Hydrocephalus & CSF Diversion
Bottom Line
Hydrocephalus is classified as obstructive (non-communicating) or communicating — the distinction drives treatment: obstructive → ETV candidate; communicating → VP shunt. NPH presents with the Hakim triad (wet, wacky, wobbly) — gait is first and most shunt-responsive. Shunt complications: obstruction is most common (proximal > distal); infection is usually Staph epidermidis within 6 months — requires hardware removal. IIH surgery: ONSF for vision, CSF shunting for headache, venous sinus stenting for documented stenosis with gradient >8 mmHg. Always try acetazolamide + weight loss first (IIHTT trial).
Types of Hydrocephalus
CSF Physiology
- CSF production: ~500 mL/day (0.35 mL/min); total volume ~150 mL; turns over 3–4× per day
- Primary source: choroid plexus (70%) in lateral, third, and fourth ventricles; remainder from ependymal lining and brain interstitial fluid
- Flow pathway: lateral ventricles → foramen of Monro → 3rd ventricle → aqueduct of Sylvius → 4th ventricle → foramina of Luschka (lateral) and Magendie (midline) → subarachnoid space → arachnoid granulations → dural venous sinuses
- Absorption: primarily via arachnoid granulations (villi) into the superior sagittal sinus; driven by pressure gradient between CSF and venous sinus
Classification
| Type | Mechanism | Common Causes | Treatment |
|---|
| Obstructive (non-communicating) | Blockage within ventricular system — CSF cannot exit ventricles | Aqueductal stenosis, posterior fossa tumor, colloid cyst (foramen of Monro), tectal glioma, pineal region tumor | ETV preferred; VP shunt if ETV fails |
| Communicating | Impaired absorption at arachnoid granulations; ventricles communicate freely with subarachnoid space | Post-SAH, post-meningitis, post-IVH, carcinomatous meningitis, choroid plexus papilloma (overproduction — rare) | VP shunt |
| Normal pressure (NPH) | Communicating; ICP intermittently elevated (B-waves) but normal on single measurement | Idiopathic (iNPH); secondary to SAH, meningitis, TBI | VP shunt with programmable valve |
| Ex vacuo | Ventricular enlargement from brain parenchymal loss — NOT true hydrocephalus | Alzheimer disease, stroke, diffuse atrophy | No treatment (no elevated pressure) |
Causes of Obstructive Hydrocephalus
- Aqueductal stenosis: most common cause of congenital obstructive hydrocephalus; congenital (X-linked L1CAM mutation) or acquired (post-infection, tectal glioma); lateral and 3rd ventricles dilated, 4th ventricle normal
- Posterior fossa tumors: medulloblastoma, pilocytic astrocytoma, ependymoma — compress 4th ventricle or aqueduct
- Pineal region tumors: germinoma, pineoblastoma — compress aqueduct from dorsal aspect; Parinaud syndrome (upgaze palsy, convergence-retraction nystagmus)
- Colloid cyst at foramen of Monro: ball-valve obstruction → acute bilateral lateral ventricle dilation; can cause sudden death — classic board scenario
Causes of Communicating Hydrocephalus
- Post-SAH: blood products impair CSF absorption at arachnoid granulations; acute (~20–30%) and chronic (~10–20%)
- Post-meningitis: inflammatory debris and fibrosis of arachnoid granulations
- Choroid plexus papilloma: CSF overproduction — rare cause; tumor produces CSF at >normal rate
- Carcinomatous meningitis: tumor cells clog arachnoid villi
Special Types
- Hydrocephalus ex vacuo: NOT true hydrocephalus; brain atrophy with proportionate ventriculomegaly and sulcal enlargement; no periventricular edema; no elevated ICP; do NOT shunt
- External hydrocephalus (benign enlargement of subarachnoid spaces): infants with macrocephaly; enlarged subarachnoid spaces over frontal convexities; normal or mildly enlarged ventricles; self-resolves by age 2; distinguished from subdural collections by cortical veins traversing the fluid space
Board Pearls
- Obstructive vs. communicating — determines treatment: obstructive → ETV; communicating → VP shunt
- Ex vacuo ventriculomegaly is NOT hydrocephalus — sulcal enlargement proportionate to ventricular enlargement; no periventricular transependymal edema; do NOT shunt
- Colloid cyst at foramen of Monro: can cause acute obstructive hydrocephalus and sudden death — classic board scenario
- Choroid plexus papilloma — the only cause of hydrocephalus from CSF overproduction
- External hydrocephalus in infants is benign and self-resolving — do NOT shunt
VP Shunt
Components & Mechanism
- Three components: proximal catheter (in lateral ventricle), valve mechanism, distal catheter (in peritoneal cavity)
- Proximal catheter placement: right lateral ventricle preferred (non-dominant hemisphere); inserted via burr hole at Kocher’s point (1 cm anterior to coronal suture, 2–3 cm lateral to midline)
- Trajectory: aim toward medial canthus of ipsilateral eye (coronal plane) and tragus (sagittal plane); typical depth 5–7 cm from cortical surface
- Distal catheter: tunneled subcutaneously from scalp → neck → chest → abdomen; tip in peritoneal cavity for CSF reabsorption
Valve Types
| Valve Type | Mechanism | Advantages | Disadvantages |
|---|
| Fixed-pressure | Opens at set pressure (low/medium/high) | Simple, reliable, no MRI interaction | Cannot adjust post-op; over- or under-drainage requires surgical revision |
| Programmable | Pressure setting adjusted externally with magnet | Non-invasive adjustment; fine-tune for optimal drainage; preferred for NPH | Older models may reset during MRI — must verify and reprogram after scanning |
| Anti-siphon device | Prevents excessive drainage when upright (gravity effect) | Reduces over-drainage and subdural collections | May cause under-drainage if malfunctioning |
Indications
- Communicating hydrocephalus (primary indication)
- Failed ETV
- NPH (with programmable valve)
- Infantile hydrocephalus (post-hemorrhagic, post-infectious)
- Post-SAH chronic hydrocephalus
VP vs. VA vs. VPl vs. LP Shunt
| Shunt Type | Route | Indication | Key Considerations |
|---|
| VP (ventriculoperitoneal) | Ventricle → peritoneum | First-line for most hydrocephalus | Most common; well-established; abdominal complications (pseudocyst, adhesions) |
| VA (ventriculoatrial) | Ventricle → right atrium via jugular vein | Peritoneal adhesions, peritoneal infection/malignancy | Risk of shunt nephritis (immune complex GN), endocarditis, pulmonary embolism, pulmonary HTN |
| VPl (ventriculopleural) | Ventricle → pleural space | When peritoneal and atrial access unavailable | Risk of pleural effusion, dyspnea; rarely used |
| LP (lumboperitoneal) | Lumbar thecal sac → peritoneum | Communicating hydrocephalus, IIH | CONTRAINDICATED in obstructive hydrocephalus (risk of tonsillar herniation); radiculopathy, acquired Chiari, high revision rate |
Warning
LP shunt in obstructive hydrocephalus — NEVER use a lumboperitoneal shunt when there is obstructive hydrocephalus. Draining CSF from the lumbar space without communication to the ventricles can precipitate downward tonsillar herniation and death.
Board Pearls
- Kocher’s point: 1 cm anterior to coronal suture, 2–3 cm lateral to midline — standard entry point for VP shunt and EVD placement
- Right lateral ventricle preferred for catheter placement (non-dominant hemisphere in most patients)
- Programmable valves are preferred for NPH — allow non-invasive pressure adjustment; some older models require reprogramming after MRI
- VA shunt complication: shunt nephritis (immune complex glomerulonephritis) — unique to VA shunts
- LP shunt contraindication: NEVER use in obstructive hydrocephalus — risk of downward herniation
Shunt Complications
Overview Table
| Complication | Incidence | Presentation | Management |
|---|
| Obstruction | Most common overall | Headache, nausea, vomiting, altered sensorium — recurrent hydrocephalus symptoms | Shunt revision; shunt tap to localize (proximal vs. distal) |
| Infection | 5–10% | Fever, wound erythema, shunt malfunction, abdominal pain (VP), bacteremia (VA); usually <6 months | Complete shunt removal + EVD + IV antibiotics × 10–14 days → re-shunt |
| Over-drainage | Variable | Subdural hematomas/hygromas, slit ventricle syndrome, positional headaches (worse upright) | Programmable valve adjustment (increase pressure), anti-siphon device |
| Disconnection/fracture | Uncommon | Shunt failure; palpable gap in tubing; visible on shunt series X-ray | Surgical reconnection or replacement |
| Migration | Rare | Catheter tip into brain parenchyma, bowel, scrotum | Surgical repositioning |
| Abdominal pseudocyst | Rare | Loculated CSF collection at distal tip; may be infected or sterile; abdominal mass/pain | Drainage + distal catheter revision; rule out infection |
| Bowel perforation | Very rare | Peritonitis, catheter protruding from rectum (rare case reports) | Emergent surgery; externalize shunt; antibiotics |
Shunt Infection
- Most common organism: Staphylococcus epidermidis (coagulase-negative staph) — skin flora introduced at surgery
- Timing: most infections present within 6 months (usually 1–2 months post-op)
- Late infections: consider hematogenous seeding; Staph aureus, gram-negative organisms
- Treatment requires hardware removal — antibiotics alone are insufficient; complete shunt removal + EVD + targeted IV antibiotics → CSF sterilization confirmed → new shunt
- Antibiotic-impregnated catheters: rifampin + clindamycin; reduce infection rate
Obstruction
- Most common long-term shunt complication
- Proximal obstruction > distal — choroid plexus, brain tissue, or debris blocks ventricular catheter
- Distal obstruction: omentum, adhesions, or pseudocyst blocks peritoneal end
- 50% of pediatric VP shunts fail within 2 years
Over-Drainage Syndromes
- Subdural hygromas/hematomas: excessive CSF drainage → brain sag → bridging vein stretch → subdural collections; especially in elderly NPH patients
- Slit ventricle syndrome: chronic over-drainage → very small ventricles + intermittent high-pressure headaches; decreased ventricular compliance → small volume changes cause large ICP spikes
- Low-pressure headaches: positional (worse upright, better supine); may see pachymeningeal enhancement on MRI
- Management: increase valve pressure setting (programmable valves), add anti-siphon device, horizontal valve systems; subtemporal craniectomy for refractory slit ventricle syndrome
Evaluating Shunt Malfunction
- Shunt series: plain X-rays of skull, neck, chest, abdomen — assess catheter continuity, kinks, disconnections, migration
- CT head: compare ventricle size to baseline; interval enlargement suggests obstruction/failure
- Shunt tap: access reservoir with butterfly needle; measure opening pressure; aspirate CSF for culture; inability to aspirate → proximal obstruction; slow refill → distal obstruction
- Nuclear shunt study (shuntogram): radionuclide injected into reservoir; tracks CSF flow through system; identifies obstruction site
Clinical Pearl
A patient with a VP shunt presenting with headache, nausea, and lethargy should be assumed to have shunt malfunction until proven otherwise. Order a shunt series + CT head immediately. Do not reassure based on small ventricles alone — slit ventricle syndrome can present with normal or small ventricles despite elevated ICP.
Board Pearls
- Staph epidermidis is the #1 shunt infection organism — NOT Staph aureus; presents within 6 months
- Shunt infection treatment = remove the hardware — antibiotics alone are insufficient; place EVD, treat, then re-shunt
- Obstruction is the most common long-term shunt complication; proximal (ventricular catheter) > distal
- Over-drainage → subdural hematoma: bridging veins stretch as brain sags away from skull; especially in elderly NPH patients
- Shunt series = skull + chest + abdomen X-rays — first step to evaluate shunt continuity and catheter position
- Shunt tap: cannot aspirate = proximal obstruction; slow refill = distal obstruction
ETV (Endoscopic Third Ventriculostomy)
Mechanism & Technique
- Mechanism: endoscopic fenestration of the floor of the 3rd ventricle → creates CSF pathway from 3rd ventricle to prepontine cistern → bypasses aqueductal obstruction
- Approach: endoscope inserted via right frontal burr hole into lateral ventricle → through foramen of Monro → visualize floor of 3rd ventricle → perforate between infundibular recess and mammillary bodies
- Critical anatomy: basilar artery lies directly beneath the floor of the 3rd ventricle — the most feared complication is basilar artery injury
Indications & Contraindications
- Best indication: obstructive hydrocephalus — especially aqueductal stenosis, tectal glioma, posterior fossa tumors compressing the aqueduct
- Contraindicated: communicating hydrocephalus (no obstruction to bypass; fenestration will not improve CSF dynamics)
- Success rate: 70–90% for aqueductal stenosis in adults; lower in infants <6 months (immature CSF absorption pathways)
- Advantage over VP shunt: no implanted hardware; no shunt dependence; lower long-term complication rate
ETV Success Score (ETVSS)
- Components: age + etiology + prior shunt — each scored; total 0–90
- Favorable factors: age >2 years, aqueductal stenosis/tectal tumor etiology, no prior shunt
- Unfavorable factors: age <1 month, post-hemorrhagic/post-infectious etiology, prior shunt failure
- ETVSS ≥70: ETV likely to succeed
- ETVSS <40: VP shunt preferred
Complications
- Basilar artery injury: most feared — can be fatal; basilar artery lies immediately beneath the 3rd ventricle floor
- CSF leak
- Infection/ventriculitis
- Delayed failure: stoma closure weeks to months later; presents as recurrent hydrocephalus; may need repeat ETV or VP shunt
- Hypothalamic injury: rare; from manipulation near hypothalamic structures
ETV + Choroid Plexus Cauterization (ETV-CPC)
- Combines ETV with bilateral choroid plexus cauterization → reduces CSF production + bypasses obstruction
- Indication: infantile hydrocephalus, particularly in resource-limited settings where shunt follow-up is difficult
- Most studied in sub-Saharan Africa: alternative to VP shunt in infants with post-infectious hydrocephalus
- Best outcomes: children >1 year with aqueductal stenosis
VP Shunt vs. ETV Comparison
| Feature | VP Shunt | ETV |
|---|
| Mechanism | External drainage to peritoneum | Internal bypass (3rd ventricle floor fenestration) |
| Best for | Communicating hydrocephalus, NPH, failed ETV | Obstructive hydrocephalus (aqueductal stenosis, posterior fossa tumor) |
| Hardware | Yes (catheter + valve) | No implanted hardware |
| Infection risk | 5–10% | <5% |
| Long-term revision | High (50% pediatric failure at 2 years) | Low if initially successful |
| Unique risk | Distal obstruction, migration, over-drainage | Basilar artery injury, late stoma closure |
Board Pearls
- ETV is treatment of choice for aqueductal stenosis — no hardware implanted; VP shunt reserved for failures or communicating hydrocephalus
- ETV Success Score: age + etiology + prior shunt — ETVSS ≥70 favors ETV; <40 favors VP shunt
- Basilar artery injury is the most feared ETV complication — artery lies directly beneath the 3rd ventricle floor
- ETV-CPC: combines fenestration + choroid plexus cauterization; alternative to shunt in infantile hydrocephalus
- ETV failure rate is higher in infants <6 months — immature CSF absorption pathways
Normal Pressure Hydrocephalus (NPH)
Clinical Presentation — Hakim Triad
- “Wet, Wacky, Wobbly” — the classic mnemonic for the Hakim triad
- Gait apraxia (wobbly): FIRST symptom to appear and MOST responsive to shunting; magnetic gait (feet appear “stuck to the floor”), wide-based, short-stepped, en bloc turns; resembles lower-body parkinsonism
- Dementia (wacky): subcortical pattern — psychomotor slowing, impaired attention, executive dysfunction; memory relatively preserved early (unlike AD); LEAST reliably improved by shunting
- Urinary incontinence (wet): initially urgency/frequency, later frank incontinence; intermediate shunt response
- Order of appearance: gait → dementia → incontinence; all three present in only ~50–60% at diagnosis
- Key distinction from AD: NPH gait is abnormal early; AD patients walk normally until late stages
- Key distinction from Parkinson disease: NPH lacks tremor and rigidity; both have shuffling gait, but NPH has wider base
- Key distinction from vascular dementia: vascular dementia has stepwise decline, focal deficits, and lacunar infarcts on imaging
Pathophysiology
- Impaired CSF absorption at arachnoid granulations → intermittent pressure elevations (B-waves) despite “normal” single-measurement opening pressure
- iNPH (idiopathic): most common form; typically age >60; no identifiable cause
- Secondary NPH: post-SAH, post-meningitis, post-TBI — better shunt response than iNPH (known etiology)
Imaging
| Finding | Description | Significance |
|---|
| Evans index >0.3 | Maximum frontal horn width ÷ maximum inner skull diameter | Screening tool for ventriculomegaly; not specific for NPH; must be out of proportion to sulcal atrophy |
| DESH sign | Disproportionately Enlarged Subarachnoid-space Hydrocephalus — tight high-convexity sulci with dilated Sylvian fissures | Suggests impaired CSF absorption at vertex; supports iNPH diagnosis |
| Callosal angle <90° | Measured on coronal MRI at posterior commissure level | Normal >100°; acute angle supports NPH |
| Periventricular edema | T2/FLAIR hyperintensity around ventricles (transependymal flow) | Suggests active hydrocephalus with CSF seeping through ependyma |
| Aqueductal flow void | Prominent CSF flow void through aqueduct on T2 MRI | Indicates hyperdynamic CSF flow; supports NPH |
Shunt Responsiveness Testing
| Test | Method | Interpretation |
|---|
| Large-volume LP (tap test) | Remove 30–50 mL CSF; assess gait before and at 1–4 hours and 24 hours post-tap | Gait improvement = positive predictor of shunt response; specificity ~90% but sensitivity only ~50–60% |
| Extended lumbar drainage (ELD) | External lumbar drain for 72 hours; drain ~150–300 mL CSF | More sensitive than single tap test (~80–90%); better predictor of shunt response; use when tap test equivocal |
| CSF infusion study (Rout) | Measure CSF outflow resistance via lumbar or ventricular infusion | Elevated Rout >12–18 mmHg/mL/min predicts shunt response |
| Opening pressure | Measured at LP | Normal or high-normal (<18 cmH2O) — “normal pressure”; intermittent B-waves on continuous monitoring |
Clinical Pearl
Negative tap test does NOT rule out NPH — sensitivity is only ~50–60%. If clinical suspicion remains high, proceed to extended lumbar drainage (ELD), which has ~80–90% sensitivity. Video gait assessment before and after LP is the most practical bedside documentation tool.
Shunt Response & Outcomes
- Overall: 60–80% of properly selected NPH patients improve after shunting
- Gait: best response — >80% improve; often within days to weeks
- Incontinence: intermediate response — ~50–70% improve
- Cognition: least reliable response — ~30–50% improve; longer symptom duration = worse cognitive recovery
- Programmable valves preferred for NPH — allow non-invasive pressure adjustment
- Predictors of good shunt response: positive tap test, short symptom duration (<2 years), gait-predominant presentation, known secondary cause, DESH pattern on MRI
NPH Differential Diagnosis
| Condition | Key Distinguishing Feature |
|---|
| Alzheimer disease | Cortical (amnestic) dementia pattern; normal gait until late; hippocampal atrophy; sulcal atrophy proportionate to ventricular size |
| Vascular dementia | Stepwise decline; focal deficits; white matter disease and lacunar infarcts on MRI |
| Parkinson disease | Rest tremor, rigidity, bradykinesia; asymmetric onset; DaTscan abnormal; responds to levodopa |
| Ex vacuo ventriculomegaly | Sulcal enlargement proportionate to ventricular dilation; no periventricular edema; no gait apraxia |
Board Pearls
- “Wet, wacky, wobbly” = incontinence, dementia, gait apraxia — gait is FIRST and MOST responsive to shunting
- Evans index >0.3 = ventriculomegaly; must be out of proportion to sulcal atrophy to suggest NPH
- Large-volume LP (30–50 mL) with gait improvement → predicts shunt success (high specificity ~90%, moderate sensitivity ~50–60%)
- Extended lumbar drainage is MORE sensitive than single tap test — use when tap test is equivocal and suspicion remains
- NPH vs. AD: NPH gait is abnormal early + subcortical dementia; AD has normal gait until late + cortical (amnestic) pattern
- Gait most responsive, dementia least responsive to shunting — the longer the symptoms, the worse the cognitive recovery
- Secondary NPH (post-SAH, post-meningitis) responds better to shunting than idiopathic NPH
Pseudotumor Cerebri (IIH) — Surgical Management
Overview
- Idiopathic intracranial hypertension (IIH): elevated ICP without hydrocephalus, mass lesion, or venous sinus thrombosis
- Classic patient: obese woman of childbearing age with headache, papilledema, visual obscurations, pulsatile tinnitus
- Diagnosis: modified Dandy criteria — elevated opening pressure (>25 cmH2O in adults), normal CSF composition, normal neuroimaging (may show empty sella, optic nerve sheath distension, posterior globe flattening, transverse sinus stenosis)
Medical Management (First-Line)
- IIHTT trial: acetazolamide (up to 4 g/day) + weight loss → improved visual fields, reduced papilledema, and lowered CSF pressure compared to placebo + weight loss
- Weight loss: 5–10% body weight reduction can significantly improve symptoms; bariatric surgery for morbid obesity
- Acetazolamide: carbonic anhydrase inhibitor; reduces CSF production; side effects include paresthesias, dysgeusia, metabolic acidosis, nephrolithiasis
- Topiramate: alternative — weak carbonic anhydrase inhibitor + appetite suppression (weight loss benefit)
- Serial LP: temporary measure only; not definitive treatment
Surgical Indications
- Progressive vision loss despite maximal medical therapy (acetazolamide + weight loss)
- Fulminant IIH with rapid visual decline (surgical emergency — do not wait for medical therapy to fail)
- Intractable headache refractory to medical therapy
Surgical Options
| Procedure | Mechanism | Best For | Key Points |
|---|
| Optic nerve sheath fenestration (ONSF) | Slits in optic nerve sheath → CSF drains from peri-optic subarachnoid space | Vision loss (primary indication) | Protects optic nerve; less effective for headache; can be unilateral (often improves contralateral eye); may need repeat |
| LP shunt | Lumbar thecal sac → peritoneum | Headache-predominant or bilateral visual loss | Traditional first-line CSF diversion for IIH; high revision rate (50–80%); risks include over-drainage, acquired Chiari, radiculopathy |
| VP shunt | Ventricle → peritoneum | If ventricles large enough to catheterize | Technically difficult in IIH (small ventricles); image-guided placement may be needed; lower revision rate than LP shunt |
| Venous sinus stenting | Stent across transverse sinus stenosis → reduces venous pressure → improves CSF absorption | Documented transverse sinus stenosis with gradient >8 mmHg | ~80% headache improvement; requires catheter venography with manometry; in-stent thrombosis risk; lifelong antiplatelet therapy; growing evidence base |
Choosing the Right Procedure
- Vision loss predominant → ONSF
- Headache predominant → CSF diversion (LP or VP shunt)
- Documented venous sinus stenosis with gradient >8 mmHg → venous sinus stenting
- Fulminant IIH (rapid visual decline) → emergent ONSF or shunt; do not delay
LP Shunt vs. VP Shunt in IIH
| Feature | LP Shunt | VP Shunt |
|---|
| Traditional role | First-line CSF diversion for IIH | Second-line (ventricles often too small) |
| Revision rate | Higher (50–80% need revision) | Lower revision rate |
| Technical challenge | Easier (no ventricular access needed) | Difficult with slit-like ventricles; may need image guidance |
| Unique complications | Acquired Chiari, radiculopathy, tonsillar herniation | Standard VP shunt complications |
Clinical Pearl
Fulminant IIH (rapid visual decline over days) is a surgical emergency. Perform emergent ONSF or shunt placement immediately — do not wait for a trial of medical therapy. Loss of vision in IIH can be permanent if intervention is delayed.
Board Pearls
- IIHTT trial: acetazolamide + weight loss is first-line; surgery reserved for refractory or fulminant cases
- ONSF protects vision but does NOT reliably treat headache — key distinction for choosing surgical approach
- LP shunt in IIH: traditional first-line CSF diversion but has high revision rate (50–80%); can cause acquired Chiari malformation
- Venous sinus stenting: emerging option for documented stenosis with trans-stenotic gradient >8 mmHg on catheter venography
- Vision loss predominant → ONSF; headache predominant → shunt — match procedure to predominant symptom
Pediatric Hydrocephalus
Etiology
| Cause | Mechanism | Key Features |
|---|
| Myelomeningocele | Open neural tube defect → Chiari II malformation → obstructive hydrocephalus | 80–90% develop hydrocephalus requiring VP shunt; virtually always associated with Chiari II (cerebellar vermis + brainstem + 4th ventricle herniate through foramen magnum) |
| IVH of prematurity | Germinal matrix hemorrhage → blood products obstruct CSF flow/absorption | Grade III (IVH with ventricular dilation) and Grade IV (periventricular hemorrhagic infarction) → highest risk; temporize with ventricular reservoir (Ommaya) or subgaleal shunt before permanent VP shunt |
| Congenital aqueductal stenosis | Narrowing of aqueduct of Sylvius — most common cause of congenital hydrocephalus | X-linked (L1CAM mutation): adducted thumbs, intellectual disability, corpus callosum hypoplasia; or sporadic; lateral + 3rd ventricles dilated, 4th ventricle normal |
| Dandy-Walker malformation | Cystic dilation of 4th ventricle + cerebellar vermis hypoplasia/absence + enlarged posterior fossa | Hydrocephalus in ~80%; associated with corpus callosum agenesis, cardiac defects; NOT the same as mega cisterna magna (which has normal vermis) |
| Posterior fossa tumors | Mass effect compresses 4th ventricle or aqueduct | Medulloblastoma, pilocytic astrocytoma, ependymoma; acute headache, vomiting, ataxia, papilledema |
| Congenital infections (TORCH) | Ependymitis → aqueductal obstruction or meningeal scarring | CMV: periventricular calcifications; toxoplasmosis: diffuse intracranial calcifications |
Clinical Signs in Infants
- Macrocephaly: head circumference crossing percentiles; most sensitive early sign
- Bulging anterior fontanelle: tense and full (normally flat/soft)
- Split sutures: widened cranial sutures (not yet fused in infants)
- Sun-setting eyes: forced downward gaze with sclera visible above iris; due to pressure on tectal plate/superior colliculi
- Scalp vein distension: prominent superficial veins from elevated ICP
- Irritability, poor feeding, vomiting: nonspecific signs of elevated ICP
- Macewen sign (“cracked pot”): resonant percussion sound over skull due to split sutures
Management of IVH-Related Hydrocephalus
- Temporizing measures (premature neonates too small/unstable for permanent shunt):
- Ventricular reservoir (Ommaya): subcutaneous reservoir connected to ventricular catheter; allows serial tapping to drain CSF
- Subgaleal shunt: ventricular catheter drains CSF into subgaleal pocket; temporizing before permanent VP shunt
- Serial ventricular taps / lumbar punctures: bridge measures
- Permanent VP shunt: placed when infant reaches ~2 kg and is medically stable; high revision rate in neonates
Chiari Malformations
| Type | Pathology | Associations | Surgery |
|---|
| Chiari I | Cerebellar tonsils herniate >5 mm below foramen magnum | Syringomyelia (50–70%); small posterior fossa; NOT associated with myelomeningocele | Symptomatic or syringomyelia → suboccipital decompression ± duraplasty |
| Chiari II | Vermis, brainstem, 4th ventricle herniate through foramen magnum | Myelomeningocele (~100%); hydrocephalus (~90%) | VP shunt for hydrocephalus; posterior fossa decompression for brainstem compression |
| Chiari III | Chiari II + occipital or high cervical encephalocele | Very rare; severe; poor prognosis | Encephalocele repair; shunt as needed |
L1CAM Mutation — X-Linked Aqueductal Stenosis
- X-linked recessive — affects males
- Clinical features: hydrocephalus + adducted (clasped) thumbs + intellectual disability + corpus callosum hypoplasia
- L1CAM gene: encodes L1 cell adhesion molecule; important for neural development
- Also known as HSAS (hydrocephalus with stenosis of the aqueduct of Sylvius)
Warning
IVH of prematurity — do not place permanent VP shunt in acute phase. CSF protein and blood products will obstruct the shunt. Temporize with ventricular reservoir or subgaleal shunt until CSF clears and infant is ≥2 kg.
Board Pearls
- Myelomeningocele: 80–90% develop hydrocephalus; virtually always associated with Chiari II malformation
- Aqueductal stenosis = most common cause of congenital hydrocephalus; X-linked form (L1CAM) — look for adducted thumbs + intellectual disability
- Sun-setting eyes = pressure on tectal plate → forced downward gaze; classic sign of hydrocephalus in infants
- Chiari II = myelomeningocele — virtually always associated; Chiari I is NOT
- Dandy-Walker: cystic 4th ventricle + absent/hypoplastic vermis + enlarged posterior fossa — NOT the same as mega cisterna magna (which has normal vermis)
- IVH Grade III–IV: temporize with ventricular reservoir or subgaleal shunt; permanent VP shunt when stable and ≥2 kg
- Chiari I + syringomyelia: cape-like dissociated sensory loss (pain/temp lost, light touch preserved) — classic board presentation
Special Considerations & Board-Relevant Scenarios
Acute Hydrocephalus — Emergency Management
- External ventricular drain (EVD): emergent CSF diversion; catheter in lateral ventricle connected to external collection system; allows both ICP monitoring and CSF drainage
- Indications: acute obstructive hydrocephalus, shunt malfunction with acute deterioration, IVH, infected shunt (temporizing during treatment)
- Kocher’s point: 1 cm anterior to coronal suture, 2–3 cm lateral to midline (mid-pupillary line); aim toward medial canthus (coronal) and tragus (sagittal)
- EVD complications: ventriculitis (~10%; Staph epidermidis most common), catheter malposition, over-drainage, hemorrhage along tract
Post-SAH Hydrocephalus
- Acute hydrocephalus: ~20–30% of SAH patients; blood in ventricles/subarachnoid space blocks CSF flow; requires emergent EVD
- Chronic hydrocephalus: ~10–20% require permanent VP shunt; communicating type from impaired arachnoid granulation absorption
- Risk factors for shunt dependence: higher Fisher grade, poor Hunt-Hess grade, IVH, older age, posterior circulation aneurysm
Slit Ventricle Syndrome
- Definition: chronically over-drained ventricles (slit-like on imaging) with episodic symptoms of raised ICP
- Pathophysiology: decreased ventricular compliance → small volume increases cause large pressure spikes; valve obstruction from collapsed ventricles around catheter
- Symptoms: intermittent severe headaches, nausea, lethargy
- Management: valve upgrade (higher pressure or programmable), anti-siphon device, cranial expansion (subtemporal craniectomy in refractory cases), ETV conversion
Shunts and MRI
- All modern VP shunts are MRI-conditional
- Programmable valves: older models may reset during MRI — always verify and reprogram valve settings after scanning
- Newer MRI-resistant programmable valves (e.g., Codman Certas Plus, Medtronic Strata) maintain settings through 3T MRI
Shunt in Pregnancy
- VP shunt generally functions well during pregnancy
- Vaginal delivery is generally safe with functioning VP shunt
- Monitor for shunt malfunction in third trimester (increased intra-abdominal pressure may impair distal flow)
- Distal catheter may need repositioning if peritoneal adhesions develop
Clinical Pearl
Posterior fossa hemorrhage/mass with acute hydrocephalus — EVD placement may be life-saving but can precipitate upward herniation if CSF is drained rapidly without addressing the posterior fossa pathology. Always coordinate with neurosurgery before EVD placement in posterior fossa emergencies.
Board Pearls
- Kocher’s point: 1 cm anterior to coronal suture, 2–3 cm lateral to midline — standard EVD/VP shunt entry point
- Post-SAH hydrocephalus: acute (EVD) in ~20–30%; chronic VP shunt needed in ~10–20%
- Slit ventricle syndrome: over-drained + intermittent high ICP episodes; do NOT assume the shunt is working just because ventricles are small
- EVD ventriculitis rate ~10%: Staph epidermidis most common; prophylactic antibiotics and antibiotic-impregnated catheters reduce risk
- Programmable valve + MRI: always check and reprogram valve settings after MRI in patients with older programmable valves
