Hydrocephalus

Hydrocephalus refers to the abnormal enlargement of cerebral ventricles and/or subarachnoid space as a result of excess cerebrospinal fluid (CSF) accumulation. There are four types, which include communicating hydrocephalus, non-communicating hydrocephalus, normal pressure hydrocephalus (NPH), and hydrocephalus ex vacuo. Communicating hydrocephalus typically occurs as a result of decreased CSF absorption or increased CSF production, whereas non-communicating hydrocephalus is due to the obstructed passage of CSF from the ventricles to the subarachnoidal space. Both forms lead to an elevated intracranial pressure (ICP), which leads to headache, nausea, and/or vomiting. These symptoms are often accompanied by specific clinical manifestations, such as macrocephaly in congenital hydrocephalus, or changes in vital signs resulting from brainstem compression. In contrast, normal pressure hydrocephalus, which is usually due to decreased CSF absorption in the elderly, manifests with normal ICP because of effective compensation by ventricular dilation. This ventricular distension leads to the classic presentation of urinary incontinence, dementia, and abnormal gait. In hydrocephalus ex vacuo, CSF extension occurs secondary to loss of brain tissue (e.g., cerebral atrophy); this type of hydrocephalus is actually a misnomer as it is not a true hydrocephalus. CT or MRI (and ultrasound for infants) are important diagnostic procedures. Treatment involves surgical insertion of a shunt, which drains excess CSF into another area of the body – usually the peritoneum.

Type of hydrocephalus	Etiology	Pathophysiology	Symptoms/Clinical findings	Diagnosis
Non-communicating hydrocephalus	Congenital Arnold-Chiari malformation Dandy-Walker malformation Intrauterine infections (see congenital infections) Acquired Brain tumor (especially medulloblastomas, ependymomas, and astrocytomas) Subarachnoidal or intraventricular hemorrhage → inflammatory response → fibrosis Inflammation (e.g., following recovery from bacterial meningitis)	Obstructed passage of CSF from the ventricles to the subarachnoidal space Obstruction of the aqueduct (connection between the third and fourth ventricle) Obstruction of the lateral foramen of Luschka Obstruction of the median foramen of Magendie (connection between the fourth ventricle to the external subarachnoid space)	Typical findings of raised ICP Headache, nausea, and vomiting Papilledema 6th nerve palsy Abnormal gait Impaired consciousness Cushing's triad (irregular breathing, widening pulse pressure, bradycardia) Additional findings in infants Macrocephaly: an enlarged head with a circumference > the average for a given age and sex by 2 standard deviations (as indicated by a percentile growth chart) Tense fontanelle Sunset sign Lower extremity spasticity, hyperreflexia Changes in vital signs resulting from brainstem compression	Ultrasonography Indication: clinical suspicion during antenatal period or in infants < 6 months of age (through the anterior fontanelle when it is still open) Findings: enlarged lateral ventricles MRI (preferred for children) or CT Indication: older infants (when fontanelle is already closed, typically > 6 months of age) or adults Features of acute hydrocephalus: enlarged ventricles Temporal horn dilation > 2 mm Evans ratio > 30% Sulcal enlargement Mickey Mouse ventricles Upward bowing of the corpus callosum
Communicating hydrocephalus	Inflammatory diseases of the central nervous system (CNS) → inflamed arachnoid villi Subarachnoidal or intraventricular hemorrhage → inflammatory response → fibrosis	↓ CSF absorption
	Choroid plexus papilloma or carcinoma Inflammation of the choroid plexus	↑ CSF production
Normal pressure hydrocephalus	Idiopathic (most common in adults > 60 years) Possible secondary causes: Inflammatory diseases of the CNS (e.g., meningitis) Intraventricular hemorrhage Subarachnoidal hemorrhage	↓ CSF absorption Secondary: impaired CSF absorption caused by inflammation and subsequent fibrosis of the subarachnoid villi	Classic Triad Wet: urinary incontinence Initially, only ↑ urgency and frequency of micturition → urge incontinence → later in the disease, incontinence worsens due to indifference of the patient to their recurrent urinary symptoms Additionally, the gait disturbances can make the way to the toilet more difficult, leading to further incontinence related issues Wacky: dementia Wobbly: frequent falls, broad-based gait with short steps (ataxic gait)	Rule out other causes of symptoms: Cognitive assessment Vitamin B12 level and thyroid function tests MRI (initial test), CT Ventriculomegaly without sulcal enlargement Periventricular hypodensity due to periventricular edema CSF tap test: confirmatory test Note severity of symptoms before the test Opening pressure is normal or slightly elevated Remove a small amount of CSF fluid (30–50 mL) Improvement of symptoms after CSF removal confirms NPH Lumbar puncture is both diagnostic and therapeutic
Hydrocephalus ex vacuo	Occurs in primary cerebral atrophy or cerebral destructive lesions Actually a misnomer; not a true hydrocephalus	Loss of brain tissue→ CSF extends to the inner and external subarachnoid space	Symptoms of the underlying condition	Resembles hydrocephalus on imaging Cortical atrophy may be prominent

Because the fontanelles of infants are still open, the accumulation of CSF can lead to macrocephaly, which may offset elevations in ICP and delay neurological symptoms!References:^{[1][2][3][4][5][6]}

Most types of hydrocephalus are progressive and present a risk of neurological damage. Definitive treatment of hydrocephalus involves the drainage of excess CSF via a cerebral shunt, usually into the peritoneum (e.g., ventriculoperitoneal or VP shunt).

• Cerebral shunt
  • Indications: hydrocephalus, syringomyelia
  • Important components
    • Inflow catheter
    • Adjustable one-way pressure valves
    • Outflow catheter
    • Reservoir
  • Complications
    • Underdrainage → ↑ ICP
    • Overdrainage
      • Symptoms: see intracranial hypotension syndrome
      • Variant: Slit ventricle syndrome
        • Pathophysiology: Ventricular walls are pulled into the catheter slit by suction and permanently close the slit.
    • Shunt infection (∼ 5% of cases)
      • Bacterial contamination (e.g., Staphylococcus epidermidis), often associated with biofilm formation
      • Therapy: shunt explantation surgery
• Possible interim therapy: diuretics, fibrinolysis, serial lumbar punctures, (acetazolamide)
• Alternative surgical procedures
  • Endoscopic third ventriculostomy
  • Choroid plexectomy (or coagulation)
  • Cerebral aqueductoplasty

References:^[1][7]