Description
Normal pressure hydrocephalus (NPH) is a clinical condition characterised by the triad of gait disturbance, dementia, and urinary incontinence, alongside radiological evidence of ventricular enlargement without significant elevation in cerebrospinal fluid (CSF) pressure.
Pathogenesis
The exact pathophysiology of NPH remains elusive, but it is widely accepted that the condition results from abnormal CSF dynamics. It is hypothesised that resistance to CSF outflow leads to the gradual enlargement of cerebral ventricles, causing distortion and dysfunction of surrounding brain tissues. Additionally, impaired absorption of CSF may cause the ventricles to enlarge, compressing the brain’s tissue and leading to the clinical symptoms of NPH.
Subtype
- Idiopathic NPH: This is the most common subtype, with the cause being unknown.
- Secondary NPH: This occurs as a result of known factors that affect CSF dynamics, such as meningitis, subarachnoid haemorrhage, or traumatic brain injury.
Epidemiology, Risk Factors & Associations
- Prevalence increases with age, especially significant in those over 60 years (up to 5% of this population may be affected).
- Men are affected more commonly than women.
- Risk factors include a history of hypertension, heart disease, diabetes, Parkinson’s disease, and stroke.
Clinical Features
“Wet, Wacky, Wobbly” – Clinical triad present in <60% at initial presentation which includes:
- Urinary incontinence
- Cognitive impairment (manifesting as forgetfulness, lack of interest, and a slow response)
- Gait disturbance (typically an early feature characterised by a broad-based, magnetic, shuffling walk)
Complications
- Potential complications include a decline in mental function, decreased mobility, and decreased overall quality of life.
- There is also a risk of complications from treatment, such as infection or bleeding from shunt placement.
Radiological Features
General Features
- Characteristically demonstrates ventriculomegaly out of proportion to cortical atrophy, particularly affecting the lateral ventricles, and the third ventricle. The fourth ventricle is usually normal.
- Widening of the temporal horns of the lateral ventricles >6 mm, not accounted for by hippocampal atrophy.
- Disproportionately Enlarged Subarachnoid space Hydrocephalus (DESH):
- Disproportionate enlargement of the subarachnoid spaces, especially widening of the Sylvian fissures and insular cisterns, but;
- Effacement of the sulci and subarachnoid spaces at the vertex and medial/parafalcine region.
- Cingulate sulcus sign – posterior half of the cingulate sulcus is narrower than the anterior half
- Acute callosal angle (less than 90 degrees), indicative of frontal horn rounding.
- Upward bowing of the corpus callosum.
CT
- Non-contrast: Shows ventriculomegaly, particularly of the lateral and third ventricles. Cortical sulci at the vertex may be effaced due to dilation of the ventricles.
- Contrast-enhanced: No specific features related to NPH.
MRI
- T1WI: Ventriculomegaly with relative preservation of cortical and subcortical brain volume.
- T2WI: Ventriculomegaly. High signal in the periventricular white matter due to transependymal CSF flow.
- T1 C+: No specific features related to NPH.
- DWI/ADC: No specific features related to NPH.
Grading and Staging
There is no universally accepted grading or staging system for NPH.
Diagnosis
Diagnosis requires clinical evaluation, imaging, and often CSF pressure monitoring or assessment of response to high-volume lumbar puncture or CSF diversion.
Clinical response to CSF tap is the gold standard for establishing diagnosis.
Differential Diagnosis
- Alzheimer’s disease: More severe cortical atrophy and memory impairment, typically normal ventricle size.
- Parkinson’s disease: Characteristic extrapyramidal signs with substantia nigra signal changes on MRI.
- Multi-infarct dementia: Multiple lacunar infarcts on imaging, history of stroke, stepwise decline in cognitive function.
- Communicating hydrocephalus: Often associated with a history of meningitis or subarachnoid haemorrhage. Increased ventricle size proportional to the cortical atrophy.
Management
Management typically involves CSF shunting, with ventriculoperitoneal shunt placement being the most common procedure. Neurosurgical consultation is required.