Normal pressure hydrocephalus
Normal pressure hydrocephalus (NPH) remains a controversial entity with often ambiguous imaging findings.
The majority of cases of normal pressure hydrocephalus (NPH) are idiopathic and is referred to as primary NPH. Many causes of secondary NPH exist including 3:
The classical clinical findings of normal pressure hydrocephalus are 1-3:
- urinary incontinence
- deterioration in cognition
- gait disturbances
These can be remembered with the unkind mnemonic Wet, Wacky and Wobbly.
As the name suggests mean CSF opening pressure in patients with NPH is within the normal range (<18 cm H2O or 13 mm Hg) 3.
A classic neurological sign in NPH is magnetic gait.
The underlying cause of NPH remains controversial. One theory is that NPH is an obstructive type of communicating hydrocephalus due to reduced of CSF resorption. A second theory suggests that NPH results from weakening of the ventricular wall due to periventricular white matter ischemic damage 3.
Although CT is able to visualise the anatomical changes of NPH, it is inferior to MRI.
- ventriculomegaly 1-3
- crowding of the gyri at the vertex (with small sulci)
- sylvian fissures out of proportion to sulcal enlargement (which is minimal) and hippocampus and mesial temporal lobe volumes (which are near normal)
- aqueductal flow void
- best seen on T2 spin echo sequences14
- favorable outcome if shunt surgery has been suggested but other work suggests that it is an unreliable marker of actual flow 12.
- periventricular high signal on T2 weighted sequences
- MR spectroscopy - lactate peak in lateral ventricles
- CSF flow studies 3
- increased aqueductal stroke volume
- increased aqueductal peak velocity
- various publications have set various normal and abnormal ranges
- flow rate of >24.5mL/min 95% specific for NPH 9,11
- stroke volume of 42 microL predicts good response from shunting 10
Nuclear medicine is less important in diagnosing NPH .Some of the features described are
- early detection of radiotracer in to lateral ventricles giving heart shaped appearance of lateral ventricles than a normal trident pattern13
- persistence of radiopharmaceutical beyond 24-48 hours due to impaired absorption13
- radiotracer doesnot extend to superior aspect of convexities of lateral ventricles13
- retrograde CSF flow in to lateral ventricles .13
Treatment and prognosis
Treatment of normal pressure hydrocephalus, once the diagnosis is established, is with CSF shunting, usually a ventriculoperitoneal shunt (VP shunt). The challenge is identifying those patients which will benefit from shunting. Favourable prognostic factors include 3:
- short duration of presurgical symptoms (less than 6 months)
- onset of gait disturbance before dementia
- temporary symptom relief from a CSF tap test (removal of 40ml of CSF via lumbar puncture)
- absence of significant cerebral vascular disease
- presence of an aqueductal flow void on T2 imaging10, 14
It is thought ot have been initially described by the neuroradiologists Salamon Hakim and R D Adams in 1965, although it may actually have been described under a different name earlier by McHugh 4,6-7.
Imaging imaging differential consideration include
- 1. Kitagaki H, Mori E, Ishii K et-al. CSF spaces in idiopathic normal pressure hydrocephalus: morphology and volumetry. AJNR Am J Neuroradiol. 1998;19 (7): 1277-84. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 2. Holodny AI, Waxman R, George AE et-al. MR differential diagnosis of normal-pressure hydrocephalus and Alzheimer disease: significance of perihippocampal fissures. AJNR Am J Neuroradiol. 1998;19 (5): 813-9. AJNR Am J Neuroradiol (abstract) - Pubmed citation
- 3. Hurley RA, Bradley WG, Latifi HT et-al. Normal pressure hydrocephalus: significance of MRI in a potentially treatable dementia. J Neuropsychiatry Clin Neurosci. 1999;11 (3): 297-300. J Neuropsychiatry Clin Neurosci (full text) - Pubmed citation
- 4. Bradley WG. Normal pressure hydrocephalus: new concepts on etiology and diagnosis. AJNR Am J Neuroradiol. 2000;21 (9): 1586-90. AJNR Am J Neuroradiol (full text) - Pubmed citation
- 5. Bradley WG, Scalzo D, Queralt J et-al. Normal-pressure hydrocephalus: evaluation with cerebrospinal fluid flow measurements at MR imaging. Radiology. 1996;198 (2): 523-9. Radiology (abstract) - Pubmed citation
- 6. Conn HO, Lobo FM. What do physicians know about normal pressure hydrocephalus and when did they know it? A survey of 284 physicians. Yale J Biol Med. 2008;81 (1): 19-29. Free text at pubmed - Pubmed citation
- 7. Hakim S, Adams RD. The special clinical problem of symptomatic hydrocephalus with normal cerebrospinal fluid pressure. Observations on cerebrospinal fluid hydrodynamics. J. Neurol. Sci. 1968;2 (4): 307-27. Pubmed citation
- 8. Ivkovic M, Liu B, Ahmed F et-al. Differential diagnosis of normal pressure hydrocephalus by MRI mean diffusivity histogram analysis. AJNR Am J Neuroradiol. 2013;34 (6): 1168-74. AJNR Am J Neuroradiol (full text) - doi:10.3174/ajnr.A3368 - Pubmed citation
- 9. Al-Zain FT, Rademacher G, Lemcke J et-al. [Idiopathic normal-pressure hydrocephalus. Flow measurement of cerebrospinal fluid using phase contrast MRI and its diagnostics importance]. Nervenarzt. 2007;78 (2): 181-7. doi:10.1007/s00115-006-2231-7 - Pubmed citation
- 10. Bradley WG, Scalzo D, Queralt J et-al. Normal-pressure hydrocephalus: evaluation with cerebrospinal fluid flow measurements at MR imaging. Radiology. 1996;198 (2): 523-9. Radiology (abstract) - Pubmed citation
- 11. Manley GT, Hemphill C, Stiver S. Intracranial Pressure and Brain Monitoring XIII. Springer. (2009) ISBN:3211855785. Read it at Google Books - Find it at Amazon
- 12. Krauss JK, Regel JP, Vach W et-al. Flow void of cerebrospinal fluid in idiopathic normal pressure hydrocephalus of the elderly: can it predict outcome after shunting?. Neurosurgery. 1997;40 (1): 67-73. Pubmed citation
- 13. Sandler MP, Coleman RE, Patton JA et-al. Diagnostic Nuclear Medicine. Lippincott Williams & Wilkins. (2003) ISBN:0781732522. Read it at Google Books - Find it at Amazon
- 14. Hayhow B, Begic F, Evans A et-al. Communicating hydrocephalus with reversible cognitive impairment. Aust N Z J Psychiatry. . doi:10.1177/0004867413511547 - Pubmed citation
Synonyms & Alternative Spellings
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