Hydrocephalus & CSF Cysts

Hydrocephalus is excessive accumulation of cerebrospinal fluid (CSF) within the ventricular system, producing ventricular dilation. It is one of the most common neurosurgical conditions and a major cause of childhood neurologic morbidity. CSF cysts (arachnoid cysts, colloid cysts, others) are separate conditions that share with hydrocephalus the property of CSF-related space-occupying or flow-disturbing pathology. This page covers hydrocephalus, CSF flow physiology, and CSF cysts.

CSF Physiology

Production

  • Total CSF volume ~150 mL.
  • Daily production ~500 mL (turnover 3-4 times per day).
  • ~70% from choroid plexus (located in lateral, third, and fourth ventricles).
  • ~30% from interstitial fluid (transependymal).

Circulation

  1. Lateral ventricles → foramina of Monro → third ventricle → aqueduct of Sylvius → fourth ventricle → foramina of Luschka (lateral) and Magendie (median) → subarachnoid space (basal cisterns and over hemispheres).
  2. Absorbed at arachnoid granulations into superior sagittal sinus.
  3. Recent recognition of meningeal lymphatic drainage and glymphatic clearance as additional pathways.

Classification of Hydrocephalus

Communicating Hydrocephalus

CSF can flow through the ventricular system but cannot be absorbed normally. Causes:

  • Post-meningitic scarring of subarachnoid space (especially TB, fungal).
  • Post-hemorrhagic (especially after SAH).
  • Idiopathic / age-related (normal-pressure hydrocephalus, NPH).
  • Carcinomatous meningitis.
  • Excess CSF production (choroid plexus papilloma/carcinoma).
  • Pseudotumor cerebri (idiopathic intracranial hypertension) — actually elevated CSF pressure without ventriculomegaly.

Non-Communicating (Obstructive) Hydrocephalus

Block in the ventricular system:

  • Aqueductal stenosis: congenital (X-linked or autosomal recessive) or acquired (post-inflammatory, post-hemorrhagic, neoplastic).
  • Foramen of Monro obstruction: colloid cyst, tumor (SEGA in TSC).
  • Fourth ventricle obstruction: medulloblastoma, ependymoma, cerebellar mass effect.
  • Chiari I, II malformation: can produce hydrocephalus via cerebellar tonsillar obstruction of 4th ventricle outlets.

Clinical Features of Hydrocephalus

Acute / Subacute Hydrocephalus

  • Headache (often worse in morning, with Valsalva).
  • Nausea and vomiting.
  • Visual disturbances (papilledema, sometimes diplopia from CN VI palsy).
  • Altered consciousness.
  • Gait abnormalities.

Chronic Hydrocephalus

  • Insidious cognitive decline.
  • Gait disorder.
  • Urinary incontinence.
  • Headache may be mild or absent.

Infantile Hydrocephalus

  • Increasing head circumference (open sutures allow expansion).
  • Bulging fontanelle.
  • “Sunset” eyes (upgaze paresis from compressed midbrain).
  • Irritability, poor feeding.
  • Developmental delay if untreated.

Pathology of Hydrocephalus

  • Ventricular dilation, often disproportionate to cortical atrophy.
  • Periventricular interstitial edema (transependymal CSF flow).
  • Compression of corpus callosum (stretched and thinned).
  • Effacement of cortical sulci.
  • Chronic: cortical atrophy.
  • Severe chronic: white matter damage from periventricular pressure.

Normal Pressure Hydrocephalus (NPH)

Classical Triad (Hakim Triad)

  • Gait apraxia (“magnetic gait”): wide-based, slow, shuffling.
  • Cognitive decline: subcortical pattern.
  • Urinary incontinence: urgency, then frank incontinence.

Pathology

  • Ventricular enlargement disproportionate to cortical atrophy.
  • “Hydrocephalus ex vacuo” pattern excluded.
  • Sometimes signs of chronic transependymal flow.
  • Often with coexisting cerebrovascular pathology.

Diagnosis

  • Clinical triad.
  • MRI: ventriculomegaly with disproportionate enlargement (Evans index > 0.30).
  • Tap test: lumbar puncture removing 30-50 mL CSF; improvement supports diagnosis.
  • Extended lumbar drainage trial.

Treatment

  • Ventriculoperitoneal shunt: dramatic improvement in selected patients (~60-70% benefit).
  • Programmable valves used.

Hydrocephalus Ex Vacuo

Apparent ventricular enlargement due to underlying cerebral atrophy (Alzheimer disease, vascular dementia, chronic alcoholism). The CSF expands to fill space left by atrophic brain. Pressure is normal. Not true hydrocephalus. Distinguish from NPH by atrophy disproportionate to ventricles (vs ventricles disproportionate to atrophy in NPH).

Idiopathic Intracranial Hypertension (Pseudotumor Cerebri)

  • Elevated ICP without mass lesion or ventricular dilation.
  • Predominantly young, obese women.
  • Headache, papilledema, visual obscurations, CN VI palsy.
  • CSF opening pressure elevated.
  • Associated with transverse sinus stenosis in many patients.
  • Treatment: weight loss, acetazolamide, sometimes optic nerve sheath fenestration or shunting; transverse sinus stenting in selected.

Treatment of Hydrocephalus

  • Ventricular shunt (VP, VA, etc.): most common; CSF drained to peritoneum, atrium, or pleura.
  • Endoscopic third ventriculostomy (ETV): creates opening in floor of third ventricle; effective for obstructive hydrocephalus from aqueductal stenosis.
  • External ventricular drain (EVD): temporary; for acute hydrocephalus.
  • Manage underlying cause (tumor resection, infection treatment).

CSF Cysts

Arachnoid Cyst

  • CSF-filled cyst lined by arachnoid membrane.
  • Most common locations: middle cranial fossa (Sylvian fissure), retrocerebellar, suprasellar.
  • Usually congenital; can also be post-traumatic.
  • Often incidental; most don’t grow or cause symptoms.
  • Symptoms: headache, seizures, focal deficits if mass effect.
  • Treatment: observation; fenestration if symptomatic.

Colloid Cyst

  • Cyst at the foramen of Monro.
  • Can cause acute obstructive hydrocephalus → sudden death if large.
  • Histology: cyst lined by ciliated epithelium with mucinous content.
  • Often present with positional headache.
  • Treatment: surgical resection.

Rathke Cleft Cyst

  • Pituitary region; remnant of Rathke pouch.
  • Often incidental.
  • Can cause endocrine or visual symptoms.

Epidermoid Cyst

  • Squamous epithelium-lined cyst with cheesy keratin content.
  • Most common locations: cerebellopontine angle, supratentorial.
  • Cauliflower-like appearance.
  • Restricted diffusion on MRI (key feature distinguishing from other cysts).

Dermoid Cyst

  • Contains hair, sebaceous glands, sometimes teeth.
  • Midline locations preferred.
  • Rare; sometimes associated with dermal sinus tract.

Neurenteric Cyst

Rare; spinal or intracranial; endodermal lining.

Chiari Malformations

Chiari I

  • Cerebellar tonsils descend below foramen magnum.
  • Symptoms: cough-induced headache, neck pain, sometimes syringomyelia → cape distribution sensory loss + UMN signs.
  • Surgical decompression for symptomatic.

Chiari II

  • Severe; with myelomeningocele.
  • Cerebellum + brainstem + 4th ventricle displaced caudally.
  • Hydrocephalus common.
  • Requires myelomeningocele closure and ventricular shunt.

Chiari III

Occipital encephalocele; severe and rare.

🔍 Did You Know?

The “endoscopic third ventriculostomy (ETV)” has become a major alternative to shunting for obstructive hydrocephalus, particularly aqueductal stenosis. In this procedure, the neurosurgeon endoscopically perforates the floor of the third ventricle (the tuber cinereum, just behind the mammillary bodies), creating a new pathway for CSF to flow directly into the prepontine cistern. The advantages over shunting are substantial: no foreign hardware, no shunt malfunction, no shunt infection, no need for revisions, and lower long-term complication rates. Success rates depend heavily on patient selection — ETV works best for older children and adults with obstructive hydrocephalus from aqueductal stenosis or distal obstruction (e.g., tectal lesion). Infants and patients with communicating hydrocephalus tend to do less well. The ETV Success Score (ETVSS) helps stratify risk based on age, etiology, and prior shunt history. The procedure illustrates a broader trend in modern neurosurgery: less is sometimes more, and avoiding indwelling hardware can transform long-term outcomes. The same principle has driven minimally invasive approaches across neurosurgery and neuroradiology. The lesson: when treating hydrocephalus, careful evaluation of the obstruction and the likely benefit of ETV can spare many patients a lifetime of shunt-related morbidity.

Pitfalls and Pearls

  • Communicating hydrocephalus: CSF flows through ventricles but absorption impaired (post-meningitic, post-SAH, NPH).
  • Obstructive hydrocephalus: ventricular blockage (aqueductal stenosis, mass).
  • NPH triad: magnetic gait + cognitive decline + urinary incontinence; shunt-responsive in selected.
  • Hydrocephalus ex vacuo: atrophy-driven ventricular enlargement; not true hydrocephalus; pressure normal.
  • Aqueductal stenosis: congenital or acquired; ETV effective.
  • Colloid cyst: foramen of Monro; sudden death risk.
  • Arachnoid cyst: middle cranial fossa most common; usually incidental.
  • Epidermoid cyst: cauliflower-like; restricted diffusion (distinguishes from other cysts).
  • Chiari I + syringomyelia: cape distribution sensory loss + headache.
  • Chiari II + myelomeningocele: hydrocephalus common.
  • Idiopathic intracranial hypertension (IIH): papilledema + headache + young obese women + transverse sinus stenosis.
  • Endoscopic third ventriculostomy: alternative to shunting for obstructive hydrocephalus.
  • Sunset eyes: infantile hydrocephalus; CN III + upgaze paresis.
  • Transependymal flow on MRI: periventricular hyperintensity; acute hydrocephalus.

References

  1. Love S, Budka H, Ironside JW, Perry A, eds. Greenfield’s Neuropathology. 9th ed. CRC Press; 2015.
  2. Bret P, Guyotat J, Chazal J. Is normal pressure hydrocephalus a valid concept in 2002? A reappraisal in five questions and proposal for a new designation of the syndrome as “chronic hydrocephalus.” J Neurol Neurosurg Psychiatry. 2002;73(1):9-12.
  3. Kulkarni AV, Drake JM, Mallucci CL, et al. Endoscopic third ventriculostomy in the treatment of childhood hydrocephalus. J Pediatr. 2009;155(2):254-259.e1.
  4. Friedman DI, Liu GT, Digre KB. Revised diagnostic criteria for the pseudotumor cerebri syndrome. Neurology. 2013;81(13):1159-1165.
  5. Hakim S, Adams RD. The special clinical problem of symptomatic hydrocephalus with normal cerebrospinal fluid pressure. J Neurol Sci. 1965;2(4):307-327.