Neurology · Hydrocephalus
The facts most likely to be tested
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Normal pressure hydrocephalus presents with the classic Hakim triad of gait disturbance, urinary incontinence, and dementia.
Communicating hydrocephalus results from impaired cerebrospinal fluid (CSF) reabsorption at the arachnoid granulations, often secondary to meningitis or subarachnoid hemorrhage.
Non-communicating (obstructive) hydrocephalus is caused by a physical blockage of CSF flow within the ventricular system, most commonly at the aqueduct of Sylvius.
Infants with hydrocephalus present with macrocephaly, bulging fontanelle, and the 'sunsetting' sign due to increased intracranial pressure.
Large-volume lumbar puncture (tap test) is the key test for predicting shunt response in normal pressure hydrocephalus, performed to demonstrate clinical improvement following CSF removal.
Ventriculoperitoneal (VP) shunt placement is the standard treatment for communicating hydrocephalus, while endoscopic third ventriculostomy (ETV) is preferred for obstructive hydrocephalus due to aqueductal stenosis.
Papilledema can be seen in older children and adults with chronic elevated intracranial pressure due to hydrocephalus, but it is often absent in infants (open sutures and fontanelle) and is not a feature of normal pressure hydrocephalus.
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Etiology / Epidemiology
Caused by impaired CSF absorption or obstruction of flow. Common in pediatrics (congenital) and elderly (NPH).
Clinical Manifestations
Triad of wet, wobbly, and wacky in NPH; sunset eyes and bulging fontanelle in infants.
Diagnosis
MRI brain is the preferred imaging; Evans index >0.3 indicates ventriculomegaly.
Treatment
Ventriculoperitoneal (VP) shunt is the usual definitive treatment; avoid lumbar puncture if signs of herniation exist.
Prognosis
Early VP shunt placement can limit permanent cognitive decline and motor deficits.
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Epidemiology & Etiology
Congenital cases often result from aqueductal stenosis or Chiari malformations. Acquired forms stem from meningitis, subarachnoid hemorrhage, or intraventricular tumors. NPH is a distinct form of communicating hydrocephalus seen in the elderly.
Pertinent Anatomy
CSF is produced in the choroid plexus and circulates through the ventricles. Obstruction at the foramen of Monro or cerebral aqueduct leads to non-communicating hydrocephalus. Reabsorption occurs at the arachnoid granulations.
Pathophysiology
Increased intracranial pressure (ICP) results from an imbalance between CSF production and resorption. In communicating hydrocephalus, CSF flows freely out of the ventricles, but its passage through the subarachnoid space or absorption at the arachnoid granulations is impaired. In non-communicating, a physical obstruction prevents flow between ventricles. Chronic pressure leads to ventricular dilation and compression of the surrounding cerebral parenchyma.
Clinical Manifestations
Infants present with macrocephaly, sunset eyes, and a tense, bulging fontanelle. Adults with NPH exhibit the classic triad: gait disturbance, urinary incontinence, and dementia. Cushing's triad (hypertension, bradycardia, irregular respirations) indicates life-threatening elevated ICP.
Diagnosis
MRI brain is the diagnostic study of choice to visualize ventricular size. The Evans index (ratio of the maximal width of the frontal horns to the maximal inner skull diameter on the same axial slice) >0.3 defines ventriculomegaly and supports, but does not by itself establish, the diagnosis. In NPH, a large-volume lumbar puncture showing clinical improvement is a key diagnostic predictor for shunt success.
Treatment
Surgical ventriculoperitoneal (VP) shunt is the definitive treatment for most forms; endoscopic third ventriculostomy (ETV) is an alternative for obstructive hydrocephalus (e.g., aqueductal stenosis). Lumbar puncture is contraindicated with obstructive hydrocephalus or a mass lesion with mass effect due to risk of cerebral herniation; papilledema warrants neuroimaging before LP. Acetazolamide may be used temporarily to decrease CSF production in select cases.
Prognosis
Untreated hydrocephalus leads to permanent brain damage and death. VP shunt complications include shunt infection and mechanical obstruction, requiring lifelong monitoring for recurrence of symptoms.
Differential Diagnosis
Normal Pressure Hydrocephalus: gait disturbance is usually the first symptom
Pseudotumor Cerebri: normal ventricular size on imaging
Subdural Hematoma: history of trauma with crescent-shaped lesion
Brain Tumor: focal neurological deficits present
Alzheimer's Dementia: lack of gait disturbance and urinary incontinence early on