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Normal pressure hydrocephalus (NPH)

Potentially reversible syndrome characterized by enlarged cerebral ventricles (ventriculomegaly), cognitive impairment, gait apraxia and urinary incontinence. in the absence of another cause.

Normal pressure hydrocephalus (NPH) is a gradual accumulation of cerebrospinal fluid (CSF) that causes the ventricles of the brain to enlarge. The condition occurs with a normal or slightly elevated CSF pressure. | Jorge Muniz/Medcomic

Introduction

Potentially reversible syndrome characterized by enlarged cerebral ventricles (ventriculomegaly), cognitive impairment, gait apraxia and urinary incontinence. in the absence of another cause.

  • M/C form of hydrocephalus in adults.

History:

In 1761, Giambattista Morgagni described 3 autopsy cases of “chronic senile hydrocephalus” in subjects older than 60 years of age. However, the clinical syndrome of normal-pressure hydrocephalus (NPH) was only recognized in 1965 by Colombian neurosurgeon Salomón Hakim and American neurologist, Raymond D. Adams.

Aetiology

Idiopathic NPH (iNPH) (50% cases):

NPH with no identifiable cause, primarily observed in adults older than 60 years.

Secondary NPH (sNPH):

Can occur at any age
  • Subarachnoid hemorrhage
  • Meningitis
  • Intracerebral hemorrhage
  • Brain tumor or head trauma

Pathophysiology

This schematic drawing illustrates various models of the pathophysiology of idiopathic normal pressure hydrocephalus (iNPH). Any model must explain how and why the ventricles enlarge, how neuronal and glial dysfunction occurs to produce the clinical features, and why symptoms improve with shunt surgery (ie, reversible neuronal and glial dysfunction). Proposed disturbances in the CSF dynamic system that contribute to ventricular enlargement and dysfunction of the brain parenchyma include impaired CSF outflow resistance and increased intracranial pressure pulsatility. The gait and cognitive disturbances of iNPH are thought to be of periventricular/subcortical/frontal origin. The arterial supply of this area is mainly via periventricular end arteries, sensitive to a subcritical ischemia that causes dysfunction, but not infarction in an anatomic distribution, that affects the axons related to symptoms (eg, those to the leg, as represented in the homunculus). The altered CSF dynamics and reduced subcortical blood flow and metabolism may give rise to periventricular hyperintensities seen on MRI in iNPH. | CSF = cerebrospinal fluid; ICP = intracranial pressure. | Williams, M. A., & Malm, J. (2016). Diagnosis and Treatment of Idiopathic Normal Pressure Hydrocephalus. Continuum (Minneapolis, Minn.), 22(2 Dementia), 579–599. https://doi.org/10.1212/CON.0000000000000305

Clinical faetures

Hakim-Adams triad:

Cassically described by Colombian neurosurgeon Salomon Hakim and R D Adams in 1965. Generally, gait disturbance plus one additional feature is required to consider the diagnosis.
  • Gait disturbance: Impairments of gait and balance are typically the first symptoms to be noticed and may be very mild at the outset.
  • Urinary incontinence: Result from detrusor hyperactivity owing to the partial/total absence of central inhibitory control
  • Dementia: Ventricular enlargement pushes the cortex against the inner table of the calvarium, radial shearing forces lead to dementia.

Gait disturbances:

The occurrence of gait abnormality before the onset of cognitive decline has been reported to predict a better prognosis after shunting. The most common description of iNPH gait is “shuffling,” “magnetic,” and “wide-based.” With disease progression, the patient’s gait deteriorates finally becoming broad-based, slow, short-stepped, and glue-footed (a gait disturbance of the astasia-abasia type).
  • External rotation in foot posture
  • Poor foot clearance (festination, shuffling, tripping)
  • Notable difficulty turning on the body’s long axis (multistep turns) 
  • Gait initiation failure or freezing of gait

Diagnosis

Diagnostic flowchart. If NPH is suspected on clinical and radiological grounds, diagnostic accuracy can be secured with invasive testing (CSF drainage or measurement of CSF dynamic variables such as compliance and resistance to outflow). Such tests are often needed for adequate confirmation of the indication for shunting, particularly in patients with iNPH. | *1In the 10 m gait test, at least 20% improvement; in psychometric tests, at least 10% improvement. | PVI, pressure-volume index; Rout, resistance to outflow | Kiefer, M., & Unterberg, A. (2012). The differential diagnosis and treatment of normal-pressure hydrocephalus. Deutsches Arzteblatt international, 109(1-2), 15–26. https://doi.org/10.3238/arztebl.2012.0015

Brain imaging:

Other than ventriculomegaly, there is no definitive pathological or radiological diagnostic finding for NPH, which is frequently over-suspected and under-confirmed, based only on positive response to CSF shunting.
  • Evans index: Frontal horn ratio defined as the maximal frontal horn ventricular width divided by the transverse inner diameter of the skull; it signifies ventricular enlargement if it is greater than or equal to 0.3.
  • Callosal angle: 40-90° in iNPH
  • Disproportionate widening of the ventricles in comparison to the cerebral sulci may be present.
  • Narrow high-convexity sulci: Coronal section at level of posterior commissure shows narrowed subarachnoid space surrounding the outer brain surface (a “tight convexity”) and narrow medial cisterns.
  • Dilated Sylvian fissures
  • Disproportionately enlarged subarachnoid space hydrocephalus (DESH): Focally dilated sulci
  • Peri-ventricular hypodensities in CT/T2/fluid-attenuated inversion recovery hyperintensities: Represents transependymal edema due to elevated CSF pressure, but may also be seen in small vessel ischemic disease
  • Bulging of lateral ventricular roof: Upward bowing and stretching of the corpus callosum
  • CSF flow study: Flow rate > 24.5 mL/min
Neuroimaging in NPH (A) Axial FLAIR MRI scan showing a significant ventriculomegaly with increased Evans Index, the ratio of maximum width of the frontal horns of the lateral ventricles and maximal internal diameter of skull at the same level on axial CT or MRI images. In this case, Evans index is 0.39 (abnormal > 0.3) (B) T1-weighted coronal gadolinium-enhanced MRI scan showing reduced callosal angle. (C) Axial FLAIR MRI scan revealing enlarged lateral ventricles with bright signal in the surrounding white matter, suggestive of transependymal edema. (D) Axial FLAIR MRI showing narrowing of the sulci and subarachnoid spaces over the high convexity and midline surface in the frontoparietal regions. | Oliveira, L. M., Nitrini, R., & Román, G. C. (2019). Normal-pressure hydrocephalus: A critical review. Dementia & neuropsychologia, 13(2), 133–143. https://doi.org/10.1590/1980-57642018dn13-020001

Large-volume lumbar puncture (LVLP) or tap test:

Temporarily decreasing intraventricular pressure, mimicking the effect of a shunting procedure, allowing the physician to evaluate the patient’s response to a substantial (50 ml) CSF removal
An example of ASL-MRI illustrating a positive correlation between enhanced CBF and clinical improvement after large-volume spinal tap (unpublished data). | Oliveira, L. M., Nitrini, R., & Román, G. C. (2019). Normal-pressure hydrocephalus: A critical review. Dementia & neuropsychologia, 13(2), 133–143. https://doi.org/10.1590/1980-57642018dn13-020001

Differential diagnosis:

Differential Diagnosis of Idiopathic Normal Pressure Hydrocephalus | Williams, M. A., & Malm, J. (2016). Diagnosis and Treatment of Idiopathic Normal Pressure Hydrocephalus. Continuum (Minneapolis, Minn.), 22(2 Dementia), 579–599. https://doi.org/10.1212/CON.0000000000000305

Management

Ventriculoperitoneal (VP) shunt:

Standard treatment of NPH. A shunt is inserted with a proximal and distal catheter, into ventricular or lumbar subarachnoid space and the peritoneal cavity, respectively. In between, there is a valve that opens in response to the changes in pressure between the catheters. That change is pressure varies from the supine to upright position and hence an important factor in determining the effectiveness of a shunt.
This lateral skull film shows both a conventional differential-pressure valve (black arrow) and a gravity-controlled valve (white arrow). One can also see an ICP telemetry probe that has been implanted into the brain (blue arrow) for long-term ICP measurement, enabling optimal setting of the opening pressure of the adjustable G valve. | Photograph: Neuroradiology Dept., Universitätsklinikum des Saarlandes

Endoscopic third ventriculostomy (ETV):

Indicated in locally confined, infratentorial, extraventricular obstruction to CSF flow

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