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.
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
Brain tumor or head trauma
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.
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).
Notable difficulty turning on the body’s long axis (multistep turns)
Gait initiation failure or freezing of gait
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
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
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.
Endoscopic third ventriculostomy (ETV):
Indicated in locally confined, infratentorial, extraventricular obstruction to CSF flow