondary communicating hydrocephalus at 0.5, 1, and 3 months of follow-up was 0.83, 0.8, and 0.77, respectively; in the idiopathic NPH group, it was 0.83 initially and became stable at 0.66 after the first month. However, these results need to be replicated with larger series before the use of this technique is determined.[23]

Consultations

A neurologist should be initially involved in the evaluation of suspected NPH, at which time a lumbar puncture is performed. For appropriate patients, a neurosurgical consultation should also be obtained.

Medication Summary

No definitive evidence exists that medication can successfully treat NPH. While levodopa/carbidopa has been reported to be of benefit in anecdotal reports, these patients with NPH may represent misdiagnosed cases of parkinsonism. Currently, no definitive evidence exists that levodopa/carbidopa is an effective treatment for NPH. In patients who are poor candidates for shunt surgery, however, repeated lumbar punctures in combination with acetazolamide may be considered.[1]

Prognosis

The overall prognosis of NPH remains poor both due to a lack of improvement in some patients following surgery as well as a significant complication rate. In a study by Vanneste et al, one of the more comprehensive studies described above, marked improvement was noted in only 21% of patients following shunt surgery. Complication rate was approximately 28% with death or severe residual morbidity in 7% of patients, further emphasizing the importance of careful patient selection.[24] Concomitant cerebrovascular disease is a recognized negative prognostic factor.[25]

In a small prospective study, Hamilton et al measured the impact of cortical Alzheimer disease pathology on shunt responsiveness in 37 individuals treated for idiopathic NPH. Clinical measures, including neuropsychometrics and gait, were correlated with amyloid β (Aβ) plaques, neuritic plaques, and neurofibrillary tangles observed in cortical biopsies obtained during shunt insertion. Patients with no tau and Aβ pathology and mild tau and Aβ pathology improved on the neuropsychometric and gait evaluations. In contrast, patients with moderate-to-severe pathology did not show improvement on any study measure. However, the relatively small numbers in the study, presence of contradictory studies, and absence of a widely accepted biomarker for Alzheimer disease make it difficult to use this finding while evaluating patients with NPH.[26]

In patients who develop recurrent symptoms after initial improvement, shunt malfunction should be suspected and an evaluation for mechanical failure should be pursued. In some of these cases, catheter migration may have occurred, which is a correctable cause of shunt malfunction. In one case series, shunt revision was required in more than half of treated patients over a 6-year period, with improvement in most of these patients.[27]

The incidence of shunt complications is estimated in 30-40% of patients.[21] These include anesthetic complications, intracranial hemorrhage from placement of the ventricular catheter, infection, CSF hypotensive headaches, subdural hematomas, shunt occlusion, and catheter breakage. Rapid reduction in ventricular size following the shunt favors complications such as subdural hematoma, which may occur in 2-17% of patients.[21] Dual-switch valves and programmable valves may reduce the incidence of this complication.[28]

Patient Education

For excellent patient education resources, visit eMedicineHealth's Brain and Nervous System Center. Also, see eMedicineHealth's patient education article Normal Pressure Hydrocephalus.

What is normal pressure hydrocephalus (NPH)?What is the classic symptom triad for normal pressure hydrocephalus (NPH)?What is the role of lab testing in the evaluation of normal pressure hydrocephalus (NPH)?What is the role of imaging studies in the diagnosis of normal pressure hydrocephalus (NPH)?Which procedures are performed in the workup of normal pressure hydrocephalus (NPH)?What is the role of surgery in the treatment of normal pressure hydrocephalus (NPH)?What is the role of drug treatment for normal pressure hydrocephalus (NPH)?How is normal pressure hydrocephalus (NPH) characterized?What is the pathophysiology of normal pressure hydrocephalus (NPH)?What is the global prevalence of normal pressure hydrocephalus (NPH)?What are the racial predilections of normal pressure hydrocephalus (NPH)?How does the prevalence of normal pressure hydrocephalus (NPH) vary by sex?In which age groups is normal pressure hydrocephalus (NPH) most prevalent?Which clinical history findings suggest normal pressure hydrocephalus (NPH)?What causes normal pressure hydrocephalus (NPH)?How is Parkinson’s disease differentiated from normal pressure hydrocephalus (NPH)?What are the differential diagnoses for Normal Pressure Hydrocephalus?What is the role of lab studies in the workup of normal pressure hydrocephalus (NPH)?What is the role of imaging studies in the workup of normal pressure hydrocephalus (NPH)?How is a diagnosis of normal pressure hydrocephalus (NPH) established from imaging results?How is hydrocephalus ex vacuo differentiated from normal pressure hydrocephalus (NPH) on imaging?Which procedures are performed in the workup of normal pressure hydrocephalus (NPH)?What is the role of medications in the treatment of normal pressure hydrocephalus (NPH)?What is the role of surgery in the treatment of normal pressure hydrocephalus (NPH)?What is included in preoperative care for shunt surgery in the treatment of normal pressure hydrocephalus (NPH)?How is external lumbar drainage (ELD) used to predict response to shunt surgery for normal pressure hydrocephalus (NPH)?What is the role of isotope cisternography in surgical care for normal pressure hydrocephalus (NPH)?Who is the ideal candidate for shunt surgery for the treatment of normal pressure hydrocephalus (NPH)?What is an alternative treatment to shun surgery for normal pressure hydrocephalus (NPH)?Which specialist consultations are needed for the treatment of normal pressure hydrocephalus (NPH)?Which medications are beneficial in the treatment of normal pressure hydrocephalus (NPH)?What is the prognosis of normal pressure hydrocephalus (NPH)?What is the incidence of shunt complications following surgery for normal pressure hydrocephalus (NPH)?What is included in patient education for normal pressure hydrocephalus (NPH)?

Author

Michael J Schneck, MD, MBA, Vice Chair and Professor, Departments of Neurology and Neurosurgery, Loyola University, Chicago Stritch School of Medicine; Associate Director, Stroke Program, Director, Neurology Intensive Care Program, Medical Director, Neurosciences ICU, Loyola University Medical Center

Disclosure: Received honoraria from Boehringer-Ingelheim for speaking and teaching; Received honoraria from Sanofi/BMS for speaking and teaching; Received honoraria from Pfizer for speaking and teaching; Received honoraria from UCB Pharma for speaking and teaching; Received consulting fee from Talecris for other; Received grant/research funds from NMT Medical for independent contractor; Received grant/research funds from NIH for independent contractor; Received grant/research funds from Sanofi for independe.

Specialty Editors

Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Nestor Galvez-Jimenez, MD, MSc, MHA, The Pauline M Braathen Endowed Chair in Neurology, Chairman, Department of Neurology, Program Director, Movement Disorders, Department of Neurology, Division of Medicine, Cleveland Clinic Florida

Disclosure: Nothing to disclose.

Chief Editor

Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, Tampa General Hospital, University of South Florida Morsani College of Medicine

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Ceribell, Eisai, Greenwich, Growhealthy, LivaNova, Neuropace, SK biopharmaceuticals, Sunovion<br/>Serve(d) as a speaker or a member of a speakers bureau for: Eisai, Greenwich, LivaNova, Sunovion<br/>Received research grant from: Cavion, LivaNova, Greenwich, Sunovion, SK biopharmaceuticals, Takeda, UCB.

Additional Contributors

Arif I Dalvi, MD, Director, Movement Disorders Center, NorthShore University Health System; Clinical Associate Professor of Neurology, University of Chicago Pritzker Medical School

Disclosure: Nothing to disclose.

Ashvini P Premkumar, MD, Associate Director, Movement Disorders Center, NorthShore University HealthSystem, Clinical Instructor of Neurology, University of Chicago Pritzker Medical School

Disclosure: Nothing to disclose.

References

  1. Aimard G, Vighetto A, Gabet JY, Bret P, Henry E. [Acetazolamide: an alternative to shunting in normal pressure hydrocephalus? Preliminary results]. Rev Neurol (Paris). 1990. 146(6-7):437-9. [View Abstract]
  2. Hakim S, Adams RD. The special clinical problem of symptomatic hydrocephalus with normal cerebrospinal fluid pressure. Observations on cerebrospinal fluid hydrodynamics. J Neurol Sci. 1965 Jul-Aug. 2(4):307-27. [View Abstract]
  3. Brean A, Eide PK. Prevalence of probable idiopathic normal pressure hydrocephalus in a Norwegian population. Acta Neurol Scand. 2008 Jul. 118(1):48-53. [View Abstract]
  4. Hiraoka K, Meguro K, Mori E. Prevalence of idiopathic normal-pressure hydrocephalus in the elderly population of a Japanese rural community. Neurol Med Chir (Tokyo). 2008 May. 48(5):197-99; discussion 199-200. [View Abstract]
  5. Tanaka N, Yamaguchi S, Ishikawa H, Ishii H, Meguro K. Prevalence of possible idiopathic normal-pressure hydrocephalus in Japan: the Osaki-Tajiri project. Neuroepidemiology. 2009. 32(3):171-5. [View Abstract]
  6. Marmarou A, Young HF, Aygok GA. Estimated incidence of normal pressure hydrocephalus and shunt outcome in patients residing in assisted-living and extended-care facilities. Neurosurg Focus. 2007 Apr 15. 22(4):E1. [View Abstract]
  7. Sakakibara R, Uchiyama T, Kanda T, Uchida Y, Kishi M, Hattori T. [Urinary dysfunction in idiopathic normal pressure hydrocephalus]. Brain Nerve. 2008 Mar. 60(3):233-9. [View Abstract]
  8. Bech-Azeddine R, Hogh P, Juhler M, Gjerris F, Waldemar G. Idiopathic normal-pressure hydrocephalus: clinical comorbidity correlated with cerebral biopsy findings and outcome of cerebrospinal fluid shunting. J Neurol Neurosurg Psychiatry. 2007 Feb. 78(2):157-61. [View Abstract]
  9. Golomb J, Wisoff J, Miller DC, et al. Alzheimer's disease comorbidity in normal pressure hydrocephalus: prevalence and shunt response. J Neurol Neurosurg Psychiatry. 2000 Jun. 68(6):778-81. [View Abstract]
  10. Graff-Radford NR, Godersky JC. Symptomatic congenital hydrocephalus in the elderly simulating normal pressure hydrocephalus. Neurology. 1989 Dec. 39(12):1596-600. [View Abstract]
  11. Sasaki M, Honda S, Yuasa T, Iwamura A, Shibata E, Ohba H. Narrow CSF space at high convexity and high midline areas in idiopathic normal pressure hydrocephalus detected by axial and coronal MRI. Neuroradiology. 2008 Feb. 50(2):117-22. [View Abstract]
  12. Gyldensted C. Measurements of the normal ventricular system and hemispheric sulci of 100 adults with computed tomography. Neuroradiology. 1977 Dec 31. 14(4):183-92. [View Abstract]
  13. Singer OC, Melber J, Hattingen E, Jurcoane A, Keil F, Neumann-Haefelin T, et al. MR volumetric changes after diagnostic CSF removal in normal pressure hydrocephalus. J Neurol. 2012 May 17. [View Abstract]
  14. Williams MA, Razumovsky AY, Hanley DF. Comparison of Pcsf monitoring and controlled CSF drainage diagnose normal pressure hydrocephalus. Acta Neurochir Suppl. 1998. 71:328-30. [View Abstract]
  15. Governale LS, Fein N, Logsdon J, Black PM. Techniques and complications of external lumbar drainage for normal pressure hydrocephalus. Neurosurgery. 2008 Oct. 63(4 Suppl 2):379-84; discussion 384. [View Abstract]
  16. Marmarou A, Young HF, Aygok GA, et al. Diagnosis and management of idiopathic normal-pressure hydrocephalus: a prospective study in 151 patients. J Neurosurg. 2005 Jun. 102(6):987-97. [View Abstract]
  17. Murai R, Hashiguchi F, Kusuyama A, et al. Percutaneous stenting for malignant biliary stenosis. Surg Endosc. 1991. 5(3):140-2. [View Abstract]
  18. Walchenbach R, Geiger E, Thomeer RT, Vanneste JA. The value of temporary external lumbar CSF drainage in predicting the outcome of shunting on normal pressure hydrocephalus. J Neurol Neurosurg Psychiatry. 2002 Apr. 72(4):503-6. [View Abstract]
  19. Burnett MG, Sonnad SS, Stein SC. Screening tests for normal-pressure hydrocephalus: sensitivity, specificity, and cost. J Neurosurg. 2006 Dec. 105(6):823-9. [View Abstract]
  20. Stein SC, Burnett MG, Sonnad SS. Shunts in normal-pressure hydrocephalus: do we place too many or too few?. J Neurosurg. 2006 Dec. 105(6):815-22. [View Abstract]
  21. Hebb AO, Cusimano MD. Idiopathic normal pressure hydrocephalus: a systematic review of diagnosis and outcome. Neurosurgery. 2001 Nov. 49(5):1166-84; discussion 1184-6. [View Abstract]
  22. Vanneste J, Augustijn P, Davies GA, Dirven C, Tan WF. Normal-pressure hydrocephalus. Is cisternography still useful in selecting patients for a shunt?. Arch Neurol. 1992 Apr. 49(4):366-70. [View Abstract]
  23. Rangel-Castilla L, Barber S, Zhang YJ. The role of endoscopic third ventriculostomy in the treatment of communicating hydrocephalus. World Neurosurg. 2012 Mar. 77(3-4):555-60. [View Abstract]
  24. Vanneste J, Augustijn P, Dirven C, Tan WF, Goedhart ZD. Shunting normal-pressure hydrocephalus: do the benefits outweigh the risks? A multicenter study and literature review. Neurology. 1992 Jan. 42(1):54-9. [View Abstract]
  25. Boon AJ, Tans JT, Delwel EJ, et al. Dutch Normal-Pressure Hydrocephalus Study: the role of cerebrovascular disease. J Neurosurg. 1999 Feb. 90(2):221-6. [View Abstract]
  26. Hamilton R, Patel S, Lee EB, Jackson EM, Lopinto J, Arnold SE. Lack of shunt response in suspected idiopathic normal pressure hydrocephalus with Alzheimer disease pathology. Ann Neurol. 2010 Oct. 68(4):535-40. [View Abstract]
  27. Pujari S, Kharkar S, Metellus P, Shuck J, Williams MA, Rigamonti D. Normal pressure hydrocephalus: long-term outcome after shunt surgery. J Neurol Neurosurg Psychiatry. 2008 Nov. 79(11):1282-6. [View Abstract]
  28. Hertel F, Zuchner M, Decker C, Schill S, Bosniak I, Bettag M. The Miethke dual switch valve: experience in 169 adult patients with different kinds of hydrocephalus: an open field study. Minim Invasive Neurosurg. 2008 Jun. 51(3):147-53. [View Abstract]
  29. Brooks M. CSF Protein a Diagnostic Marker for Idiopathic NPH? Medscape Medical News. July 05, 2013. Available at http://www.medscape.com/viewarticle/807381. Accessed: July 16, 2013.
  30. Nishida N, Nagata N, Toda H, Ishikawa M, Urade Y, Iwasaki K. L-PGDS could be a surrogate marker of frontal lobe dysfunction in idiopathic NPH [abstract 1014]. Available at http://www.mdsabstracts.com/abstract.asp?MeetingID=798&id=107057. Accessed: July 16, 2013.
  31. Tisell M, Hellstrom P, Ahl-Borjesson G, Barrows G, Blomsterwall E, Tullberg M. Long-term outcome in 109 adult patients operated on for hydrocephalus. Br J Neurosurg. 2006 Aug. 20(4):214-21. [View Abstract]
  32. Tsakanikas D, Relkin N. Normal pressure hydrocephalus. Semin Neurol. 2007 Feb. 27(1):58-65. [View Abstract]
  33. Walter C, Hertel F, Naumann E, Morsdorf M. Alteration of cerebral perfusion in patients with idiopathic normal pressure hydrocephalus measured by 3D perfusion weighted magnetic resonance imaging. J Neurol. 2005 Dec. 252(12):1465-71. [View Abstract]
  34. Wikkelso C, Andersson H, Blomstrand C, Lindqvist G, Svendsen P. Normal pressure hydrocephalus. Predictive value of the cerebrospinal fluid tap-test. Acta Neurol Scand. 1986 Jun. 73(6):566-73. [View Abstract]

T2-weighted MRI showing dilatation of ventricles out of proportion to sulcal atrophy in a patient with normal pressure hydrocephalus. The arrow points to transependymal flow.

T2-weighted MRI showing dilatation of ventricles out of proportion to sulcal atrophy in a patient with normal pressure hydrocephalus. The arrow points to transependymal flow.

CT head scan of a patient with normal pressure hydrocephalus showing dilated ventricles. The arrow points to a rounded frontal horn.

This image shows ventriculomegaly, which is typical in hydrocephalus ex vacuo.

This image shows cortical atrophy, which is the defining feature of hydrocephalus ex vacuo.

T2-weighted MRI showing dilatation of ventricles out of proportion to sulcal atrophy in a patient with normal pressure hydrocephalus. The arrow points to transependymal flow.

CT head scan of a patient with normal pressure hydrocephalus showing dilated ventricles. The arrow points to a rounded frontal horn.

This image shows ventriculomegaly, which is typical in hydrocephalus ex vacuo.

This image shows cortical atrophy, which is the defining feature of hydrocephalus ex vacuo.