Hydrocephalus is usually defined as ventriculomegaly with sulcal effacement and can be classified as communicating, non- communicating or Normal Pressure Hydrocephalus.
Communicating Hydrocephalus is implied if the level of the obstruction is distal to the 4th ventricle while non communicating hydrocephalus is implied if the level of obstruction is cranial to the 4th ventricular outflow.
Normal Pressure hydrocephalus is a special sub-class of hydrocephalus with disproportionate ventricular dilatation relative to sulcal prominence.
All causes of hydrocephalus are typically treated by shunt procedures,
with external shunt procedures like Ventriculo-peritoneal (other shunts include ventriculo-pleural,
ventriculo-atrial and lumbo-peritoneal shunts) and internal drainage procedures like endoscopic third ventriculostomy (ETV).
External shunt procedures are usually considered the first line of surgical management,
while ETV is specifically used in obstructive hydrocephalus,
multiple external shunt failures and may also be used in Normal pressure hydrocephalus.
Normal pressure hydrocephalus is a subtype of chronic acquired hydrocephalus due to hyperdynamic circulation with a typical clinical triad of gait abnormalities (shuffling,
wide-based or "magnetic" gait),
dementia and urinary incontinence. Subtypes of Normal pressure hydrocephalus include primary or iNPH (idiopathic NPH) and secondary NPH (usually due to sclerosis of the arachnoid granulations),
the latter has best response to shunting.
The diagnosis of iNPH is complicated by an initial incomplete clinical triad of symptoms (Gait disturbances > Dementia> Urinary disturbance ),
and near normal CSF stroke volume,
going on to elevated CSF pressures (at which stage shunt surgery is most beneficial) and finally after a plateau,
a reduction in CSF stroke volume (when shunt surgery is not
Basic techniques for evaluation are the 2D anatomic images,
(T1W,
T2W and FLAIR images in multiple planes) or 3D T2W anatomic images (CISS,
FIESTA or DRIVE according to the vendor).
MRI of CSF flow dynamics directly involves qualitative and quantitative evaluation,
most commonly using time-resolved 2D phase contrast MRI with velocity encoding.
In the pre-operative setting,
it helps in answering the questions of why and where the obstruction to flow occurs,
as CSF Flow studies are more sensitive than conventional 2D or 3D images in visualization very low flows.
It can also be used to evaluate post-operative cases to either prove the satisfactory functioning of internal or external shunts,
or for serial follow up in progressive cases (with inoperable tumors).